August 2002Departments

Accident Analysis

Preflight Oversights


Trust, But Verify

Sometimes the only surprising thing about an aircraft accident is how unsurprising the cause really was. From year to year, certain aviation-safety statistics remain remarkably predictable. Pilot-related accident causes - everything from inadequate preflight inspections to buzzing and flight into weather beyond the pilot's capability-tend to cause about 75 percent of all general aviation accidents, according to the AOPA Air Safety Foundation's 2001 Nall Report on general aviation accident trends and factors. Takeoff/climb accidents with pilot-related causes also held steady from 1999 to 2000, with only a 0.4 percent change in the likelihood of such events. "This should come as no surprise," notes the report. "In every form of human activity involving machinery, such as automobiles, boats, and aircraft, the hardware is invariably more reliable than the human operator simply because a bad design can be improved to 'engineer out' the problem."

Unfortunately, once a good design has been achieved, it can be modified to "engineer in" a new problem by a well-intentioned or unthinking user of the equipment. Take the control-wheel lock on a Cessna 152 or 172: Its design contains a fail-safe feature such that when it is installed in the airplane's control column, an appendage on the end of the device makes it difficult or impossible to insert an ignition key into the ignition switch. But many pilots miss the logic of this design and intentionally install the control lock backwards so that the ignition switch remains exposed. Anyone who has ever rented airplanes with any frequency has probably found one waiting in such a condition. Another case of negative reverse-engineering sometimes occurs when a control-wheel lock is lost and is replaced with an unsatisfactory substitute, such as a nail stuck in the control column. More than one wrecked airplane has been found with this kind of homemade control-column lock still in place.

Not that the "human operator" mentioned in the Nall Report is entirely beyond improvement. That's where training and habit-pattern development come in. Verifying that the flight controls are "free and correct" before takeoff should discover the nail in the column. The procedure should also avert accidents caused by inadvertent cross-rigging of controls during maintenance, but these accidents too still occur from time to time. One preventive exercise is the "thumb up, aileron up" check: With one hand on each horn of the control yoke, deflect the ailerons for a left turn-that is, left aileron up, right aileron down. As you move the yoke, your right thumb will be above your left thumb (see "Flying Smart: What It Looks Like," December 2001 AOPA Flight Training). It will also be pointing at the left, or "up," aileron.

Everyone commits human-factor blunders at some point in training, and the experience helps to ensure that it won't happen twice. Many a student pilot has completed the preflight inspection, climbed aboard, and fired up the engine - only to realize that the wings were still tied down. Often this discovery is made immediately before throttle was to be added to taxi away from the ramp, pointed out by a flight instructor who had already urged the trainee to take "just one more look around" to see if anything else needed to be done. There may have been a good reason to deviate from the checklist and not untie the wings earlier - a windy day, perhaps - but still, a problem was "engineered in" by a distraction or an unexpected change in priorities. Requiring the student to shut down the engine, get out, and untie the wings seems tyrannical and petty but is actually a valuable reinforcement technique, and it is a rare trainee who won't get the message.

Unfastened fuel-tank caps and oil dipsticks, or unremoved engine-cowl or pitot-tube coverings, have often been the cause of early engine shutdowns and restarts, or mishaps. (The pitot-tube covers, at least, usually come to the attention of unwary pilots when the "Remove Before Flight" ribbon attached to them begins to flap in the breeze during taxi.) You might consider these things the aerial equivalent of the automobile sitting next to you at a red light during the morning commute, with the owner's briefcase or a cup of coffee perched on its roof. But in an airplane these things have potentially much more serious repercussions, and the comic relief provided at the traffic light is missing.

On July 22, 2001, a Beechcraft Bonanza taxied out to depart Biddeford, Maine, for the Westchester County Airport in White Plains, New York. The airplane started down the runway but was unable to rotate for takeoff, running off the end of the runway and striking trees. "In a written statement, the pilot said he performed an engine run-up prior to takeoff without utilizing the airplane's checklist as he normally would. He then taxied to Runway 24, a 3,011-foot-long asphalt runway, for takeoff. During the takeoff roll, everything appeared normal; however, after obtaining rotation speed, he was not able to pull back on the control column. The airplane continued down the runway, until it departed the end of the runway and impacted several small trees. Post-accident examination of the airplane by a Federal Aviation Administration inspector revealed that the control column lock was installed in the control column," said the National Transportation Safety Board report on the accident.

The report minced no words in assigning as the cause of the mishap "the pilot's inadequate preflight inspection, which resulted in an attempted takeoff with a control column lock installed." The pilot, who had 1,300 hours of pilot time, including about 200 in the accident make and model, held commercial pilot and flight instructor certificates. The mishap resulted in an undisclosed certificate action against the pilot, according to a spokesman for the FAA's Portland, Maine, Flight Standards District Office.

Still, this pilot fared better than did a Beechcraft F35 pilot who had departed the previous day from Bamberg, South Carolina, in an airplane that had just undergone a top overhaul and annual inspection. The pilot lost control and crashed during the takeoff/climb phase while trying to cope with a sputtering engine. The preliminary accident report did not assign a cause, but it did note two important facts:

  • the airplane, which had been approved for use of auto fuel, had sat for nine days in one place since the last time the engine had been run, and
  • "according to personnel at the airport the pilot paid his bill, and within a short period of time, about two minutes, he started the airplane, taxied to Runway 5, and took off."

How long do a thorough preflight inspection and engine runup take? More than two minutes - even for an airplane far simpler than a Beech F35.

Another operator, the holder of a commercial pilot certificate, brought on unnecessary difficulties in July 2001 not by failing to perform preflight duties, but by delegating them to another party and then failing to verify that they had been correctly accomplished. In this case, it was insufficient fueling of a Cessna 150 that may have caused the airplane to come down in a vineyard near Delano, California, on July 2. "According to the pilot, his passenger fueled the airplane prior to departure. The passenger assured the pilot that the fuel tanks were completely full. The accident occurred three hours and 34 minutes after departure," said the preliminary NTSB report.

Had this accident occurred in 2000, it would have been one of 133 fuel-mismanagement accidents that happened during the year - and probably one of the most avoidable. "Knowledge of aircraft performance, realistic preflight fuel planning, and diligent monitoring of fuel consumption would prevent nearly all fuel exhaustion accidents," noted the Nall Report. How to further reduce that number by engineering the gambler's instinct out of the human operator remains the challenge of all flight training, and the task of all pilots each time they taxi out for takeoff.

Download a copy of the AOPA Air Safety Foundation's 2001 Nall Report from AOPA Online ( www.aopa.org/asf/publications/01nall.pdf ).

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


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