[Federal Register: June 29, 2010 (Volume 75, Number 124)]
[Proposed Rules]
[Page 37311-37339]
[DOCID:fr29jn10-20]

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Proposed Rules
                                                Federal Register
________________________________________________________________________

This section of the FEDERAL REGISTER contains notices to the public of
the proposed issuance of rules and regulations. The purpose of these
notices is to give interested persons an opportunity to participate in
the rule making prior to the adoption of the final rules.

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 25 and 33

[Docket No. FAA-2010-0636; Notice No. 10-10]
RIN 2120-AJ34

Airplane and Engine Certification Requirements in Supercooled
Large Drop, Mixed Phase, and Ice Crystal Icing Conditions

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of Proposed Rulemaking (NPRM).

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SUMMARY: The Federal Aviation Administration proposes to amend the
airworthiness standards applicable to certain transport category
airplanes certified for flight in icing conditions and the icing
airworthiness standards applicable to certain aircraft engines. The
proposed regulations would improve safety by addressing supercooled
large drop icing conditions for transport category airplanes most
affected by these icing conditions, mixed phase and ice crystal
conditions for all transport category airplanes, and supercooled large
drop, mixed phase, and ice crystal icing conditions for all turbine
engines. These proposed regulations are the result of information
gathered from a review of icing accidents and incidents.

DATES: Send your comments on or before August 30, 2010.

ADDRESSES: You may send comments identified by Docket Number FAA-2010-
0636 using any of the following methods:
     Federal eRulemaking Portal: Go to http://
www.regulations.gov and follow the online instructions for sending your
comments electronically.
     Mail: Send comments to Docket Operations, M-30; U.S.
Department of Transportation, 1200 New Jersey Avenue, SE., Room W12-
140, West Building Ground Floor, Washington, DC 20590-0001.
     Hand Delivery or Courier: Bring comments to Docket
Operations in Room W12-140 of the West Building Ground Floor at 1200
New Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal holidays.
     Fax: Fax comments to Docket Operations at<PHONE_NUMBER>.
    For more information on the rulemaking process, see the
SUPPLEMENTARY INFORMATION section of this document.
    Privacy: The FAA will post all comments we receive, without change,
to http://www.regulations.gov, including any personal information you
provide. Using the search function of our docket Web site, anyone can
find and read the electronic form of all comments received into any of
our dockets, including the name of the individual sending the comment
(or signing the comment for an association, business, labor union,
etc.). You may review DOT's complete Privacy Act Statement in the
Federal Register published on April 11, 2000 (65 FR 19477-78) or you
may visit http://DocketsInfo.dot.gov.
    Docket: To read background documents or comments received, go to
http://www.regulations.gov at any time and follow the online
instructions for accessing the docket. Or, go to Docket Operations in
Room W12-140 of the West Building Ground Floor at 1200 New Jersey
Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through
Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: For part 25 technical questions
contact Robert Hettman, FAA, Propulsion/Mechanical Systems Branch, ANM-
112, Transport Airplane Directorate, Aircraft Certification Service,
1601 Lind Avenue, SW., Renton, WA 98057-3356; telephone<PHONE_NUMBER>;
facsimile<PHONE_NUMBER>, e-mail<EMAIL_ADDRESS>    For part 33 technical questions contact John Fisher, FAA,
Rulemaking and Policy Branch, ANE-111, Engine and Propeller Directorate
Standards Staff, Aircraft Certification Service, 12 New England
Executive Park, Burlington, MA 01803; telephone<PHONE_NUMBER>,
facsimile<PHONE_NUMBER>, e-mail<EMAIL_ADDRESS>    For part 25 legal questions contact Douglas Anderson, FAA, Office
of the Regional Counsel, ANM-7, Northwest Mountain Region, 1601 Lind
Avenue, SW., Renton, WA 98057-3356; telephone<PHONE_NUMBER>; facsimile
(425) 227-1007, e-mail<EMAIL_ADDRESS>    For part 33 legal questions contact Vince Bennett, FAA, Office of
the Regional Counsel, ANE-007, New England Region, 12 New England
Executive Park, Burlington, MA 01803; telephone<PHONE_NUMBER>;
facsimile<PHONE_NUMBER>, e-mail<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: Later in this preamble under the Additional
Information section, the FAA discusses how you can comment on this
proposal and how the agency will handle your comments. Included in this
discussion is related information about the docket, privacy, and the
handling of proprietary or confidential business information. The FAA
also discusses how you can get a copy of this proposal and related
rulemaking documents.

Authority for This Rulemaking

    The FAA's authority to issue rules on aviation safety is found in
Title 49 of the United States Code. Subtitle I, section 106 describes
the authority of the FAA Administrator. Subtitle VII, Aviation
Programs, describes in more detail the scope of the agency's authority.
    This rulemaking is proposed under the authority described in
subtitle VII, part A, subpart III, section 44701, ``General
requirements.'' Under that section, the FAA is charged with promoting
safe flight of civil aircraft in air commerce by prescribing minimum
standards required in the interest of safety for the design and
performance of aircraft; regulations and minimum standards in the
interest of safety for inspecting, servicing, and overhauling aircraft;
and regulations for other practices, methods, and procedures the
Administrator finds necessary for safety in air commerce. This
regulation is within the scope of that authority because it would
prescribe--
     New safety standards for the design and performance of
certain transport category airplanes and aircraft engines; and
     New safety requirements that are necessary for the design,
production, and operation of those airplanes, and for other practices,
methods, and

procedures relating to those airplanes and engines.

Summary of the Proposal

    The FAA proposes to revise certain regulations in Title 14, Code of
Federal Regulations (14 CFR) part 25 (Airworthiness Standards:
Transport Category Airplanes) and part 33 (Airworthiness Standards:
Aircraft Engines) related to the certification of transport category
airplanes and turbine aircraft engines in icing conditions. We also
propose to create new regulations: Sec.  25.1324--Angle of attack
systems; Sec.  25.1420 SLD icing conditions; part 25, appendix O (SLD
icing conditions); part 33, appendix C (this will be intentionally left
blank as a placeholder); and part 33, appendix D (Mixed phase and ice
crystal icing conditions). To improve the safety of transport category
airplanes operating in SLD, mixed phase, and ice crystal icing
conditions, the proposed regulations would:
     Expand the certification icing environment to include
freezing rain and freezing drizzle.
     Require airplanes most affected by SLD icing conditions to
meet certain safety standards in the expanded certification icing
environment, including additional airplane performance and handling
qualities requirements.
     Expand the engine and engine installation certification,
and some airplane component certification regulations (for example,
angle of attack and airspeed indicating systems), to include freezing
rain, freezing drizzle, ice crystal, and mixed phase icing conditions.
For certain cases, a subset of these icing conditions is proposed.
    The benefits and costs are summarized below. The estimated benefits
are $405.6 million ($99.5 million present value). The total estimated
costs are $71.0 million ($54.0 million present value). On an annualized
basis, for the time period 2012-2064, the benefits are $7.0 million,
and the costs are $3.8 million.

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                                              Nominal benefits                     PV benefits
----------------------------------------------------------------------------------------------------------------
                                                    Benefits
----------------------------------------------------------------------------------------------------------------
Smaller & Medium Airplanes.................       $249,580,915  $69,994,259
Larger Airplanes...........................        156,004,884  29,498,469
    Total Benefits.........................        405,585,799  99,492,728
¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
                                                                (7.0 million annually)
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                                                      Costs
----------------------------------------------------------------------------------------------------------------
                                                Nominal cost    PV cost
----------------------------------------------------------------------------------------------------------------
Engine Cert Cost...........................          7,936,000  6,931,610
Engine Capital Cost........................          6,000,000  5,240,632
                                            --------------------------------------------------------------------
    Total Engine...........................         13,936,000  12,172,242
================================================================================================================
Smaller Airplane Certification Cost........         24,999,039  21,835,129
New Larger Airplane Certification Cost.....          3,154,600  2,755,350
Derivative Larger Airplane Certification            10,438,800  9,117,652
 Cost.
Hardware Costs.............................         10,390,000  5,842,024
Fuel Burn All..............................          8,046,676  2,261,941
================================================================================================================
    Total Costs............................         70,965,115  53,984,338
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                                                                ($3.8 million annually)
----------------------------------------------------------------------------------------------------------------

Background

    In the 1990s, the FAA became aware that the types of icing
conditions considered during the certification of transport category
airplanes and turbine aircraft engines needed to be expanded to
increase the level of safety during flight in icing. The FAA determined
that the revised icing certification standards should include
supercooled large drops (SLD), mixed phase, and ice crystals.\1\
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    \1\ Appendix 1 of this preamble contains definitions of certain
terms used in this notice of proposed rulemaking (NPRM).
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    Safety concerns about the adequacy of the icing certification
standards were brought to the forefront of public and governmental
attention by a 1994 accident in Roselawn, Indiana, involving an Avions
de Transport Regional ATR 72 series airplane. The FAA, Aerospatiale,
the French Direction G[eacute]n[eacute]ral de l'Aviation Civile, Bureau
Enquete Accident, the National Aeronautics and Space Administration,
the National Transportation Safety Board (NTSB), and others conducted
an extensive investigation of this accident. These investigations led
to the conclusion that freezing drizzle conditions created a ridge of
ice on the wing's upper surface aft of the deicing boots and forward of
the ailerons. It was further concluded that this ridge of ice
contributed to an uncommanded roll of the airplane. Based on its
investigation, the NTSB recommended changes to the icing certification
requirements.
    The certification requirements for icing conditions are specified
in part 25, appendix C. The atmospheric condition (freezing drizzle)
that contributed to the Roselawn accident is currently outside the
icing envelope for certifying transport category airplanes. The term
``icing envelope'' is used within part 25, appendix C, and this NPRM to
refer to the environmental icing conditions within which the airplane
must be shown to be able to safely operate. The term ``transport
category airplanes'' is used throughout this rulemaking document to
include all airplanes type certificated to part 25 regulations.
    Another atmospheric icing condition that is currently outside the
icing envelope is freezing rain. The FAA has not required airplane
manufacturers to show that airplanes can operate safely in freezing
drizzle or freezing rain conditions. These conditions constitute an
icing environment known as supercooled large drops (SLDs).
    As a result of this accident and consistent with related NTSB

recommendations \2\ the FAA tasked the Aviation Rulemaking Advisory
Committee (ARAC),\3\ through its Ice Protection Harmonization Working
Group (IPHWG), to do the following:
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    \2\ NTSB recommendations A-96-54 and A-96-56; available in the
Docket and on the Internet at: http://www.ntsb.gov/Recs/letters/
1996/A96_48_69.pdf.
    \3\ Published in the Federal Register, December 8, 1997 (62 FR
64621).
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     Define an icing environment that includes SLDs.
     Consider the need to define a mixed phase icing
environment (supercooled liquid and ice crystals).
     Devise requirements to assess the ability of an airplane
to either safely operate without restrictions in SLD and mixed phase
conditions or safely operate until it can exit these conditions.
     Study the effects icing requirement changes could have on
Sec. Sec.  25.773, Pilot compartment view; 25.1323, Airspeed indicating
system; and 25.1325, Static pressure systems.
     Consider the need for a regulation on ice protection for
angle of attack probes.
    This proposed rule is based on the ARAC's recommendations to the
FAA. Terms used in this notice of proposed rulemaking (NPRM) are
defined in Appendix 1 of this preamble.

A. Existing Regulations for Flight in Icing Conditions

    Currently, the certification regulations applicable to transport
category airplanes for flight in icing conditions require that: ``The
airplane must be able to operate safely in the continuous maximum and
intermittent maximum icing conditions of appendix C.'' \4\ The
certification regulations also require minimum performance and handling
qualities in these icing conditions and methods to detect airframe
icing and to activate and operate ice protection systems.\5\ Icing
regulations applicable to engines are in Sec. Sec.  33.68 and 33.77.
Operating regulations in parts 91 (General Operating and Flight Rules)
and 135 (Operating Requirements: Commuter and On Demand Operations)
address limitations in icing conditions for airplanes operated under
these parts.\6\ Part 121 (Operating Requirements: Domestic, Flag and
Supplemental Operations) addresses operations in icing conditions that
might adversely affect safety and requires installing certain types of
ice protection equipment and wing illumination equipment.\7\
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    \4\ 14 CFR 25.1419, Ice Protection.
    \5\ For a complete discussion of the regulations see Amendment
25-121 (72 FR 44665, August 8, 2007), and Amendment 25-129 (74 FR
38328, August 3, 2009).
    \6\ 14 CFR 91.527, Operating in icing conditions; and Sec.
135.227, Icing conditions: Operating limitations.
    \7\ 14 CFR 121.629(a), Operation in icing conditions and Sec.
121.341, Equipment for operations in icing conditions.
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    Some of the part 25 and 33 regulations specify that the affected
equipment must be able to operate in some or all of the icing
conditions defined in part 25, appendix C. Other regulations within
these parts do not specify the icing conditions that must be considered
for airplane certification, but, historically, airplane certification
programs have only considered icing conditions that are defined in
appendix C.
    Appendix C addresses continuous maximum and intermittent maximum
icing conditions within stratiform and cumuliform clouds ranging from
sea level up to 30,000 feet. Appendix C defines icing cloud
characteristics in terms of mean effective drop diameters, liquid water
content, temperature, horizontal and vertical extent, and altitude.
Icing conditions that contain drops with mean effective diameters that
are larger than the cloud mean effective drop diameters defined in
appendix C are typically referred to as freezing drizzle or freezing
rain. Icing conditions containing freezing drizzle and freezing rain
are not currently considered when certifying an airplane's ice
protection systems. Because the larger diameter drops typically impinge
farther aft on the airfoil, exposure to these conditions can result in
ice accretions aft of the ice protection area, which can negatively
affect airplane performance and handling qualities.
    Likewise, mixed phase (supercooled liquid and ice crystals) and
100% ice crystal icing conditions are not currently considered when
certifying an airplane's ice protection systems. Exposing engines and
externally mounted probes to these conditions could result in hazardous
ice accumulations within the engine that may result in engine damage,
power loss, and loss of or misleading airspeed indications. The
certification regulations for transport category airplanes and engines
do not address the safe operation of airplanes in SLD, mixed phase, or
ice crystal icing conditions and the operating rules do not
specifically prohibit operations in these conditions.

