ASRS Directline

 Issue Number 4 : June 1993

The Sterile Cockpit

by Robert L. Sumwalt

It's no secret. When a flight crew's attention is diverted from the task of flying, the chance of error increases. Over the years there have been dozens of air carrier accidents that occurred when the crew diverted attention from the task at hand and became occupied with items totally unrelated to flying. Consequently, important things were missed. Things like setting the flaps prior to takeoff, or extending the landing gear before landing. Things like monitoring altitude on an instrument approach, or using engine anti-ice for takeoff during a blinding snow storm.

In 1981 the FAA enacted FAR 121.542 and FAR 135.100 to help curb the number of these accidents. Commonly known as the "sterile cockpit rule," these regulations specifically prohibit crew member performance of non-essential duties or activities while the aircraft is involved in taxi, takeoff, landing, and all other flight operations conducted below 10,000 feet MSL, except cruise flight. (Click here to go to FAR 121.542 and 135.100 .)

It's unrealistic to expect a crew to fly together for several days and never discuss anything except items related to flying the aircraft. In fact, experts have demonstrated that in order to be most effective, crews need to talk -- even if it is just merely "get to know you" sort of chat. The sterile cockpit rule is a good rule because it clearly defines when it is time to set aside non-essential activities and tend strictly to the task at hand -- that of safely operating the aircraft.

In spite of the existence of the sterile cockpit rule over the past decade, pilots have continued to have accidents and serious incidents that perhaps could have been prevented. For the most part, disobeying the rule is not intentional. It just happens. But as this review shows, the consequences of non-compliance can be very serious. Truly, the sterile cockpit needs to be cleaned up.

This reviewer used the ASRS database to find specific examples of problems related to non-compliance with the sterile cockpit rule. We carefully reviewed 63 reports that had been previously coded by analysts as having some relevance to the sterile cockpit rule. Here is a synopsis of the problems that we found that could be attributed to sterile cockpit violations:

48% were altitude deviations

14% were course deviations

14% were runway transgressions

14% were general distractions with no specific adverse consequences

8% involved takeoffs or landings without clearance

2% involved near mid-air collisions due to inattention and distractions.

The Culprits

The way in which the sterile cockpit rule was broken in each report was tallied and analyzed. Some reports contained more than one culprit. Many of the reports contained acknowledgments like this:

Following are the four most common reasons for non-adherence to the sterile cockpit rule:

Extraneous Conversation

The most habitually cited offense was extraneous conversation between cockpit crew members. Cited one First Officer:

The Captain of an air carrier aircraft admits to conversation not pertinent to flying duties:

Five reports detailed extraneous conversation with jump seat riders. The ability to ride on an air carrier's jump seat is quite a valuable privilege, but it is important that the additional cockpit rider not be allowed to create distractions. A look at two of these reports:

And in the other ASRS submission:

The connotation "extraneous conversation" does not always have to imply just those persons on board the aircraft. Look at how extraneous chatter with air traffic controllers introduced problems for these crews. Air traffic controllers, take notice:

And in another incident:

Distractions from Flight Attendants

Distractions caused by flight attendants visiting the cockpit or calling on the interphone were noted in almost one quarter of the reports in our data set. This was our second highest source of deviation from the sterile cockpit rule.

In another incident, the crew was surprised when they lined up with the wrong runway -- and doubly surprised when they noticed they were in an unplanned formation with a jet landing on the same runway!

Non-Pertinent Radio Calls and PA Announcements

Several reports we examined indicate that problems arose when non-pertinent company radio calls and PA announcements were made below 10,000 feet. Remember, below 10,000 feet if it's not directly related to flight safety, it's in violation with the sterile cockpit rule.

While being vectored in a busy terminal area, the Captain in the following report called on the company radio frequency to notify maintenance about a minor cabin discrepancy. As the reporter soon discovered, his absence from the ATC frequency caused an overload with his First Officer. Several ATC radio calls were missed. The controller growled a little, they lost their landing sequence, and the pilot's pride was hurt. But a valuable lesson was also learned.


Nowhere does Webster's define "sight-seeing" as an activity that is essential to the safe operation of aircraft. When sight-seeing is conducted by flight crew members below 10,000 feet, not only is it potentially dangerous, but it is illegal, as well. Two reports demonstrated that a cockpit full of sight-seeing crew members is an ASRS report looking for a place to happen -- possibly even an accident.

