October 2003Departments

Accident Analysis

Propeller hazards

One way to make a quick appraisal of a pilot's safety consciousness before ever leaving the ground is to watch how he behaves in the vicinity of the propeller. Does he use it as a leaning post while posing for a photograph or when chatting up the line crew during fueling? Does he horse the airplane around by the prop hub rather than dig the towbar out of the baggage compartment? Does he really look at the prop during preflight, and know what he's looking for? Does he board passengers before starting the engine-even if that means taxiing to the terminal from a distant hangar and shutting down again to load up and conduct a safety briefing? Does he shoo awestruck passengers away from the danger zone when they attempt to make physical contact with the prop as part of the ritual of getting acquainted with the airplane, as so many seem to need to do?

During engine start, does he carefully survey the surrounding area for people, pets, and property before turning the key or pressing the starter button-or does he simply croak "Clear" out the side window and then jump on the starter? What does "Clear" mean, anyway? All clear? Clear out? Are "Prop clear!" and "Clear prop!"-the two most popular variations-any better? Does the innocent bystander milling about near the aircraft have any idea what you are talking about? What pilot has not seen a bystander stare blankly, rooted to the spot, after hearing such a warning? But here's some history. The old Cessna 120-140 manual says to shout "Clear!" before starting and then wait for an answering shout of "Clear!" from "ground crew personnel"-so apparently this ritual is something held over from the old days.

This reminds one of the enigmatic cry of "Fore!" offered by golfers before they tee off. Does anyone but a golfer know why they say that? According to one dictionary, the utterance is "used by a golfer to warn anyone within range of the probable line of flight of his ball." In some cases this could take in a rather wide azimuth. Wider, presumably, than some bystanders might suspect, even if they know what "Fore" means.

Might one be so bold as to suggest calling out, "Starting engine, stand clear" as an alternative before starting an airplane? A bit wordy, but it gets the point across. Golfers will probably resist surrendering "Fore" to a clearer warning, in deference to tradition; let them. There are fewer nongolfers standing in front of the tee than there are nonpilots in the vicinity of parked aircraft about to be started, or aircraft idling on the ramp before taxi. And as far as the possible hazards, well, there's no comparison there either. A fatal accident in Fresno, California, occurring when a passenger walked into the turning propeller of a Cessna 182, will illustrate the point.

The accident occurred on October 29, 1998. According to the report by the National Transportation Safety Board, "The pilot stated that he was waiting in the transient tie-down parking ramp near the terminal for his passengers to arrive. They contacted him by cell phone and told him they were in the terminal parking lot and would be there shortly and to start the engine. The pilot said he then got into the airplane, started the engine, turned on the strobes and navigation lights, and then waited for the passengers to come."

The pilot waited a few minutes for the passengers to arrive. Then the tragedy struck. "After looking at the instruments he looked up and saw one of the intended passengers in front of the wing tip walking toward the engine. The passenger walked into the rotating propeller just as the pilot attempted to shut down the engine." The NTSB determined the accident cause as "the pilot's decision to allow unescorted passengers to approach the aircraft with the engine running, and the passenger's failure to see and avoid the rotating propeller. A factor in the accident was the low ambient lighting conditions, which would have made the rotating propeller difficult to see."

What about those times when one intentionally goes face to face with the prop to get a recalcitrant engine running? This subject is nearly taboo in polite discussions of aviation training, and absent from most pilot's operating handbooks. And with good reason: The dangers are many, and a hand-propping accident that occurred in Ashland, Virginia, serves as an excellent object lesson. Another problem is that the potential victim of such accidents is a second party pressed into service to get the aircraft going.

Even the hired help are extremely wary of hand-propping. "Finding a line person willing to prop an engine is like finding free avgas. They either don't know how or the FBO for whom they work prohibits hand-propping because of insurance restrictions," commented Barry Schiff in his "Proficient Pilot" column in the August 2002 AOPA Pilot, also noting that if the aircraft battery is truly dead, even hand starting will not get the avionics going again. That's not to say that hand-propping is never safe; obviously many older airplanes without starters and electrical systems had to be brought to life that way. Pilots who learned to fly in those days knew how their engines would behave during hand starts and positioned themselves accordingly (sometimes in front of the prop; sometimes behind it). They knew never to wrap their fingers completely around the blade, and they made absolutely certain of throttle position before beginning the procedure. Low-compression engines were easy to turn; high-compression powerplants or radials sitting up high on taildraggers were a different proposition. They knew what they were about and found helpers who would not make mistakes. But even these pilots' tales are larded with memories of lapses and mishaps.

The FAA's venerable Flight Training Handbook also abounds in caution on this subject, observing that all pilots "should be familiar with the procedures and dangers involved in starting an engine by turning the propeller by hand. Due to the associated hazards, this method of starting should be used only when absolutely necessary and when proper precautions have been taken."

The October 18, 2001, accident in Ashland, Virginia, as recounted by the NTSB, illustrates the concerns. After several attempts to start the Cessna 172 by other means, the pilot suggested hand-propping, and the line technician agreed. But here the accounts of the two parties diverged:

"From the pilot's perspective, when the technician attempted the start, he appeared to wrap both hands around the propeller, then pulled it downward using his full body weight. The engine started, and the technician appeared to lose his balance and fell into the propeller arc. The propeller clipped him in the back, picked up speed, struck him in the right forearm, and tore through his right leg."

The lineman's report had a different flavor. "According to the technician, the engine started running as soon as he touched the propeller. The technician didn't slip, but he 'wasn't quite ready for the propeller to turn over.' The technician also stated that he had been extremely careful during the start attempt, and if he hadn't been, the propeller 'would've taken my head off.'" The cause of the accident, as recorded in the AOPA Air Safety Foundation's accident database, was declared by the NTSB to have been "the line technician's inadvertent contact with the propeller during a hand-propped engine start."

Like other aviation accidents, propeller mishaps require a chain of events to come to fruition. A turning propeller, an unaware passenger, and perhaps bad lighting may have set the stage in one case. The decision to hand-prop, followed by an unexpectedly quick start, led to injury in the other. In another unlikely set of links in an accident chain, a Cessna 182 collided with parked cars in Frederick, Maryland, on August 1, 1990, when a pilot battling a failing starter disembarked and left a passenger remaining on board while he attempted to turn the propeller through a compression stroke. The ignition key was removed; he believed the switch was off, the throttle at idle, and the mixture in cutoff. The engine started, and the passenger said she panicked and may have advanced the throttle. But investigation also revealed that the ignition key could be removed "with the mag switch in any position." The NTSB determined that the switch was not "off" when the engine started.

A pilot's understanding of the elements of propeller safety may or may not be a highlight of a practical test. For example, on the Private Pilot-Airplane Practical Test, the engine-starting task merely lists among its objectives that the applicant exhibit knowledge of "hand-propping safety." (See the AOPA Air Safety Foundation's Propeller Safety Safety Advisor for a complete discussion.) The practical test also scrutinizes the applicant's regard for "the safety of nearby persons and property" which, of course, includes propeller clearance and judgment as to when it is safe to start the engine.

The reality is that safety and convenience sometimes conflict. When it does, pilots may have to sacrifice their own ease to protect other people on the airport; whether from their innocence about airplanes and propellers, or from their desire to be Good Samaritans and help get a disabled airplane moving again.

Dan Namowitz is an aviation writer and flight instructor. A pilot for 18 years and an instructor for 12, he enjoys learning to fly "anything new and different."