B. National Transportation Safety Board Safety Recommendations

    The NTSB issued NTSB Safety Recommendation Numbers A-96-54 \8\ and
A-96-56 \9\ as a result of the Roselawn accident previously discussed.
This rulemaking activity partially addresses the NTSB recommendations
because there are separate rulemaking activities associated with
revisions to 14 CFR part 23 regulations for small airplanes and 14 CFR
part 121 operational regulations. The NTSB recommendations are as
follows:
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    \8\ NTSB recommendation A-96-54; available in the Docket and on
the Internet at: http://www.ntsb.gov/Recs/letters/1996/A96_48_
69.pdf.
    \9\ NTSB recommendation A-96-56; available in the Docket and on
the Internet at: http://www.ntsb.gov/Recs/letters/1996/A96_48_
69.pdf.
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1. A-96-54
    Revise the icing criteria published in 14 Code of Federal
Regulations (CFR), parts 23 and 25, in light of both recent research
into aircraft ice accretion under varying conditions of liquid water
content, drop size distribution, and temperature, and recent
developments in both the design and use of aircraft. Also, expand the
appendix C icing certification envelope to include freezing drizzle/
freezing rain and mixed water/ice crystal conditions, as necessary.
(Class II, Priority Action) (A-96-54) (Supersedes A-81-116 and--118)
2. A-96-56
    Revise the icing certification testing regulation to ensure that
airplanes are properly tested for all conditions in which they are
authorized to operate, or are otherwise shown to be capable of safe
flight into such conditions. If safe operations can not be demonstrated
by the manufacturer, operational limitations should be imposed to
prohibit flight in such conditions and flightcrews should be provided
with the means to positively determine when they are in icing
conditions that exceed the limits for aircraft certification. (Class
II, Priority Action) (A-96-56)

C. Related Rulemaking Activity

    The ARAC's Ice Protection Harmonization Working Group (IPHWG)
submitted additional part 121 icing rulemaking recommendations to the
FAA that may lead to future rulemaking, but do not directly impact this
NPRM. Those recommendations would improve airplane safety when
operating in icing conditions. The recommendations would:
     Address when ice protection systems must be activated.

     Require some airplanes to exit all icing conditions after
encountering large drop icing conditions conducive to ice accretions
aft of the airframe's protected area.

D. Advisory Material

    The proposed new AC and revisions to existing ACs would provide
guidance material for one acceptable means, but not the only means, of
demonstrating compliance with the proposed regulations contained in
this NPRM. The guidance provided in these documents is directed at
airplane manufacturers, modifiers, foreign regulatory authorities, and
FAA transport airplane type certification engineers, flight test
pilots, and their designees. The proposed ACs will be posted on the
``Aircraft Certification Draft Documents Open for Comment'' Web site,
http://www.faa.gov/aircraft/draft_docs, after this NPRM is published
in the Federal Register
    For advisory material related to this NPRM, the FAA is:
     Developing a new AC 25-xx, Compliance of Transport
Category Airplanes with Certification Requirements for Flight in Icing
Conditions.
     Revising AC 20-147, Turbojet, Turboprop, and Turbofan
Engine Induction System Icing and Ice Ingestion.
     Revising AC 25-25, Performance and Handling
Characteristics in the Icing Conditions Specified in Part 25, Appendix
C.
     Revising AC 25.629-1A, Aeroelastic Stability
Substantiation of Transport Category Airplanes.
     Revising AC 25.1329-1B, Approval of Flight Guidance
Systems.

General Discussion of the Proposal

    The FAA proposes to revise certain regulations in parts 25 and 33
related to the certification of transport category airplanes and
turbine aircraft engines in icing conditions.
    We also propose to create a new: Sec.  25.1324--Angle of attack
systems; Sec.  25.1420--Supercooled large drop icing conditions; part
25, appendix O (supercooled large drop icing conditions; part 33,
appendix C (intentionally left blank); and part 33, appendix D (Mixed
phase and ice crystal icing conditions). Part 33, appendix C, is
intentionally left blank and retained as a placeholder for non-icing
related regulations so that part 33, appendix C, would not be confused
with the icing conditions defined in part 25, appendix C.
    To improve the safety of transport category airplanes operating in
SLD, mixed phase, and ice crystal icing conditions, the proposed
regulations would:
     Expand the certification icing environment to include
freezing rain and freezing drizzle.
     Require airplanes most affected by SLD icing conditions
(transport category airplanes with a maximum takeoff weight less than
60,000 pounds or with reversible flight controls) to meet certain
safety standards in the expanded certification icing environment,
including additional airplane performance and handling qualities
requirements.
     Expand the engine and engine installation certification,
and some airplane component certification regulations (for example,
angle of attack and airspeed indicating systems) to include freezing
rain, freezing drizzle, ice crystal, and mixed phase icing conditions.
For certain cases, a subset of these icing conditions is proposed.

A. Safety Concern

    The ARAC's IPHWG reviewed icing events involving transport category
airplanes and found accidents and incidents that are believed to have
occurred in icing conditions that are not addressed by the current
regulations. The icing conditions resulted in flightcrews losing
control of their aircraft and, in some cases, engine power loss. The
review found hull losses and fatalities associated with SLD conditions,
but not for ice crystal and mixed phase conditions. However, there have
been 14 documented cases of ice crystal and mixed phase engine power
loss events between 1988 through 2009. Of those events, there were 13
occurrences of multi-engine power loss events. Fifty percent of those
events were defined as ``aircraft level events,'' since they occurred
on multiple engines installed on the same airplane. Two of these
aircraft level events resulted in diversions.
    The incident history also indicates that flightcrews have
experienced temporary loss of or misleading airspeed indications in
icing. Airspeed indications on transport category airplanes are derived
from the difference between two air pressures--the total pressure, as
measured by a pitot tube mounted somewhere on the fuselage, and the
ambient or static pressure, as measured by a static port. The static
port may be flush mounted on the airplane fuselage or co-located on the
pitot tube. When the static and pitot systems are co-located, the
configuration is referred to as a pitot-static tube. Static ports are
not prone to collecting ice crystals, either because of their flush
mounted locations or their overall shape.
    Due to the way pitot or pitot-static tubes are usually mounted,
they are prone to collecting ice crystals. Encountering high
concentrations of ice crystals may lead to blocked pitot or pitot-
static tubes because the energy necessary to melt the ice crystals can
exceed the tubes' design requirements. Pitot or pitot-static tube
blockage can lead to errors in measuring airspeed. The regulatory
changes which add ice crystal conditions for airspeed indicating
systems are intended to apply to either a pitot tube or pitot-static
tube configuration.
    The IPHWG did not identify any events due to ice accumulations on
probes that are used to measure angle of attack, or other angle of
attack sensors. However, the IPHWG determined there are angle of attack
probe designs that are susceptible to mixed phase conditions.
    The IPHWG concluded that the current regulations do not adequately
address SLD, mixed phase, and ice crystal conditions. The concerns
regarding mixed phase and ice crystal conditions were limited to
engines, propulsion installations, airspeed indications, and angle of
attack systems. The FAA concurs with the IPHWG's conclusions.

B. Prior FAA Actions To Address the Safety Concern

    The FAA has issued airworthiness directives (ADs) to address the
unsafe conditions associated with operating certain airplanes in severe
icing conditions, which can include SLD icing conditions. These ADs are
applicable to airplanes equipped with both reversible flight controls
in the roll axis and pneumatic deicing boots. The ADs require the
flightcrews to exit icing when visual cues are observed that indicate
the conditions exceed the capabilities of the ice protection equipment.
In addition, for new certifications of airplanes equipped with
unpowered roll axis controls and pneumatic deicing boots, the airplanes
are evaluated to ensure the roll control forces are acceptable if the
airplane operates in certain SLD conditions. However, the scope of
these actions is limited because they do not address all transport
category airplanes and do not address the underlying safety concern of
the unknown performance and handling qualities safety margins for
airplanes and engines operating in freezing drizzle, freezing rain,
mixed phase, and ice crystal conditions. The IPHWG concluded there is a
need to improve the regulations to ensure safe operation

of airplanes and engines in these conditions.

C. Alternatives to Rulemaking

    Before proposing new rulemaking, the FAA considers alternative ways
to solve the safety issue under consideration. Following is a brief
discussion of two of the alternatives we considered during
deliberations on this proposed rule.
1. Alternative 1: Terminal Area Radar and Sensors
    The IPHWG considered the use of terminal area radar and ground-
based sensors to identify areas of SLDs so they can be avoided, rather
than require certification for operations in SLD. Equipment for
detecting and characterizing icing conditions in holding areas is being
developed. However, the equipment would have limited coverage area. For
areas not covered by terminal area radar and ground-based sensors,
airborne radars and sensors are being developed that would identify SLD
conditions in sufficient time for avoidance. These ground-based and
airborne systems are not mature enough to provide sufficient protection
for all flight operations affected by SLD. Even if the equipment was
mature, rulemaking would still be necessary to establish safety margins
for inadvertent flight into such conditions and to provide an option
for applicants to substantiate that the airplane is capable of safe
operation in SLD conditions.
2. Alternative 2: Icing Diagnostic and Predictive Weather Tools
    The IPHWG considered the use of icing diagnostic and predictive
weather tools to avoid SLD rather than certify an airplane to operate
in SLD conditions. Tools have been developed that can provide
information on icing and SLD potential, but may not report all
occurrences of SLD. These experimental tools are available on the
Internet and can be used to provide flight planning information
guidance for avoidance of SLD conditions. However, rulemaking would
still be necessary to establish safety margins for inadvertent flight
into such conditions and to provide an option for applicants to
substantiate that the airplane is capable of safe operation in SLD
conditions.

Discussion of the Proposed Regulatory Requirements

Appendix O to Part 25

    The proposed appendix O is structured like part 25, appendix C, one
part defining icing conditions and one defining ice accretions.
Appendix O, part I, would define SLD icing conditions and part II would
define the ice accretions that a manufacturer must consider when
designing an airplane.

