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.