In another incident report:

Recommendations and Considerations

The sterile cockpit rule was designed to help minimize many of the problems that we just annotated. Judging from these reports, a safer operation can be achieved by simply abiding by the rule's guidelines.

In the Beginning

A good time to establish the desire to maintain a sterile cockpit environment is before beginning a trip. In briefing cockpit and cabin crew members the captain can politely say, "I think the sterile cockpit rule is really important, so we'll adhere to it. Okay?"

Setting the Standards

During the preflight briefing the captain should also inform the flight attendants how they can determine if the flight is above or below 10,000 feet. Many companies have already established procedures for this, such as a "10,000 foot PA announcement," or a call to the flight attendants on the interphone. However, these procedures require one crew member to be "out of the loop." And as evidenced by literally thousands of ASRS reports, the potential for problems (such as misunderstood clearances and altitude deviations) increases when a crew member is out of the loop. Some airlines have installed a cockpit-controlled "sterile cockpit light" that can be illuminated when descending below 10,000 feet and extinguished when climbing above 10,000 feet. For those who develop company procedures, consideration should be given to developing something that doesn't create its own set of distractions. With the increased use of two-crew member cockpits this consideration is increasingly important.

Unexpected Entry

Unexpected calls or cockpit entry by flight attendants during the sterile cockpit period can be distracting and potentially dangerous. It is recommended that the Captain, during the pre-departure crew briefing, emphasize the importance of the sterile cockpit rule and request that flight attendant calls or entry during this time be undertaken only for reasons of great urgency. As one reporter resolves:

High Altitude Airports

Another reporter offered a good suggestion involving high elevation airports, where 10,000 feet MSL for the sterile cockpit boundary may be too low.

Low Altitude Flight

This reporter, a commuter pilot who often has cruise altitudes below 10,000 feet MSL, offers a similar worthwhile suggestion following an altitude deviation.

"I believe this situation occurred because our cruise altitude was 8000 feet, and we were accustomed to conversation and other activities along the route and were not observing the 'sterile cockpit' environment. Would suggest that, in these flight circumstances where cruise altitude is less than 10,000 feet, crews make a specific DME mileage their beginning for 'total concentration-sterile cockpit' procedures." (ACN 173707)

No person about to undergo major surgery would think too kindly of the surgical team who failed to sterilize themselves and their operating instruments before the operation. After a series of air carrier accidents and serious incidents, the traveling public feels the same way about their crew members. Keep the sterile cockpit "clean." Your fellow crew members and passengers are hoping that you will.

 Cockpit Chatter Leads to Crash

From Flight Safety Foundation's August 1992 Flight Safety Digest
(Accident/Incident Briefs)

DHC Dash 7. Aircraft Destroyed. Thirty-six fatalities.

The four-engine Dash 7 was on an instrument approach to Runway 04 when it crashed into high terrain about five nautical miles from the airport. At the time of the crash, the aircraft was slightly off course and flying at an altitude of 560 feet MSL (mean sea level). The published minimum altitude at the area of impact was 1,200 feet MSL.

A subsequent investigation indicated that the pilot was having a conversation with a passenger who was sitting on the jump seat. The report said the crew was likely distracted by the conversation. The report cited the pilot and co-pilot for poor airmanship in not monitoring altitude and course information.

Sterile Cockpit Rules

FAR 121.542 / FAR 135.100--Flight Crew Member Duties

(a) No certificate holder shall require, nor may any flight crew member perform any duties during a critical phase of flight except those duties required for the safe operation of the aircraft. Duties such as company required calls made for non-safety related purposes as ordering galley supplies and confirming passenger connections, announcements made to passengers promoting the air carrier or pointing out sights of interest and filling out company payroll and related records are not required for the safe operation of the aircraft.

(b) No flight crew member may engage in, nor may any pilot in command permit, any activity during a critical phase of flight which could distract any flight crew member from the performance of his or her duties or which could interfere in any way with the proper conduct of those duties. Activities such as eating meals, engaging in non-essential conversations within the cockpit and non-essential communications between the cabin and cockpit crews, and reading publications not related to the proper conduct of the flight are not required for the safe operation of the aircraft.

(c) For the purposes of this section, critical phase of flight involves all ground operations involving taxi, takeoff and landing, and all other flight operations conducted below 10,000 feet, except cruise flight.

Note: Taxi is defined as "movement of an airplane under its own power on the surface of an airport."

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