Supercooled Large Drop Icing Conditions

    Proposed Sec.  25.1420 would add safety requirements that must be
met in SLD icing conditions for certain transport category airplanes to
be certified for flight in icing conditions. This change would require
evaluating the operation of these airplanes in the SLD icing
environment; developing a means to differentiate between different SLD
icing conditions, if necessary; and developing procedures to exit all
icing conditions.
    The proposed regulation would require consideration of the SLD
icing conditions (freezing drizzle and freezing rain) defined in a
proposed new part 25, appendix O, part I, in addition to the existing
part 25, appendix C, icing conditions. Proposed appendix O would
include drop sizes larger than those considered by current icing
regulations. These larger drops impinge and freeze farther aft on
airplane surfaces than the drops defined in appendix C and may affect
the airplane's performance, handling qualities, flutter
characteristics, and engine and systems operations. The appendix O
icing conditions, if adopted, may affect the design of airplane ice
protection systems.
    The SLD icing conditions described in the proposed appendix O would
be those in which the airplane must be able to either safely exit
following the detection of any or specifically identified appendix O
icing conditions, or safely operate without restrictions. Specifically,
the proposed Sec.  25.1420 would allow three options:
     Detect appendix O conditions and then operate safely while
exiting all icing conditions (Sec.  25.1420(a)(1)).
     Safely operate in a selected portion of appendix O
conditions, detect when the airplane is operating in conditions that
exceed the selected portion, and then operate safely while exiting all
icing conditions (Sec.  25.1420(a)(2)).
     Operate safely in all of the appendix O conditions (Sec.
25.1420(a)(3)).
    As discussed below in the section titled ``Differences from the
ARAC Recommendations,'' the proposed Sec.  25.1420 would apply to
airplanes with either: (1) a takeoff maximum gross weight of less than
60,000 pounds, or (2) reversible flight controls.
    To establish that an airplane could operate safely in the proposed
appendix O conditions described above, proposed Sec.  25.1420(b) would
require both analysis and one test, or more as found necessary, to
establish that the ice protection for the various components of the
airplane is adequate. The words ``as found necessary'' would be applied
in the same way as they are applied in Sec.  25.1419(b). During the
certification process, the applicant would demonstrate compliance with
the rule using a combination of analyses and test(s). The applicant's
means of compliance would consist of analyses and the amount and types
of testing it finds necessary to demonstrate compliance with the
regulation. The applicant would choose to use one or more of the tests
identified in paragraphs Sec.  25.1420(b)(1) through (b)(5). Although
the applicant may choose the means of compliance, it is ultimately the
FAA that determines whether the applicant has performed sufficient
test(s) and analyses to substantiate compliance with the regulation.
Similarly, the words ``as necessary,'' which appear in Sec.
25.1420(b)(3) and (b)(5), would result in the applicant choosing the
means of compliance that is needed to support the analysis, but the FAA
would make a finding whether the means of compliance is acceptable. If
an applicant has adequate data a similarity analysis may be used in
lieu of the testing required by Sec.  25.1420(b). For an airplane
certified to operate in at least a portion of proposed appendix O icing
conditions, proposed Sec.  25.1420(c) would extend the requirements of
Sec.  25.1419(e), (f), (g), and (h) \10\ to include activation and
operation of airframe ice protection systems in the appendix O icing
conditions for which the airplane is certified. Proposed Sec.
25.1420(c) would not apply to airplanes certified to proposed Sec.
25.1420(a)(1) because proposed Sec.  25.1420(a)(1) would require a
method to identify and safely exit all appendix O conditions.
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    \10\ These requirements were recently adopted in Amendment 25-
129 (74 FR 38328, August 3, 2009). Generally, that amendment
requires methods to detect airframe icing and to activate and
operate ice protection systems.
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    The proposed appendix O defines SLD conditions. It was developed by
the ARAC IPHWG, which included meteorologists and icing research
specialists from industry, FAA/FAA Tech Center, Meteorological Services
of Canada, National Aeronautics and Space Administration (NASA), and
Transport Canada/Transport Development Center. The IPHWG collected and
analyzed airborne measurements of pertinent SLD variables, developed an
engineering standard to be used in aircraft certification, and
recommended that

standard to the FAA. The FAA concurs with the recommendation.
    The SLD conditions defined in appendix O, part I, include freezing
drizzle and freezing rain conditions. The freezing drizzle and freezing
rain environments are further divided into conditions in which the drop
median volume diameters are either less than or greater than the 40
microns. Appendix O consists of measured data that was divided into
drop distributions within these four icing conditions. These
distributions were averaged to produce the representative distributions
for each condition.
    The distributions of drop sizes are defined as part of appendix O.
The need to include the distributions comes from the larger amount of
mass in the larger drop diameters of appendix O. The water mass of the
larger drops affects the amount of water that impinges on airplane
components, the drop impingement, icing limits, and the ice buildup
shape.
    Appendix O provides a liquid water content scale factor that would
be used to adjust the liquid water content for freezing drizzle and
freezing rain. The scale factor is based on the liquid water contents
of continuous freezing drizzle and freezing rain conditions decreasing
with increasing horizontal extents.

Performance and Handling Qualities

    The ice accretion definitions in proposed appendix O, part II, and
the proposed revisions to the performance and handling qualities
requirements for flight in icing conditions are similar to those
required for flight in appendix C icing conditions. The proposals
address the three options allowed by proposed Sec.  25.1420(a).
Proposed appendix O, part II, would contain definitions of the ice
accretions appropriate to each phase of flight. The proposed appendix
O, part II(b), would define the ice accretions used to show compliance
with the performance and handling qualities requirements for any
portion of appendix O in which the airplane is not certified to
operate. The proposed appendix O, part II(c), would define the ice
accretions for any portion of appendix O in which the airplane is
certified to operate.
    Proposed appendix O, part II(d), would define the ice accretion in
appendix O conditions before the airframe ice protection system is
activated and is performing its intended function to reduce or
eliminate ice accretions on protected surfaces. This ice accretion
would be used in showing compliance with the controllability and stall
warning margin requirements of Sec. Sec.  25.143(j) and 25.207(h),
respectively, that apply before the airframe ice protection system has
been activated and is performing its intended function. Even if the
airplane is certified to operate only in a portion of the appendix O
icing conditions, the ice accretion used to show compliance with
Sec. Sec.  25.143(j) and 25.207(h) must consider all appendix O icing
conditions since the initial entry into icing conditions may be into
appendix O icing conditions in which the airplane is not certified to
operate.
    To reduce the number of ice accretions needed to show compliance
with Sec.  25.21(g), the proposed appendix O, part II(e), would allow
the option of using an ice accretion defined for one flight phase for
any other flight phase if it is shown to be more critical than the ice
accretion defined for that other flight phase.
    Existing Sec.  25.21(g)(1) \11\ requires that the performance and
handling qualities requirements of part 25, subpart B, with certain
exceptions,\12\ be met in appendix C icing conditions.\13\ Proposed
Sec.  25.21(g)(3) would identify the performance and handling qualities
requirements that must be met to ensure that an airplane certified to
either the proposed Sec.  25.1420(a)(1) or (a)(2) could safely exit
icing if the icing conditions of proposed appendix O, for which
certification is not sought, are encountered. Such an airplane would
not be approved to take off in proposed appendix O icing conditions and
would only need to be able to detect and safely exit those icing
conditions encountered en route. Therefore, it is proposed that, in
addition to the exceptions identified in the existing Sec.
25.21(g)(1), such an airplane would not need to meet certain
requirements \14\ for appendix O icing conditions.
---------------------------------------------------------------------------

    \11\ 14 CFR 25.21(g)(1) is proposed to be redesignated as Sec.
25.21(g)(2).
    \12\ The exceptions listed in this requirement are Sec. Sec.
25.121(a), 25.123(c), 25.143(b)(1) and (b)(2), 25.149, 25.201(c)(2),
25.207(c) and (d), 25.239, and 25.251(b) through (e).
    \13\ For a complete discussion of these requirements, see
Amendment 25-121 (72 FR 44665, August 8, 2007).
    \14\ 14 CFR 25.105, 25.107, 25.109, 25.111, 25.113, 25.121, and
25.123.
---------------------------------------------------------------------------

    With one exception, for an airplane certified under proposed Sec.
25.1420(a)(1) or (a)(2), the same handling qualities requirements that
must currently be met for flight in appendix C icing conditions are
proposed for flight in appendix O icing conditions for which
certification is not sought. That exception is Sec.  25.143(c)(1),
which addresses controllability following engine failure during takeoff
at V2. Compliance with that rule would not be necessary
since the airplane would not be approved for takeoff in appendix O
icing conditions. No justification for a relaxation of other handling
qualities requirements could be identified.
    The requirements for safe operation in all or any portion of
proposed appendix O icing conditions under proposed Sec.  25.21(g)(4)
are similar to those currently required for appendix C icing
conditions. With one exception, the list of part 25, subpart B
requirements that currently do not have to be met for flight in
appendix C icing conditions would not have to be met in proposed
appendix O icing conditions. The exception is that compliance with
Sec.  25.121(a), Climb: One-engine-inoperative would be required for
appendix O icing conditions because, unlike for appendix C icing
conditions, the FAA cannot justify an assumption that the ice accretion
in this flight phase can be assumed insignificant. In practice, it is
expected that some applicants may use an operating limitation to
prohibit takeoff in appendix O icing conditions. Otherwise, the same
rationales behind the requirements are used for both appendix C and
appendix O icing conditions. For continued operation in appendix O
icing conditions, there should effectively be no degradation in
handling qualities, and any degradation in performance should be no
greater than that allowed by the regulations for appendix C icing
conditions.

Component Requirements for All Part 25 Transport Category Airplanes

    In certification programs, both the airplane as a whole and its
individual components are evaluated for flight in icing conditions.
There are several rules in part 25 \15\ that contain icing related
requirements for specific components. We propose to revise those rules
to ensure the airplane can safely operate in the new icing conditions
established in this proposed rule.
---------------------------------------------------------------------------

    \15\ 14 CFR 25.773, 25.929, 25.1093, 25.1323, and 25.1325.
---------------------------------------------------------------------------

    Section 25.1419 requires that an airplane be able to safely operate
in all of the conditions specified in appendix C, whereas the proposed
Sec.  25.1420 would not require an airplane to safely operate in all of
the appendix O icing conditions. Proposed Sec.  25.1420(a)(1) and
(a)(2) only require an airplane to be capable of safely exiting icing
conditions after encountering an appendix O icing condition for which
that airplane will not be certified. The existing regulations for pilot
compartment view, airspeed indication

system, and static pressure system \16\ contain requirements for
operation in icing conditions. These sections would be revised to add
requirements for operation in appendix O icing conditions. Section
25.1323, Airspeed indicating system, would also be revised to include
and define mixed phase and ice crystal conditions. New proposed Sec.
25.1324 includes an icing requirement for angle of attack systems. This
would be similar to the icing requirements for airspeed indication
systems. The proposed section would require the angle of attack system
to be heated to prevent malfunction in appendices C and O icing
conditions and in the mixed phase and ice crystal conditions defined in
Sec.  25.1323.
---------------------------------------------------------------------------

    \16\ 14 CFR 25.773, 25.1323, and 25.1325.
---------------------------------------------------------------------------

    In the proposed revisions to the requirements for pilot compartment
view, airspeed indication system, and static pressure system,\17\ and
the new proposed requirements for angle of attack systems, an airplane
certified in accordance with Sec.  25.1420(a)(1) or (a)(2) would not be
required to be evaluated for all of appendix O. For airplanes certified
in accordance with Sec.  25.1420(a)(1), the icing conditions that the
airplane is certified to safely exit following detection must be
considered. For airplanes certified in accordance with Sec.
25.1420(a)(2), the icing conditions that the airplane is certified to
safely operate in, and to safely exit following detection, must be
considered. For airplanes certified in accordance with Sec.
25.1420(a)(3) and for airplanes not subject to Sec.  25.1420, all icing
conditions must be considered. Airplanes not certified for flight in
icing need not consider appendix O.
---------------------------------------------------------------------------

    \17\ Ibid.
---------------------------------------------------------------------------

    The engine induction system icing section (Sec.  25.1093) and
propeller deicing section (Sec.  25.929) contain requirements for
operation in icing conditions. As a conservative approach to ensure
safe operation of an airplane in an inadvertent encounter with icing,
the existing language in Sec.  25.1093 contains requirements for
operation in icing conditions, even for an airplane that is not
approved for flight in icing. Since proposed appendix O defines icing
conditions that also may be inadvertently encountered, Sec.  25.1093
would be revised to reference appendix O in its entirety. This would
maintain the FAA's conservative approach for this section. Section
25.929 (propeller deicing) would also be revised to reference appendix
O in its entirety.
    Sections 25.929 and 25.1323 generically reference icing instead of
specifically mentioning appendix C. Historically, the icing conditions
specified in appendix C have been applied to these rules. For clarity,
we are revising Sec. Sec.  25.929 and 25.1323 so they specifically
reference appendix C, as well as appendix O. The proposed revisions to
icing regulations for pilot compartment view, propellers, engine
induction system icing protection, airspeed indication system, static
pressure system, and angle of attack system would be applicable to all
transport category airplanes to ensure safe operation during operations
in icing conditions.
    The proposed revisions to Sec.  25.903 would retain the existing
regulations and add new subparagraphs to be consistent with the
proposed part 33 changes in Sec.  33.68. These revisions would allow
for approving new aircraft type certification programs with engines
certified to earlier amendment levels. The proposed revisions would
make it clear that the proposed part 33 changes would not be
retroactively imposed on an already type certified engine design,
unless service history indicated that an unsafe condition was present.
    The proposed revision to Sec.  25.929 clarifies the meaning of the
words ``for airplanes intended for use where icing may be expected.''
The intent has been for the rule to be applicable to airplanes
certified for flight in icing.

