Inadequate Preflight

The NTSB often cites hasty or neglected preflight inspections as an accident cause, but is there more to the story?

In the past 10 years, the National Transportation Safety Board has used the phrase "inadequate preflight inspection" in the probable causes of 15 fatal accidents. The most common direct cause is fuel contamination, usually with water, which typically leads to power loss after takeoff and a subsequent stall-spin. Other oversights include improperly latched baggage doors; various kinds of protective gear left in place, like pitot covers, control locks and foam air-intake plugs; oil filler or fuel tank caps unsecured; or failure to remove a boarding ladder or a chock. (A chock may seem unlikely to cause a fatal accident, but a passenger disembarked and was struck by an idling propeller while removing one from in front of a nosewheel.) Noteworthy about these causes is the fact that most of them-most especially unlatched baggage doors-should not have prevented the airplane from landing safely; but some pilots, rattled by the unfamiliar, lose control of perfectly flyable airplanes while returning to land.

Also noteworthy among the discrepancies listed here is the fact that any reasonably attentive preflight inspection would have detected them. The only instance, among the 15 accidents, of an anomaly that a normal preflight would not have detected was in the case of a long-stored airplane whose fuel tank vents had been clogged up by mud-daubing wasps; but that particular airplane had so many other things wrong with it, including a missing spark plug, that if the wasps hadn't gotten it something else would.

Accidents attributed to careless preflight inspections may leave pilots unmoved, because they feel that they would not have made the same mistake. More sobering are accidents in which the NTSB does not cite inadequate preflight among the causes, but that could have been prevented by a more than usually assiduous preflight inspection.

In April, 2001, a Schleicher ASW-20 sailplane shot up on takeoff into an uncontrolled 45-degree climb. The tow plane, to keep its tail from being lifted to a dangerous angle, jettisoned the tow rope. The sailplane leveled out briefly. The pilot then lowered the flaps, whereupon the ship pitched over into a dive and struck the ground. The pilot was killed.

On inspection of the wreckage it was immediately evident that the elevator pushrod had not been attached to the elevator. The pilot, who had flown the glider at least 50 times and had assembled it himself as many as 25 times, had taken his time assembling it about two hours before the flight. As he was awaiting tow, a friend of his (who was also a former co-owner of the glider) had helped him to check control continuity. The check they used for the elevator was for the pilot to apply up-elevator stick while the friend held the elevator. In retrospect, after the accident, the friend realized that in this test the rod could push against the elevator from below without actually being attached to it. It would only be by a down-elevator control input, which would pull the control pushrod away from the elevator, that continuity could be positively verified. The instruction manual for the sailplane specified a pulling motion to verify the proper attachment of the control rods to the ailerons and airbrakes, but did not mention this method with regard to the elevator. It stated that a "positive control check" should be performed before each flight, but did not say, in the case of the elevator, what such a check ought to consist of.

The NTSB report does not comment on the fact that a disconnected elevator does not make an ASW-20, or for that matter any other airplane, unflyable. The situation is aerodynamically no different from what occurs when the pilot removes his hand from the stick. The ASW-20's spring trim system would be useless, since it operates through the same pushrod as the stick control does, but the flaps can be used to trim the airplane to some extent. Their effect varies, however, depending on the rigging and ballasting of different aircraft. It seems that after leveling out the pilot was trying to use flaps, possibly for longitudinal control, but that the airplane got away from him.

Another accident, which happened to take place within two weeks of the glider crash, also involved a pitch control gone awry. The airplane was a Cessna 402B in Part 135 cargo service. It had flown 10 hours since having its right elevator replaced. On arriving at his destination airport, the pilot reported that he was going to circle a few times before landing because he was "having trouble with his autopilot." After circling, the 402 was on final approach at a height of about 200 feet when suddenly it nosed over and struck the ground in a 25-degree dive. The pilot, whose transmissions preceding the abrupt loss of control were "calm and completely un-alarmed," died in the accident.

Investigators examining the wreckage noted that the position of the pitch trim tab, which is located on the right elevator, seemed unusual. They measured it at 28 degrees tab-up, or aircraft nose down. Normally, tab-up travel is limited to five degrees. Cutting open the elevator, they found the front end of the tab's actuating pushrod jammed against the elevator's front spar. There was no evidence of damage to either the rod clevis or to the actuator screw to which it should have been attached, indicating that the attachment bolt had not been installed or, if it had, that it had slid out and disappeared.

Like many NTSB field reports, compiled by local FAA personnel, this one raises more questions than it answers. If no bolt had been installed during the replacement of the right elevator, it hardly seems likely that the 402 could have flown 10 hours without someone noticing that the airplane had no pitch trim. One has to suspect that a bolt was installed, but subsequently fell out; and in that case one also suspects that an extremely punctilious preflight inspection might have revealed a missing cotter pin or a loose nut in the process of backing out.

But this is the kind of preflight inspection that few pilots perform. Why? There can be many reasons. Airplanes that are in frequent use are assumed to be in working order; the fact that they have recently flown seems in and of itself to prove their readiness to fly again. Furthermore, control-system continuity is so fundamental that pilots take it for granted, assuming that periodic professional inspections are all that is required. Besides, most of the control system is hidden from view anyway; why should the few connections that happen to be visible deserve close inspection, when we are content to leave all the others hidden? Finally, many pilots don't know what an assembly like, for instance, the connection of a clevis-ended pushrod and a blade-ended jackscrew ought to look like, and might not observe the absence of a locking pin or notice a telltale gap between a nut or a bolt head and the surface against which it ought to be pulled up snugly.

Even conscientious pilots can overlook items during a preflight examination. But the fact that a certain number of fatalities-and, therefore, one assumes, a much greater number of disagreeable but nonfatal events-have come about as a result of faulty preflights should motivate us to approach the preflight not as a tedious duty to be disposed of as perfunctorily as possible, but rather as a serious task deserving our full attention.

Given, however, that people are going to make mistakes and that discrepancies that were in principle detectable on preflight are going to be overlooked from time to time, it is worth stopping to reflect on two facts. One is that the majority of preflighting mistakes still involve fuel. It does not take a lot of mechanical aptitude to drain sumps; why don't people do it? Because it's pouring rain, or dark? All the more reason.

The other is that airplanes can be flown with baggage doors open, pitot covers in place and boarding ladders dangling from their sides. The accidents that these problems cause are the results not of the problems themselves, but of too-tight turns at low altitude, failure to maintain airspeed, and other basic errors of ship-handling into which startled, excited pilots seem to fall in their haste to get back on the ground. All too often, the difference between a minor mischance and a major accident boils down to nothing more than elementary flying technique.

This article is based solely on the National Transportation Safety Board's report of the accidents and is intended to bring the issues raised to the attention of our readers. It is not intended to judge or to reach any definitive conclusions about the ability or capacity of any person, living or dead, or any aircraft or accessory.