Engine and Engine Installation Requirements

    The proposed revisions to Sec. Sec.  25.1093, 33.68, and 33.77
would change the icing environmental requirements used to evaluate
engine protection and operation in icing conditions. The reason for
these changes is that the incident history of some airplanes has shown
that the current icing environmental requirements are inadequate. The
effect of the change would be to require an evaluation of safe
operation in the revised icing environment. The proposed revision to
Sec.  25.1093 restructures paragraph (b) and adds a new Table 1--Icing
Conditions for Ground Tests. The proposed rules would require engines
and engine installations to operate safely throughout the SLD
conditions defined in proposed new part 25, appendix O, and the newly
defined mixed phase and ice crystal conditions defined in proposed new
part 33, appendix D.\18\ The proposed appendix D was developed by the
ARAC Engine Harmonization Working Group and the Power Plant
Installation Harmonization Working Group, which included meteorologists
and icing research specialists from industry, FAA/FAA Tech Center,
Meteorological Services of Canada, National Aeronautics and Space
Administration (NASA), and Transport Canada/Transport Development
Center. The ARAC recommended appendix D and the FAA concurs with the
recommendation.
---------------------------------------------------------------------------

    \18\ See FAA report DOT/FAA/AR-09/13, Technical Compendium from
Meetings of the Engine Harmonization Working Group, March 2009 for
details on appendix D and its development.
---------------------------------------------------------------------------

    The proposed revision to Sec.  25.1521 would retain the existing
regulations and add a new subparagraph that would require an additional
operating limitation for turbine engine installations during ground
operation in icing conditions defined in Sec.  25.1093(b)(2). That
operating limitation would address the maximum time interval between
any engine run-ups from idle and the minimum ambient temperature
associated with that run-up interval. This limitation is necessary
because we do not currently have any specific requirements for run-up
procedures for engine ground operation in icing conditions. The engine
run-up procedure, including the maximum time interval between run-ups
from idle, run-up power setting, duration at power, and the minimum
ambient temperature demonstrated for that run-up interval proposed in
Sec.  25.1521, would be included in the Airplane Flight Manual in
accordance with existing Sec.  25.1581(a)(1) and Sec.  25.1583(b)(1).
    The engine run-up procedure from ground idle to a moderate power or
thrust setting is necessary to shed ice build-up on the fan blades
before the quantity of ice reaches a level that could adversely affect
engine operation if ice is shed into the engine. The proposed revision
to Sec.  25.1521 would not require additional testing. The ice shedding
demonstration may be included as part of the Sec.  33.68 engine icing
testing.

Operating Limitations

    The proposed revision to Sec.  25.1533 would establish an operating
limitation applicable to airplanes that are not certified in accordance
with proposed Sec.  25.1420(a)(1) or (a)(2). The flightcrews of these
airplanes would be required to exit all icing conditions if they
encounter appendix O icing conditions that the airplane has not been
certified to operate in.

Expansion of Proposed Icing Requirements

    The proposed regulations \19\ for the airspeed indicating system
and angle of

attack system would address the operation of those systems in specific
mixed phase and ice crystal conditions, as defined in proposed Appendix
O. During the drafting of this NPRM the FAA became aware of airspeed
indicating system malfunctions in environmental conditions that may not
be addressed by these proposed regulations. The FAA is reviewing the
malfunctions and is considering the need to change the proposed mixed
phase and ice crystal parameters to include freezing rain. The maximum
mixed phase and ice crystal parameters that we are considering are
those defined in the proposed part 33, appendix D. The freezing rain
parameters that we are considering are based on standards some
manufacturers have used for airdata probes. The maximum freezing rain
parameters that we are considering are:
---------------------------------------------------------------------------

    \19\ 14 CFR 25.1323, and 25.1324.

----------------------------------------------------------------------------------------------------------------
Static air temperature                          Altitude range               Liquid                      Droplet
                                                                              water                          MVD
                                                                            content  Horizontal extent
----------------------------------------------------------------------------------------------------------------
([deg]C)                                          (ft)             (m)       (g/m3)    (km)   (nmiles)  ([micro]
                                                                                m)
----------------------------------------------------------------------------------------------------------------
-2 to 0...............................     0 to 10 000       0 to 3000            1     100         50      1000
                                                                                6       5          3      2000
                                                                                15       1        0.5      2000
----------------------------------------------------------------------------------------------------------------

    We consider the mixed phase and ice crystal parameters defined in
the proposed part 33, appendix D, plus the freezing rain parameters
defined above to be adequate to prevent potential airspeed indicating
system malfunctions in these newly defined environmental conditions. We
request technical and economic comments on whether the proposed
airspeed indicating system and angle of attack system regulations
should include these expanded parameters. Based on comments we receive,
we may add these parameters to the final rule.

Differences From the ARAC Recommendations

    The IPHWG recommended changes to parts 25 and 33 to ensure the safe
operation of airplanes and engines in icing conditions. The FAA concurs
with the recommendations, but has determined it is necessary to revise
to which airplanes the new airplane icing certification requirements in
the proposed Sec.  25.1420 would apply. The proposed Sec.  25.1420 in
this NPRM would apply to airplanes with either: (1) a takeoff maximum
gross weight of less than 60,000 lbs (27,000 kg), or (2) reversible
flight controls. An airplane with reversible flight controls in any
axis (pitch, roll, or yaw), even if these flight controls are
aerodynamically boosted and/or power-assisted, would be considered to
have reversible flight controls under this proposed rule. An airplane
with flight controls that are irreversible under normal operating
conditions, but are reversible following a failure, would not be
considered to have reversible flight controls under this proposed rule.
Reversible, aerodynamically boosted, and power-assisted flight controls
are defined in Appendix 1 to the preamble of this NPRM. The ADs
described above in section B. ``Prior FAA Actions to address the Safety
Concern'' are only applicable to airplanes equipped with both
reversible flight controls in the roll axis and pneumatic deicing
boots.
    A group of IPHWG members (Boeing, Airbus, and Embraer, supported by
Cessna) held a minority position in their belief that the applicability
of the proposed Sec.  25.1420 should exclude airplanes with certain
design features. Their rationale for the position is that large
transport airplanes still in production have not experienced any
accidents or serious incidents as a result of flying in SLD icing
conditions. These manufacturers proposed that airplanes having all
three of the following design features should be excluded from
compliance with Sec.  25.1420:
    (1) Gross weight in excess of 60,000 lbs (27,000 kg);
    (2) Irreversible powered flight controls; and
    (3) Wing leading-edge high-lift devices.
    These manufacturers included the gross weight criterion in this
list, in part, because size has a direct bearing on an airplane's
susceptibility to the adverse effects of ice accretion. The size of an
airplane determines the sensitivity of its flight characteristics to
ice thickness and roughness. The relative effect of a given ice height
(or ice roughness height) decreases as airplane size increases.
    The irreversible powered flight controls design feature was chosen,
in part, because using irreversible powered flight controls reduces an
airplane's susceptibility to SLD conditions. The concern that SLD
accretions can produce hinge moment or other anomalous control force/
trim effects is not applicable to those systems.
    The wing leading-edge high-lift devices design feature was chosen,
in part, because, for wings without ice contamination, those devices
provide a considerable increase in the maximum lift coefficient (CLmax)
compared to fixed leading edges. When wings equipped with those devices
are contaminated with ice, they have smaller relative CLmax losses due
to ice accretion than wings with fixed leading edges.
    The IPHWG majority (Air Line Pilots Association, International
(ALPA), Civil Aviation Authority for the United Kingdom (CAA/UK), FAA/
FAA Tech Center, Meteorological Services of Canada, National
Aeronautics and Space Administration (NASA), SAAB, Transport Canada/
Transport Development Center) did not accept the exclusion of airplanes
with the three aforementioned design features because one cannot
predict with confidence that the past service experience of airplanes
with these specific design features will be applicable to future
designs. The IPHWG majority recommended applying the new SLD airplane
certification requirements proposed in the new Sec.  25.1420 to all
future transport category airplane type designs.
    The IPHWG majority opposed limiting the applicability of the rule
based on airplane gross weight, in part, because the ratio of wing and
control surface sizes to airplane weight varies between airplane
designs. Therefore, airplane takeoff weight is not a consistent
indicator of lifting and control surface size or chord, which are the
important parameters affecting sensitivity to a given ice accretion.
    Excluding airplanes with irreversible flight controls was opposed,
in part, because hinge moment and other anomalous control forces are
not the only concern in SLD icing conditions. An irreversible control
surface may not be deflected by the SLD accumulation but the
aerodynamic efficiency of the control is likely to be degraded by the
presence of SLD icing in front of the control surface.
    Excluding airplanes with wing leading edge high-lift devices was
opposed, in part, because there are many different designs for such
devices, which may not all be equally effective

in mitigating the negative effects of SLD ice accretions. The designs
for those devices include:
     Slats that may be slotted or sealed to the basic wing
leading edge, over or under deflected, with deflection and slotting
that may be automated as a function of stall warning or airplane angle
of attack;
     Krueger flaps that may be slotted or sealed to the wing
leading edge, flexed to optimum curvature or conformed to the wing's
leading edge lower surface; and
     Vortilons or some other vortex creating devices.
    In addition, for transport category airplanes with leading edge
high-lift devices, the spanwise extent of ice protection varies from
100 percent for some early turbo-jet airplane slats, to the span of two
slats for later airplane designs, to none for Krueger flaps. The
variations in the designs lead to varying degrees of aerodynamic
benefit. Without defining the specific performance benefits associated
with the above designs, the potential safety margins for SLD conditions
cannot be determined.
    The complete minority and majority positions are discussed in the
working group report, which is available in the public docket.\20\
---------------------------------------------------------------------------

    \20\ The complete IPHWG working group report is available on the
Internet at http://regulations.gov. A copy will also be placed in
the docket (FAA-2010-0636).
---------------------------------------------------------------------------

    In order to propose a rule with the estimated costs commensurate
with the estimated benefits, the FAA determined the applicability of
the proposed rule should be limited based on service histories of
certified airplanes, and the assumption that similar future designs
will continue to not experience the safety problems addressed by this
proposal. Therefore, the FAA decided to revise the IPHWG rulemaking
recommendation by incorporating, in part, the IPHWG minority position
to exclude airplanes with certain design features.
    The FAA continues to agree with the IPHWG majority position that
the presence (or conversely, the absence) of leading edge high lift
devices should not be used as a basis for determining the applicability
of the proposed Sec.  25.1420. There is insufficient data to conclude
either that every type of leading edge high lift device, or that a
specific leading edge high lift device design will affect (positively
or negatively) an airplane's ability to operate in SLD atmospheric
icing conditions. Also, leading edge high lift devices are only
deployed in certain phases of flight (for example, takeoff and
landing), and their deployment may differ for different flap
configurations. For example, a leading edge slat may be sealed in one
flap configuration, but slotted (that is, with a gap opened up between
the trailing edge of the slat and the wing) in others. Therefore, the
applicability of the proposed Sec.  25.1420 is not affected by the
presence or absence of leading edge high lift devices.
    We request comment on whether this proposed rule, if adopted,
should be applied to airplanes larger than 60,000 pounds MTOW or
airplanes with other design features whose presence or absence would
result in the airplane being susceptible to safety problems while
operating in the SLD icing conditions defined in the proposed appendix
O, as well as the economic analysis associated with these
decisions.\21\
---------------------------------------------------------------------------

    \21\ A copy of the Initial Regulatory Evaluation (dated October
5, 2009) can be found in the docket (FAA-2010-0636).
---------------------------------------------------------------------------

    This NPRM also differs from the ARAC recommendation by proposing a
revision to Sec.  25.1533 for airplanes not certified to operate in all
of the SLD atmospheric icing conditions specified in the proposed new
appendix O (that is, airplanes certified in accordance with proposed
Sec.  25.1420(a)(1) or (a)(2)). The proposal would establish an
operating limitation that requires the flightcrews to exit all icing
conditions if they encounter appendix O icing conditions in which the
airplane has not been certified to operate.
    Another difference between this NPRM and the ARAC recommendation
concerns an ARAC recommendation to establish separate stall warning
margin and controllability requirements using the ice accretion
associated with detection of appendix O icing conditions that require
exiting all icing conditions. For airplanes that require exiting all
icing conditions after encountering certain appendix O icing
conditions, the ARAC recommended (and the FAA proposes in this NPRM)
stall warning margin and controllability requirements that must be met
with the ice accretion existing at the time the airplane exits all
icing conditions. The ARAC was concerned that some future airplanes
would be incapable of complying with these recommended requirements
without including some means to increase the stall warning margin and
airplane controllability upon detection of appendix O icing conditions.
The ARAC recommended applying less stringent stall warning and
controllability requirements with the ice accretion existing at the
time appendix O icing conditions are detected, before the means to
increase the stall warning margin and airplane controllability becomes
effective.
    The FAA considers these ARAC recommended requirements to add
significant complexity to the proposed rule to address an issue that
may not arise. The FAA considers it unlikely that future airplane
designs will include means to increase the stall warning margin and
airplane controllability upon detection of appendix O icing conditions
in addition to the means that are incorporated in many current
transport category airplane designs to change the stall warning device
activation point upon activation of the ice protection system.
Therefore, these ARAC recommendations are not included in this NPRM. If
needed, the FAA can issue special conditions, in accordance with Sec.
21.16, to provide adequate safety standards in the unlikely event that
such design features are included in a future transport category
airplane.
    Another difference between this NPRM and the ARAC recommendation
concerns the requirements for pilot compartment view, airspeed
indication system, angle of attack system and static pressure
system.\22\ For these rules the ARAC recommendation would have required
airplanes certified in accordance with Sec.  25.1420(a)(1) or (a)(2) to
consider all appendix O icing conditions. However, the ARAC recommended
advisory circular material allowed these airplanes to consider less
than the full appendix O icing conditions. The FAA is not proposing
that these airplanes must meet the performance and handling qualities
requirements for all of the icing conditions specified in appendix O.
Therefore, for pilot compartment view, airspeed indication system,
angle of attack system and static pressure system,\23\ the agency
concurs that it would only be necessary to show compliance under the
applicable conditions in appendix O.
---------------------------------------------------------------------------

    \22\ 14 CFR 25.773, 25.1323, 25.1324, and 25.1325.
    \23\ Ibid.
---------------------------------------------------------------------------

Discussion of Working Group Non-Consensus Issues

    One goal of the ARAC process is to have a working group achieve
consensus on all of the recommendations. The IPHWG did not unanimously
agree on the following issues:
    1. Whether it is necessary to flight test in natural SLD icing
conditions.
    2. Whether airplanes with certain design features should be exempt
from the recommendation for Sec.  25.1420.

    3. Whether it is acceptable to certificate an airplane to a portion
of appendix O, as proposed in the recommendation for Sec.
25.1420(a)(2).
    4. Whether certain icing related accidents might have been
prevented if an accident airplane had complied with the recommendations
in the IPHWG report.
    A detailed discussion of the IPHWG's minority and majority opinions
on these issues is included in the working group report. A copy of the
working group report is in the public docket.\24\
---------------------------------------------------------------------------

    \24\ The complete IPHWG working group report is available on the
Internet at http://regulations.gov. The docket number is FAA-2010-
0636.
---------------------------------------------------------------------------

    The FAA predominantly concurred with the ARAC's recommendations,
but determined it was necessary to revise the applicability of the
recommendation for Sec.  25.1420, as discussed previously.

Paperwork Reduction Act

    The Paperwork Reduction Act of 1995 (44 U.S.C. 3507(d)) requires
that the FAA consider the impact of paperwork and other information
collection burdens imposed on the public. The information collection
requirements associated with this NPRM have been previously approved by
the Office of Management and Budget (OMB) under the provisions of the
Paperwork Reduction Act of 1995 (44 U.S.C. 3507(d)) and have been
assigned OMB Control Number 2120-0018.

International Compatibility

    In keeping with U.S. obligations under the Convention on
International Civil Aviation, it is FAA policy to comply with
International Civil Aviation Organization (ICAO) Standards and
Recommended Practices to the maximum extent practicable. The FAA has
determined that there are no ICAO Standards and Recommended Practices
that correspond to these proposed regulations.

European Aviation Safety Agency

    The European Aviation Safety Agency (EASA) was established by the
European Community to develop standards to ensure safety and
environmental protection, oversee uniform application of those
standards, and promote them internationally. EASA formally became
responsible for certification of aircraft, engines, parts, and
appliances on September 28, 2003. EASA has a project similar to SLD on
its rulemaking inventory and our intent is to harmonize these
regulations.

Regulatory Evaluation, Regulatory Flexibility Determination,
International Trade Analysis, and Unfunded Mandates

    Changes to Federal regulations must undergo several economic
analyses. First, Executive Order 12866 directs that each Federal agency
shall propose or adopt a regulation only upon a reasoned determination
that the benefits of the intended regulation justify its costs. Second,
the Regulatory Flexibility Act of 1980 (Pub. L. 96-354) requires
agencies to analyze the economic impact of regulatory changes on small
entities. Third, the Trade Agreements Act (Pub. L. 96-39) prohibits
agencies from setting standards that create unnecessary obstacles to
the foreign commerce of the United States. In developing U.S.
standards, this Trade Act requires agencies to consider international
standards and, where appropriate, that they be the basis of U.S.
standards. Fourth, the Unfunded Mandates Reform Act of 1995 (Pub. L.
104-4) requires agencies to prepare a written assessment of the costs,
benefits, and other effects of proposed or final rules that include a
Federal mandate likely to result in the expenditure by State, local, or
tribal governments, in the aggregate, or by the private sector, of $100
million or more annually (adjusted for inflation with base year of
1995). This portion of the preamble summarizes the FAA's analysis of
the economic impacts of this proposed rule. We suggest readers seeking
greater detail read the full regulatory evaluation, a copy of which we
have placed in the docket for this rulemaking.
    In conducting these analyses, FAA has determined that this proposed
rule: (1) Has benefits that justify its costs; (2) is not an
economically ``significant regulatory action'' as defined in section
3(f) of Executive Order 12866; (3) is ``significant'' as defined in
DOT's Regulatory Policies and Procedures; (4) would not have a
significant economic impact on a substantial number of small entities;
(5) would not create unnecessary obstacles to the foreign commerce of
the United States; and (6) would not impose an unfunded mandate on
State, local, or tribal governments, or on the private sector by
exceeding the threshold identified above. These analyses are summarized
below.

Total Benefits and Costs of This Rule

    This NPRM would amend the airworthiness standards applicable to
certain transport category airplanes certified for flight in icing
conditions and the icing airworthiness standards applicable to certain
aircraft engines. The affected fleet and categories of benefits and
costs are customized to the requirements contained in this proposal.
So, depending on the category and type of airplane, the benefits and
costs are analyzed over different time periods. It is important for the
reader to focus on present value benefits and costs. The total
estimated benefits are $405.6 million ($99.5 million present value).
The total estimated costs are $71.0 million ($54.0 million present
value). On an annualized basis, for the time period 2012-2064, the
benefits are $7.0 million, and the costs are $3.8 million. Therefore,
the benefits of the proposed rule justify the costs, and the proposed
rule is cost beneficial.

Persons Potentially Affected by This Rule

     Part 25 airplane manufacturers.
     Engine manufacturers.
     Operators of Affected Equipment.

Assumptions

     Discount rate--7%.
     Costs and benefits are expressed in 2009 dollars and that
both costs and benefits start to occur in 2011. We conservatively
assume that all certifications are approved one year after the rule is
codified (2011), and that production/deliveries begin to occur the
following year (2012). Airplane deliveries continue to accumulate until
the airplane is out of production and then begin to retire in the 25th
year of service. We have customized different fleet types (smaller,
medium, larger) based upon the actual historical production cycles and
deliveries. The varying periods are based on all the historical data
that we have available. The production cycles for smaller airplanes are
shorter than the production cycles of larger airplanes, thus the
differing time periods.
     Value of an Averted Fatality--$6.0 million.
     Fuel Cost per gallon--$1.92.

Benefits of This Proposed Rule

    The industry, with the FAA, analyzed the SLD events for part 25
certified airplanes. We evaluated the events for applicability and
preventability in context with the requirements contained in this
proposed rule.
    First, we develop an annual risk of a catastrophic SLD event per
aircraft and assume a uniform annual likelihood. Next, we multiply the
total annual affected aircraft by the annual risk per aircraft. Lastly,
we multiply the total annual risk by the estimated cost of an average
SLD event. When summed over time, the total estimated benefits are

$405.6 million ($99.5 million present value).

Costs of This Proposed Rule

    The total estimated costs are $71.0 million ($54.0 million present
value). We obtained the basis of our cost estimates from the industry.
The manufacturers used accompanying advisory circulars (AC) describing
acceptable means for showing compliance. The compliance costs are
analyzed in context of the part 25 and part 33 certification
requirements.
    The FAA originally asked ARAC to estimate other operational costs
beyond the additional hardware and fuel consumption costs. The
additional hardware costs would be for SLD ice detectors that
manufacturers would install to be in compliance with the proposed
requirements. The additional hardware costs would be accompanied by
additional fuel consumption costs from the accompanying weight changes
due to the SLD ice detectors. Accordingly, ARAC provided this data to
the FAA. However, as we neared completion of our cost analysis for
these requirements, we queried individual operators and they informed
us that they were already in compliance and there were no additional
operational costs beyond fuel and hardware.
    As summarized below, the cost categories in the regulatory
evaluation incorporate both certification and operational costs. We
analyze each cost category separately. The cost categories in this
evaluation are the same as those provided by industry to comply with
the requirements contained in this proposal. For this analysis, the
estimated costs were:

------------------------------------------------------------------------
                                       Nominal Cost         PV Cost
------------------------------------------------------------------------
Engine Cert Cost..................         $7,936,000         $6,931,610
Engine Capital Cost...............          6,000,000          5,240,632
Total Engine......................         13,936,000         12,172,242
Small Aircraft Certification Cost.         24,999,039         21,835,129
New Large Aircraft Certification            3,154,600          2,755,350
 Cost.............................
Amended Type Certificate Large             10,438,800          9,117,652
 Airplane Certification Cost......
Hardware Costs....................         10,390,000          5,842,024
Fuel Burn All.....................          8,046,676          2,261,941
                                   -------------------------------------
    Total.........................         70,965,115         53,984,338
------------------------------------------------------------------------

Alternatives Considered

    Alternative 1--Make all sizes of aircraft applicable to the
proposal. Not all the requirements in this proposal extend to larger
transport category aircraft (those with a maximum takeoff weight
greater than 60,000 pounds). Under this alternative, the proposed
design requirements would extend to all transport category aircraft.
This alternative was rejected because this alternative would add
significant cost without a commensurate increase in benefits.
    Alternative 2--Limit the scope of applicability to small aircraft.
Although this alternative would decrease the estimated cost, the FAA
believes that medium airplanes have the same risk as small airplanes.
The FAA does not want a significant proportion of the future fleet to
be disproportionately at risk.

Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (Pub. L. 96-354) (RFA)
establishes ``as a principle of regulatory issuance that agencies shall
endeavor, consistent with the objectives of the rule and of applicable
statutes, to fit regulatory and informational requirements to the scale
of the businesses, organizations, and governmental jurisdictions
subject to regulation. To achieve this principle, agencies are required
to solicit and consider flexible regulatory proposals and to explain
the rationale for their actions to assure that such proposals are given
serious consideration.'' The RFA covers a wide-range of small entities,
including small businesses, not-for-profit organizations, and small
governmental jurisdictions.
    Agencies must perform a review to determine whether a rule will
have a significant economic impact on a substantial number of small
entities. If the agency determines that it will, the agency must
prepare a regulatory flexibility analysis as described in the RFA.
    However, if an agency determines that a rule is not expected to
have a significant economic impact on a substantial number of small
entities, section 605(b) of the RFA provides that the head of the
agency may so certify and a regulatory flexibility analysis is not
required. The certification must include a statement providing the
factual basis for this determination, and the reasoning should be
clear. Based on the analysis presented below, we determined there would
not be a significant impact on a substantial number of small entities.

Airplane and Engine Manufacturers

    Aircraft and Engine Manufacturers would be affected by the
requirements contained in this proposal.
    For aircraft manufacturers, we use the size standards from the
Small Business Administration for Air Transportation and Aircraft
Manufacturing specifying companies having less than 1,500 employees as
small entities. The current United States part 25 airplane
manufacturers include: Boeing, Cessna Aircraft, Gulfstream Aerospace,
Learjet (owned by Bombardier), Lockheed Martin, McDonnell Douglas (a
wholly-owned subsidiary of The Boeing Company), Raytheon Aircraft, and
Sabreliner Corporation. Because all U.S. transport-aircraft category
manufacturers have more than 1,500 employees, none are considered small
entities.
    United States aircraft engine manufacturers include: General
Electric, CFM International, Pratt & Whitney, International Aero
Engines, Rolls-Royce Corporation, Honeywell, and Williams
International. All but one exceeds the Small Business Administration
small-entity criteria for aircraft engine manufacturers. Williams
International is the only one of these manufacturers that is a U.S.
small business. One small entity is not a substantial number.

Operators

    In addition to the certification cost incurred by manufacturers,
operators would incur fuel costs due to the estimated additional impact
of weight changes from equipment on affected airplanes. On average, an
affected airplane would incur additional fuel costs of roughly $525 per
year.
    Because this proposed rule would apply to airplanes that have yet
to be designed, there would be no immediate cost to small entities.
However, as of 2007, there are at least 54 small entity operators with
1,500 or fewer employees who would qualify as small entities.

    According to the ``Airliner Price Guide,'' the average cost of a
new aircraft that would incur such expenses is approximately $17
million. The corresponding 3-year average total aircraft operating
expenses on an affected per airplane basis was $758,000. The estimated
additional cost of $525 would add only 0.07% to the total annual
operating expenses. We do not consider this a significant economic
impact.
    Because this proposed rule would not have a significant economic
impact on a substantial number of airplane manufacturers, engine
manufacturers or operators, the FAA certifies that this proposed rule
would not have a significant economic impact on a substantial number of
small entities. The FAA solicits comments regarding this determination.

International Trade Analysis

    The Trade Agreements Act of 1979 (Pub. L. 96-39), as amended by the
Uruguay Round Agreements Act (Pub. L. 103-465), prohibits Federal
agencies from establishing standards or engaging in related activities
that create unnecessary obstacles to the foreign commerce of the United
States. Pursuant to these Acts, the establishment of standards is not
considered an unnecessary obstacle to the foreign commerce of the
United States, so long as the standard has a legitimate domestic
objective, such the protection of safety, and does not operate in a
manner that excludes imports that meet this objective. The statute also
requires consideration of international standards and, where
appropriate, that they be the basis for U.S. standards.
    The FAA has assessed the potential effect of this proposed rule and
determined that it would impose the same costs on domestic and
international entities and thus has a neutral trade impact.

Unfunded Mandates Assessment

    Title II of the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-
4) requires each Federal agency to prepare a written statement
assessing the effects of any Federal mandate in a proposed or final
agency rule that may result in an expenditure of $100 million or more
(in 1995 dollars) in any one year by State, local, and tribal
governments, in the aggregate, or by the private sector; such a mandate
is deemed to be a ``significant regulatory action.'' The FAA currently
uses an inflation-adjusted value of $143.1 million in lieu of $100
million. This proposed rule does not contain such a mandate; therefore,
the requirements of Title II do not apply.

Executive Order 13132, Federalism

    The FAA has analyzed this proposed rule under the principles and
criteria of Executive Order 13132, Federalism. We determined that this
action would not have a substantial direct effect on the States, on the
relationship between the national Government and the States, or on the
distribution of power and responsibilities among the various levels of
government, and, therefore, would not have federalism implications.

Regulations Affecting Intrastate Aviation in Alaska

    Section 1205 of the FAA Reauthorization Act of 1996 (110 Stat.
3213) requires the Administrator, when modifying regulations in Title
14 of the CFR in a manner affecting intrastate aviation in Alaska, to
consider the extent to which Alaska is not served by transportation
modes other than aviation, and to establish appropriate regulatory
distinctions. Because this proposed rule would apply to the
certification of future designs of transport category airplanes and
their subsequent operation, it could, if adopted, affect intrastate
aviation in Alaska. The FAA, therefore, specifically requests comments
on whether there is justification for applying the proposed rule
differently in intrastate operations in Alaska.

Environmental Analysis

    FAA Order 1050.1E identifies FAA actions that are categorically
excluded from preparation of an environmental assessment or
environmental impact statement under the National Environmental Policy
Act in the absence of extraordinary circumstances. The FAA has
determined this proposed rulemaking action qualifies for the
categorical exclusion identified in paragraph 4(j) and involves no
extraordinary circumstances.

Regulations That Significantly Affect Energy Supply, Distribution, or
Use

    The FAA has analyzed this NPRM under Executive Order 13211, Actions
Concerning Regulations that Significantly Affect Energy Supply,
Distribution, or Use (May 18, 2001). We have determined that it is not
a ``significant energy action'' under the executive order because,
while it is a ``significant regulatory action,'' it is not likely to
have a significant adverse effect on the supply, distribution, or use
of energy.

Plain English

    Executive Order 12866 (58 FR 51735, Oct. 4, 1993) requires each
agency to write regulations that are simple and easy to understand. We
invite your comments on how to make these proposed regulations easier
to understand, including answers to questions such as the following:
     Are the requirements in the proposed regulations clearly
stated?
     Do the proposed regulations contain unnecessary technical
language or jargon that interferes with their clarity?
     Would the regulations be easier to understand if they were
divided into more (but shorter) sections?
     Is the description in the preamble helpful in
understanding the proposed regulations?
    Please send your comments to the address specified in the ADDRESSES
section of this preamble.

Additional Information

Comments Invited

    The FAA invites interested persons to participate in this
rulemaking by submitting written comments, data, or views. We also
invite comments relating to the economic, environmental, energy, or
federalism impacts that might result from adopting the proposals in
this document. The most helpful comments reference a specific portion
of the proposal, explain the reason for any recommended change, and
include supporting data. To ensure the docket does not contain
duplicate comments, please send only one copy of written comments, or
if you are filing comments electronically, please submit your comments
only one time.
    We will file in the docket all comments we receive, as well as a
report summarizing each substantive public contact with FAA personnel
concerning this proposed rulemaking. Before acting on this proposal, we
will consider all comments we receive on or before the closing date for
comments. We will consider comments filed after the comment period has
closed if it is possible to do so without incurring expense or delay.
We may change this proposal in light of the comments we receive.

Proprietary or Confidential Business Information

    Do not file in the docket information that you consider to be
proprietary or confidential business information. Send or deliver this
information directly to the person identified in the FOR FURTHER
INFORMATION CONTACT section of this document. You must mark the
information that you consider

proprietary or confidential. If you send the information on a disk or
CD ROM, mark the outside of the disk or CD ROM and also identify
electronically within the disk or CD ROM the specific information that
is proprietary or confidential.
    Under 14 CFR 11.35(b), when we are aware of proprietary information
filed with a comment, we do not place it in the docket. We hold it in a
separate file to which the public does not have access, and we place a
note in the docket that we have received it. If we receive a request to
examine or copy this information, we treat it as any other request
under the Freedom of Information Act (5 U.S.C. 552). We process such a
request under the DOT procedures found in 49 CFR part 7.

Availability of Rulemaking Documents

    You can get an electronic copy of rulemaking documents using the
Internet by--
    1. Searching the Federal eRulemaking Portal (http://
www.regulations.gov);
    2. Visiting the FAA's Regulations and Policies web page at http://
www.faa.gov/regulations_policies/; or
    3. Accessing the Government Printing Office's web page at http://
www.gpoaccess.gov/fr/index.html.
    You can also get a copy by sending a request to the Federal
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence
Avenue, SW., Washington, DC 20591, or by calling<PHONE_NUMBER>. Make
sure to identify the docket number or notice number of this rulemaking.
    You may access all documents the FAA considered in developing this
proposed rule, including economic analyses and technical reports, from
the internet through the Federal eRulemaking Portal referenced in
paragraph (1).
    The following appendix will not appear in the Code of Federal
Regulations.

Appendix 1 to the Preamble--Definition of Terms Used in This Preamble

    For the purposes of this preamble, the following definitions are
applicable. These definitions of terms are intended for use only with
this preamble:
    a. Appendix C Icing Conditions: The environmental conditions
defined in appendix C of 14 CFR part 25.
    b. Appendix O Icing Conditions: The environmental conditions
defined in appendix O of 14 CFR part 25.
    c. Drizzle Drop: A drop of water measuring 100 [micro]m to 500
[micro]m (0.1-0.5 mm) in diameter.
    d. Freezing Drizzle (FZDZ): Supercooled drizzle drops that remain
in liquid form and freeze upon contact with objects colder than
0[deg]C.
    e. Freezing Rain (FZRA): Supercooled rain drops that remain in
liquid form and freeze upon contact with objects colder than 0[deg]C.
    f. Icing Conditions: The presence of atmospheric moisture and
temperature conducive to airplane icing.
    g. Icing Conditions Detector: A device that detects the presence of
atmospheric moisture and temperature conducive to airplane icing.
    h. Irreversible Flight Controls: Flight controls in the normal
operating configuration that have loads generated at the control
surfaces of an airplane which are reacted against the actuator and its
mounting and cannot be transmitted directly back to the flight deck
controls. This term refers to flight controls in which all of the force
necessary to move the pitch, roll, or yaw control surfaces is provided
by hydraulic or electric actuators, the motion of which is controlled
by signals from the flight deck controls.
    i. Liquid Water Content (LWC): The total mass of water contained in
liquid drops within a unit volume or mass of air, usually given in
units of grams of water per cubic meter (g/m\3\).
    j. Mean Effective Diameter (MED): The calculated drop diameter that
divides the total liquid water content present in the drop size
distribution in half. Half the water volume will be in larger drops and
half the volume in smaller drops. This value is calculated, as opposed
to being arrived at by measuring actual drop size. The MED is based on
an assumed Langmuir drop size distribution. The fact that it is a
calculated measurement is how it differs from median volume diameter,
which is based on actual drop size.
    k. Median Volume Diameter (MVD): The drop diameter that divides the
total liquid water content present in the drop distribution in half.
Half the water volume will be in larger drops and half the volume in
smaller drops. The value is obtained by actual drop size measurements.
    l. Mixed Phase Icing Environment: A combination of supercooled
liquid and ice crystals.
    m. Rain Drop: A drop of water greater than 500 [micro]m (0.5 mm) in
diameter.
    n. Reversible Flight Controls: Flight controls in the normal
operating configuration that have force or motion originating at the
airplane's control surface (for example, through aerodynamic loads,
static imbalance, or trim tab inputs) that is transmitted back to
flight deck controls. This term refers to flight deck controls
connected to the pitch, roll, or yaw control surfaces by direct
mechanical linkages, cables, or push-pull rods in such a way that pilot
effort produces motion or force about the hinge line.
    (1) Aerodynamically boosted flight controls: Reversible flight
control systems that employ a movable tab on the trailing edge of the
main control surface linked to the pilot's controls or to the structure
in such a way as to produce aerodynamic forces that move, or help to
move, the surface. Among the various forms are flying tabs, geared or
servo tabs, and spring tabs.
    (2) Power-assisted flight controls: Reversible flight control
systems in which some means is provided, usually a hydraulic actuator,
to apply force to a control surface in addition to that supplied by the
pilot to enable large surface deflections to be obtained at high
speeds.
    o. Supercooled Large Drops (SLD): Supercooled liquid water that
includes freezing rain or freezing drizzle.
    p. Supercooled Water: Liquid water at a temperature below the
freezing point of 0[deg]C.

List of Subjects

14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping
requirements, Safety, Transportation.

14 CFR Part 33

    Aircraft, Aviation safety.

The Proposed Amendment

    In consideration of the foregoing, the Federal Aviation
Administration proposes to amend Chapter I of Title 14, Code of Federal
Regulations parts 25 and 33 as follows:

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

    1. The authority citation for part 25 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702 and 44704.

    2. Amend Sec.  25.21 by revising paragraphs (g)(1) and (g)(2) and
adding paragraphs (g)(3) and (g)(4) to read as follows:

Sec.  25.21  Proof of compliance.

* * * * *
    (g) * * *
    (1) Paragraphs (g)(3) and (g)(4) of this section apply only to
airplanes with one or both of the following attributes:
    (i) Takeoff maximum gross weight is less than 60,000 lbs; or
    (ii) The airplane is equipped with reversible flight controls.

    (2) Each requirement of this subpart, except Sec. Sec.  25.121(a),
25.123(c), 25.143(b)(1) and (2), 25.149, 25.201(c)(2), 25.207(c) and
(d), 25.239, and 25.251(b) through (e), must be met in the icing
conditions specified in appendix C of this part. Compliance must be
shown using the ice accretions defined in part II of appendix C of this
part, assuming normal operation of the airplane and its ice protection
system in accordance with the operating limitations and operating
procedures established by the applicant and provided in the Airplane
Flight Manual.
    (3) If the applicant does not seek certification for flight in all
icing conditions defined in appendix O of this part, each requirement
of this subpart, except Sec. Sec.  25.105, 25.107, 25.109, 25.111,
25.113, 25.115, 25.121, 25.123, 25.143(b)(1), (b)(2), and (c)(1),
25.149, 25.201(c)(2), 25.207(c) and (d), 25.239, and 25.251(b) through
(e), must be met in the appendix O icing conditions for which
certification is not sought in order to allow a safe exit from those
conditions. Compliance must be shown using the ice accretions defined
in part II, paragraphs (b) and (d) of appendix O of this part, assuming
normal operation of the airplane and its ice protection system in
accordance with the operating limitations and operating procedures
established by the applicant and provided in the Airplane Flight
Manual.
    (4) If the applicant seeks certification for flight in any portion
of the icing conditions of appendix O of this part, each requirement of
this subpart, except Sec. Sec.  25.123(c), 25.143(b)(1) and (2),
25.149, 25.201(c)(2), 25.207(c) and (d), 25.239, and 25.251(b) through
(e), must be met in the appendix O icing conditions for which
certification is sought. Compliance must be shown using the ice
accretions defined in part II, paragraphs (c) and (d) of appendix O of
this part, assuming normal operation of the airplane and its ice
protection system in accordance with the operating limitations and
operating procedures established by the applicant and provided in the
Airplane Flight Manual.
    3. Amend Sec.  25.105 by revising paragraph (a)(2) introductory
text to read as follows:

Sec.  25.105  Takeoff.

    (a) * * *
    (2) In icing conditions, if in the configuration used to show
compliance with Sec.  25.121(b), and with the most critical of the
takeoff ice accretion(s) defined in appendices C and O of this part, as
applicable, in accordance with Sec.  25.21(g):
* * * * *
    4. Amend Sec.  25.111 by revising paragraphs (c)(5)(i) and
(c)(5)(ii) to read as follows:

Sec.  25.111  Takeoff path.

* * * * *
    (c) * * *
    (5) * * *
    (i) With the most critical of the takeoff ice accretion(s) defined
in appendices C and O of this part, as applicable, in accordance with
Sec.  25.21(g), from a height of 35 feet above the takeoff surface up
to the point where the airplane is 400 feet above the takeoff surface;
and
    (ii) With the most critical of the final takeoff ice accretion(s)
defined in appendices C and O of this part, as applicable, in
accordance with Sec.  25.21(g), from the point where the airplane is
400 feet above the takeoff surface to the end of the takeoff path.
* * * * *
    5. Amend Sec.  25.119 by revising paragraph (b) to read as follows:

Sec.  25.119  Landing climb: All-engines-operating.

* * * * *
    (b) In icing conditions with the most critical of the landing ice
accretion(s) defined in appendices C and O of this part, as applicable,
in accordance with Sec.  25.21(g), and with a climb speed of
VREF determined in accordance with Sec.  25.125(b)(2)(ii).
    6. Amend Sec.  25.121 by revising paragraphs (b)(2)(ii)
introductory text, (c)(2)(ii) introductory text, and (d)(2)(ii) to read
as follows:

Sec.  25.121  Climb: One-engine-inoperative.

* * * * *
    (b) * * *
    (2) * * *
    (ii) In icing conditions with the most critical of the takeoff ice
accretion(s) defined in appendices C and O of this part, as applicable,
in accordance with Sec.  25.21(g), if in the configuration used to show
compliance with Sec.  25.121(b) with this takeoff ice accretion:
* * * * *
    (c) * * *
    (2) * * *
    (ii) In icing conditions with the most critical of the final
takeoff ice accretion(s) defined in appendices C and O of this part, as
applicable, in accordance with Sec.  25.21(g), if in the configuration
used to show compliance with Sec.  25.121(b) with the takeoff ice
accretion used to show compliance with Sec.  25.111(c)(5)(i):
* * * * *
    (d) * * *
    (2) * * *
    (ii) In icing conditions with the most critical of the approach ice
accretion(s) defined in appendices C and O of this part, as applicable,
in accordance with Sec.  25.21(g). The climb speed selected for non-
icing conditions may be used if the climb speed for icing conditions,
computed in accordance with paragraph (d)(1)(iii) of this section, does
not exceed that for non-icing conditions by more than the greater of 3
knots CAS or 3 percent.
    7. Amend Sec.  25.123 by revising paragraph (b)(2) introductory
text to read as follows:

Sec.  25.123  En-route flight paths.

* * * * *
    (b) * * *
    (2) In icing conditions with the most critical of the en route ice
accretion(s) defined in appendices C and O of this part, as applicable,
in accordance with Sec.  25.21(g), if:
* * * * *
    8. Amend Sec.  25.125 by revising paragraphs (a)(2), (b)(2)(ii)(B),
and (b)(2)(ii)(C) to read as follows:

Sec.  25.125  Landing.

    (a) * * *
    (2) In icing conditions with the most critical of the landing ice
accretion(s) defined in appendices C and O of this part, as applicable,
in accordance with Sec.  25.21(g), if VREF for icing
conditions exceeds VREF for non-icing conditions by more
than 5 knots CAS at the maximum landing weight.
    (b) * * *
    (2) * * *
    (ii) * * *
    (B) 1.23 VSR0 with the most critical of the landing ice
accretion(s) defined in appendices C and O of this part, as applicable,
in accordance with Sec.  25.21(g), if that speed exceeds
VREF selected for non-icing conditions by more than 5 knots
CAS; and
    (C) A speed that provides the maneuvering capability specified in
Sec.  25.143(h) with the most critical of the landing ice accretion(s)
defined in appendices C and O of this part, as applicable, in
accordance with Sec.  25.21(g).
* * * * *
    9. Amend Sec.  25.143 by revising paragraphs (c) introductory text,
(i)(1), and (j) introductory text to read as follows:

Sec.  25.143  Controllability and maneuverability--General.

* * * * *
    (c) The airplane must be shown to be safely controllable and
maneuverable with the most critical of the ice accretion(s) appropriate
to the phase of flight as defined in appendices C and O of this part,
as applicable, in accordance

with Sec.  25.21(g), and with the critical engine inoperative and its
propeller (if applicable) in the minimum drag position:
* * * * *
    (i) * * *
    (1) Controllability must be demonstrated with the most critical of
the ice accretion(s) for the particular flight phase as defined in
appendices C and O of this part, as applicable, in accordance with
Sec.  25.21(g);
* * * * *
    (j) For flight in icing conditions before the ice protection system
has been activated and is performing its intended function, it must be
demonstrated in flight with the most critical of the ice accretion(s)
defined in appendix C, part II, paragraph (e) of this part and appendix
O, part II, paragraph (d) of this part, as applicable, in accordance
with Sec.  25.21(g), that:
* * * * *
    10. Amend Sec.  25.207 by revising paragraphs (b), (e)(1) through
(5), and (h) introductory text to read as follows:

Sec.  25.207  Stall warning.

* * * * *
    (b) The warning must be furnished either through the inherent
aerodynamic qualities of the airplane or by a device that will give
clearly distinguishable indications under expected conditions of
flight. However, a visual stall warning device that requires the
attention of the crew within the cockpit is not acceptable by itself.
If a warning device is used, it must provide a warning in each of the
airplane configurations prescribed in paragraph (a) of this section at
the speed prescribed in paragraphs (c) and (d) of this section. Except
for the stall warning prescribed in paragraph (h)(3)(ii) of this
section, the stall warning for flight in icing conditions must be
provided by the same means as the stall warning for flight in non-icing
conditions.
* * * * *
    (e) * * *
    (1) The most critical of the takeoff ice and final takeoff ice
accretions defined in appendices C and O of this part, as applicable,
in accordance with Sec.  25.21(g), for each configuration used in the
takeoff phase of flight;
    (2) The most critical of the en route ice accretion(s) defined in
appendices C and O of this part, as applicable, in accordance with
Sec.  25.21(g), for the en route configuration;
    (3) The most critical of the holding ice accretion(s) defined in
appendices C and O of this part, as applicable, in accordance with
Sec.  25.21(g), for the holding configuration(s);
    (4) The most critical of the approach ice accretion(s) defined in
appendices C and O of this part, as applicable, in accordance with
Sec.  25.21(g), for the approach configuration(s); and
    (5) The most critical of the landing ice accretion(s) defined in
appendices C and O of this part, as applicable, in accordance with
Sec.  25.21(g), for the landing and go-around configuration(s).
* * * * *
    (h) The following stall warning margin is required for flight in
icing conditions before the ice protection system has been activated
and is performing its intended function. Compliance must be shown using
the most critical of the ice accretion(s) defined in appendix C, part
II, paragraph (e) of this part and appendix O, part II, paragraph (d)
of this part, as applicable, in accordance with Sec.  25.21(g). The
stall warning margin in straight and turning flight must be sufficient
to allow the pilot to prevent stalling without encountering any adverse
flight characteristics when:
* * * * *
    11. Amend Sec.  25.237 by revising paragraph (a)(3)(ii) to read as
follows:

Sec.  25.237  Wind velocities.

    (a) * * *
    (3) * * *
    (ii) Icing conditions with the most critical of the landing ice
accretion(s) defined in appendices C and O of this part, as applicable,
in accordance with Sec.  25.21(g).
* * * * *
    12. Amend Sec.  25.253 by revising paragraph (c) introductory text
to read as follows:

Sec.  25.253  High-speed characteristics.

* * * * *
    (c) Maximum speed for stability characteristics in icing
conditions. The maximum speed for stability characteristics with the
most critical of the ice accretions defined in appendices C and O of
this part, as applicable, in accordance with Sec.  25.21(g), at which
the requirements of Sec. Sec.  25.143(g), 25.147(e), 25.175(b)(1),
25.177 and 25.181 must be met, is the lower of:
* * * * *
    13. Amend Sec.  25.773 by revising paragraph (b)(1)(ii) to read as
follows:

Sec.  25.773  Pilot compartment view.

* * * * *
    (b) * * *
    (1) * * *
    (ii) The icing conditions specified in appendix C and the following
icing conditions specified in appendix O of this part, if certification
for flight in icing conditions is sought:
    (A) For airplanes certificated in accordance with Sec.
25.1420(a)(1), the icing conditions that the airplane is certified to
safely exit following detection.
    (B) For airplanes certificated in accordance with Sec.
25.1420(a)(2), the icing conditions that the airplane is certified to
safely operate in and the icing conditions that the airplane is
certified to safely exit following detection.
    (C) For airplanes certificated in accordance with Sec.
25.1420(a)(3) and for airplanes not subject to Sec.  25.1420, all icing
conditions.
* * * * *
    14. Amend Sec.  25.903 by adding paragraph (a)(3) to read as
follows:

Sec.  25.903  Engines.

    (a) * * *
    (3) Each turbine engine must comply with one of the following
paragraphs:
    (i) Section 33.68 of this chapter in effect on [effective date of
final rule], or as subsequently amended; or
    (ii) Section 33.68 of this chapter in effect on February 23, 1984,
or as subsequently amended before [effective date of final rule],
unless that engine's ice accumulation service history has resulted in
an unsafe condition; or
    (iii) Section 33.68 of this chapter in effect on October 1, 1974,
or as subsequently amended prior to February 23, 1984, unless that
engine's ice accumulation service history has resulted in an unsafe
condition; or
    (iv) Be shown to have an ice accumulation service history in
similar installation locations which has not resulted in any unsafe
conditions.
* * * * *
    15. Amend Sec.  25.929 by revising paragraph (a) to read as
follows:

Sec.  25.929  Propeller deicing.

    (a) If certification for flight in icing is sought there must be a
means to prevent or remove hazardous ice accumulations that could form
in the icing conditions defined in appendices C and O of this part on
propellers or on accessories where ice accumulation would jeopardize
engine performance.
* * * * *
    16. Amend Sec.  25.1093 by revising paragraph (b) to read as
follows:

Sec.  25.1093  Induction system icing protection.

* * * * *
    (b) Turbine engines. Each engine, with all icing protection systems
operating, must:
    (1) Operate throughout its flight power range, including the
minimum descent idling speeds, in the icing

conditions defined in appendices C and O of this part, and appendix D
of part 33 of this chapter, and in falling and blowing snow within the
limitations established for the airplane for such operation, without
the accumulation of ice on the engine, inlet system components or
airframe components that would do any of the following:
    (i) Adversely affect installed engine operation or cause a
sustained loss of power or thrust; or an unacceptable increase in gas
path operating temperature; or an airframe/engine incompatibility; or
    (ii) Result in unacceptable temporary power loss or engine damage;
or
    (iii) Cause a stall, surge, or flameout or loss of engine
controllability (for example, rollback).
    (2) Idle for a minimum of 30 minutes on the ground in the following
icing conditions shown in Table 1, unless replaced by similar test
conditions that are more critical. These conditions must be
demonstrated with the available air bleed for icing protection at its
critical condition, without adverse effect, followed by an acceleration
to takeoff power or thrust. During the idle operation the engine may be
run up periodically to a moderate power or thrust setting in a manner
acceptable to the Administrator. The applicant must document the engine
run-up procedure (including the maximum time interval between run-ups
from idle, run-up power setting, and duration at power) and associated
minimum ambient temperature demonstrated for the maximum time interval,
and these conditions must be used in establishing the airplane
operating limitations in accordance with Sec.  25.1521.

                                                       Table 1--Icing Conditions for Ground Tests
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                            Water concentration      Mean effective
             Condition              Total air temperature        (minimum)          particle diameter                     Demonstration
--------------------------------------------------------------------------------------------------------------------------------------------------------
(i) Rime ice condition............  0 to 15 [deg]F (-18    Liquid--0.3 g/m\3\...  15-25 microns.......  By test, analysis or combination of the two.
                                     to -9 [deg]C).
(ii) Glaze ice condition..........  20 to 30 [deg]F (-7    Liquid--0.3 g/m\3\...  15-25 microns.......  By test, analysis or combination of the two.
                                     to -1 [deg]C).
(iii) Large drop condition........  15 to 30 [deg]F (-9    Liquid--0.3 g/m\3\...  100 microns           By test, analysis or combination of the two.
                                     to -1 [deg]C).                                (minimum).
--------------------------------------------------------------------------------------------------------------------------------------------------------

* * * * *
    17. Amend Sec.  25.1323 by revising paragraph (i) to read as
follows:

Sec.  25.1323  Airspeed indicating system.

* * * * *
    (i) Each system must have a heated pitot tube or an equivalent
means of preventing malfunction in mixed phase and ice crystal
conditions as defined in Table 1 of this section, the icing conditions
defined in appendix C of this part, and the following icing conditions
specified in appendix O of this part:
    (1) For airplanes certificated in accordance with Sec.
25.1420(a)(1), the icing conditions that the airplane is certified to
safely exit following detection.
    (2) For airplanes certificated in accordance with Sec.
25.1420(a)(2), the icing conditions that the airplane is certified to
safely operate in and the icing conditions that the airplane is
certified to safely exit following detection.
    (3) For airplanes certificated in accordance with Sec.
25.1420(a)(3) and for airplanes not subject to Sec.  25.1420, all icing
conditions.

                                             Table 1--Icing Conditions for Airspeed Indicating System Tests

--------------------------------------------------------------------------------------------------------------------------------------------------------
Air temperature                               Altitude range               Ice water      Liquid     Horizontal extent    Ice median mass...      Liquid
                                                                             content       water                          dimension.........   water MVD
                                                                                content
--------------------------------------------------------------------------------------------------------------------------------------------------------
([deg]C)                          (ft)..............  (m)...............      g/m\3\      g/m\3\        (km)   (n miles)  ([mu]m)...........     ([mu]m)
--------------------------------------------------------------------------------------------------------------------------------------------------------
0 to -20........................  10,000 to 30,000..  3,000 to 9,000....           4           1           5           3  100 to 1,000......          20
                                                                                1           1         100          50
                                                                                0.5         0.5         500         300
-20 to -40......................  15,000 to 40,000..  4,500 to 12,000...           5           0           5           3
                                                                                2           0          20          10
                                                                                1           0         100          50
                                                                                0.5           0         500         300
--------------------------------------------------------------------------------------------------------------------------------------------------------

* * * * *
    18. Add Sec.  25.1324 to read as follows:

Sec.  25.1324  Angle of attack system.

    Each angle of attack system sensor must be heated or have an
equivalent means of preventing malfunction in the mixed phase and ice
crystal conditions as defined in Sec.  25.1323, the icing conditions
defined in appendix C of this part, and the following icing conditions
specified in appendix O of this part:
    (a) For airplanes certificated in accordance with Sec.
25.1420(a)(1), the icing conditions that the airplane is certified to
safely exit following detection.
    (b) For airplanes certificated in accordance with Sec.
25.1420(a)(2), the icing conditions that the airplane is certified to
safely operate in and the icing conditions that the airplane is
certified to safely exit following detection.
    (c) For airplanes certificated in accordance with Sec.
25.1420(a)(3) and for airplanes not subject to Sec.  25.1420, all icing
conditions.
    19. Amend Sec.  25.1325 by revising paragraph (b) to read as
follows:

Sec.  25.1325  Static pressure systems.

* * * * *
    (b) Each static port must be designed and located so that:
    (1) The static pressure system performance is least affected by
airflow variation, or by moisture or other foreign matter, and
    (2) The correlation between air pressure in the static pressure
system and true ambient atmospheric static pressure is not changed when
the

airplane is exposed to the icing conditions defined in appendix C of
this part, and the following icing conditions specified in appendix O
of this part:
    (i) For airplanes certificated in accordance with Sec.
25.1420(a)(1), the icing conditions that the airplane is certified to
safely exit following detection.
    (ii) For airplanes certificated in accordance with Sec.
25.1420(a)(2), the icing conditions that the airplane is certified to
safely operate in and the icing conditions that the airplane is
certified to safely exit following detection.
    (iii) For airplanes certificated in accordance with Sec.
25.1420(a)(3) and for airplanes not subject to Sec.  25.1420, all icing
conditions.
* * * * *
    20. Add Sec.  25.1420 to read as follows:

Sec.  25.1420  Supercooled large drop icing conditions.

    (a) If certification for flight in icing conditions is sought, in
addition to the requirements of Sec.  25.1419, an airplane with a
maximum takeoff weight less than 60,000 pounds or with reversible
flight controls must be capable of operating in accordance with
paragraphs (a)(1), (2), or (3), of this section.
    (1) Operating safely after encountering the icing conditions
defined in appendix O of this part:
    (i) There must be a means provided to detect that the airplane is
operating in appendix O icing conditions; and
    (ii) Following detection of appendix O icing conditions, the
airplane must be capable of operating safely while exiting all icing
conditions.
    (2) Operating safely in a portion of the icing conditions defined
in appendix O of this part as selected by the applicant.
    (i) There must be a means provided to detect that the airplane is
operating in conditions that exceed the selected portion of appendix O
icing conditions; and
    (ii) Following detection, the airplane must be capable of operating
safely while exiting all icing conditions.
    (3) Operating safely in the icing conditions defined in appendix O
of this part.
    (b) To establish that the airplane can operate safely as required
in paragraph (a) of this section, an analysis must be performed to
establish that the ice protection for the various components of the
airplane is adequate, taking into account the various airplane
operational configurations. To verify the analysis, one, or more as
found necessary, of the following methods must be used:
    (1) Laboratory dry air or simulated icing tests, or a combination
of both, of the components or models of the components.
    (2) Laboratory dry air or simulated icing tests, or a combination
of both, of models of the airplane.
    (3) Flight tests of the airplane or its components in simulated
icing conditions, measured as necessary to support the analysis.
    (4) Flight tests of the airplane with simulated ice shapes.
    (5) Flight tests of the airplane in natural icing conditions,
measured as necessary to support the analysis.
    (c) For an airplane certified in accordance with paragraph (a)(2)
or (a)(3) of this section, the requirements of Sec.  25.1419 (e), (f),
(g), and (h) must be met for the icing conditions defined in appendix O
of this part in which the airplane is certified to operate.
    21. Amend Sec.  25.1521 by redesignating paragraph (c)(3) as (c)(4)
and revising it, and by adding new paragraph (c)(3) to read as follows:

Sec.  25.1521  Powerplant limitations.

* * * * *
    (c) * * *
    (3) Maximum time interval between engine run-ups from idle, run-up
power setting, duration at power, and the associated minimum ambient
temperature demonstrated for the maximum time interval, for ground
operation in icing conditions, as defined in Sec.  25.1093(b)(2).
    (4) Any other parameter for which a limitation has been established
as part of the engine type certificate except that a limitation need
not be established for a parameter that cannot be exceeded during
normal operation due to the design of the installation or to another
established limitation.
* * * * *
    22. Amend Sec.  25.1533 by adding paragraph (c) to read as follows:

Sec.  25.1533  Additional operating limitations.

* * * * *
    (c) For airplanes certified in accordance with Sec.  25.1420(a)(1)
or (a)(2), an operating limitation must be established to require
exiting all icing conditions if icing conditions defined in appendix O
of this part are encountered for which the airplane has not been
certified to safely operate.
    23. Amend part 25 by adding Appendix O to part 25 to read as
follows:

Appendix O to Part 25--Supercooled Large Drop Icing Conditions

    Appendix O consists of two parts. Part I defines appendix O as a
description of supercooled large drop (SLD) icing conditions in
which the drop median volume diameter (MVD) is less than or greater
than 40 [micro]m, the maximum mean effective drop diameter (MED) of
appendix C continuous maximum (stratiform clouds) icing conditions.
For appendix O, SLD icing conditions consist of freezing drizzle and
freezing rain occurring in and/or below stratiform clouds. Part II
defines ice accretions used to show compliance with part 25, subpart
B, airplane performance and handling qualities requirements.

Part I--Meteorology

    Appendix O icing conditions are defined by the parameters of
altitude, vertical and horizontal extent, temperature, liquid water
content, and water mass distribution as a function of drop diameter
distribution.
    (a) Freezing Drizzle (Conditions with spectra maximum drop
diameters from 100 [micro]m to 500 [micro]m):
    (1) Pressure altitude range: 0 to 22,000 feet MSL.
    (2) Maximum vertical extent: 12,000 feet.
    (3) Horizontal extent: standard distance of 17.4 nautical miles.
    (4) Total liquid water content.

    Note: Liquid water content (LWC) in grams per cubic meter (g/
m\3\) based on horizontal extent standard distance of 17.4 nautical
miles.

BILLING CODE 4910-13-P

[GRAPHIC] [TIFF OMITTED] TP29JN10.051

    (5) Drop diameter distribution:

[GRAPHIC] [TIFF OMITTED] TP29JN10.052

    (6) Altitude and temperature envelope:

[GRAPHIC] [TIFF OMITTED] TP29JN10.053

    (b) Freezing Rain (Conditions with spectra maximum drop
diameters greater than 500 [micro]m):
    (1) Pressure altitude range: 0 to 12,000 ft MSL.
    (2) Maximum vertical extent: 7,000 ft.
    (3) Horizontal extent: standard distance of 17.4 nautical miles.
    (4) Total liquid water content.

    Note:  LWC in grams per cubic meter (g/m\3\) based on horizontal
extent standard distance of 17.4 nautical miles.

[GRAPHIC] [TIFF OMITTED] TP29JN10.054

    (5) Drop Diameter Distribution

[GRAPHIC] [TIFF OMITTED] TP29JN10.055

    (6) Altitude and temperature envelope:

[GRAPHIC] [TIFF OMITTED] TP29JN10.056

    (c) Horizontal extent.
    The liquid water content for freezing drizzle and freezing rain
conditions for horizontal extents other than the standard 17.4
nautical miles can be determined by the value of the liquid water
content determined from Figure 1 or Figure 4, multiplied by the
factor provided in Figure 7.

[GRAPHIC] [TIFF OMITTED] TP29JN10.057

Part II--Airframe Ice Accretions for Showing Compliance With Subpart B

    (a) General.
    The most critical ice accretion in terms of airplane performance
and handling qualities for each flight phase must be used to show
compliance with the applicable airplane performance and handling
qualities requirements for icing conditions contained in subpart B
of this part. Applicants must demonstrate that the full range of
atmospheric icing conditions specified in part I of this appendix
have been considered, including drop diameter distributions, liquid
water content, and temperature appropriate to the flight conditions
(for example, configuration, speed, angle-of-attack, and altitude).
    (1) For an airplane certified in accordance with Sec.
25.1420(a)(1), the ice accretions for each flight phase are defined
in part II, paragraph (b) of this appendix.
    (2) For an airplane certified in accordance with Sec.
25.1420(a)(2), the most critical ice accretion for each flight phase
defined in part II, paragraphs (b) and (c) of this appendix, must be
used. For the ice accretions defined in part II, paragraph (c) of
this appendix, only the portion of part I of this appendix in which
the airplane is capable of operating safely must be considered.
    (3) For an airplane certified in accordance with Sec.
25.1420(a)(3), the ice accretions for each flight phase are defined
in part II, paragraph (c) of this appendix.
    (b) Ice accretions for airplanes certified in accordance with
Sec.  25.1420(a)(1) or (a)(2).
    (1) En route ice is the en route ice as defined by part II,
paragraph (c)(3), of this appendix, for an airplane certified in
accordance with Sec.  25.1420(a)(2), or defined by part II,
paragraph (a)(3), of appendix C of this part, for an airplane
certified in accordance with Sec.  25.1420(a)(1), plus:
    (i) Pre-detection ice as defined by part II paragraph (b)(5) of
this appendix; and
    (ii) The ice accumulated during the transit of one cloud with a
horizontal extent of 17.4 nautical miles in the most critical of the
icing conditions defined in part I of this appendix and one cloud
with a horizontal extent of 17.4 nautical miles in the continuous
maximum icing conditions defined in appendix C of this part.
    (2) Holding ice is the holding ice defined by part II, paragraph
(c)(4), of this appendix, for an airplane certified in accordance
with Sec.  25.1420(a)(2), or defined by part II, paragraph (a)(4) of
appendix C of this part, for an airplane certified in accordance
with Sec.  25.1420(a)(1), plus:
    (i) Pre-detection ice as defined by part II, paragraph (b)(5) of
this appendix; and
    (ii) The ice accumulated during the transit of one cloud with a
17.4 nautical miles horizontal extent in the most critical of the
icing conditions defined in part I of this appendix and one cloud
with a horizontal extent of 17.4 nautical miles in the continuous
maximum icing conditions defined in appendix C of this part. The
total exposure to the icing conditions need not exceed 45 minutes.
    (3) Approach ice is the more critical of the holding ice defined
by part II, paragraph (b)(2) of this appendix, or the ice calculated
in the applicable paragraph (b)(3)(i) or (ii) of part II of this
appendix:
    (i) For an airplane certified in accordance with Sec.
25.1420(a)(2), the ice accumulated during descent from the maximum
vertical extent of the icing conditions defined in part I of this
appendix to 2,000 feet above the landing surface in the cruise
configuration, plus transition to the approach configuration, plus:
    (A) Pre-detection ice, as defined by part II, paragraph (b)(5)
of this appendix; and