Often, experience leads us to become complacent. After we’ve completed a pre-flight inspection on the same aircraft a few dozen times, what do we really see? We perform the motions, but are we really looking and are we really thinking about what we are looking at.
The owner of a Piper Cherokee PA 28-140 had just had an annual inspection performed on his aircraft that included some work on the aileron bell cranks. Since he had not flown in three months, he asked another more experienced pilot to accompany him. At about 25 feet AGL, the aircraft started to roll left. The pilot applied right aileron to compensate, but the aircraft continued to roll left. The other pilot assisted in applying right aileron until full right aileron was applied. The aircraft continued to roll left and descended until it struck a snow bank beside a highway. The left wing separated and the aircraft came to rest in a field. Both pilots evacuated the aircraft with minor injuries.
The annual inspection on this Cherokee was performed by a very experienced mechanic and maintenance company owner. He discovered corrosion on the aileron bell cranks during this inspection. He performed the very arduous task of removing, repairing and re-installing the aileron bell cranks by memory.
He had completed similar tasks a few times recently and the microfiche reader with all of the instructions was some distance away.
He inadvertently interchanged the bell cranks when he re-installed them, reversing the ailerons. The final inspection of the work required that the ailerons be checked for correct movement and that a duel inspection be performed checking the aileron movement as well. Both he and a second mechanic signed the log book confirming the work was completed satisfactorily and inspected as required.
The aircraft checklist provided three opportunities for the pilot to check aileron movement; the pre-flight check, the before start check, and the before take-off check. The other pilot obviously was not monitoring the first pilot’s performance.
A charter company owner picked up a Cessna C-172 from another airport where a 100 hour inspection had been performed. The maintenance company owner had performed the inspection and was just finishing up when the aircraft owner arrived.
The maintenance company owner was called away to the telephone before he was finished and to speed the aircraft owner on his way, he asked another mechanic to finish the job for him. The second mechanic quickly looked over the engine and checked the oil. Everything appeared to be in order, so he replaced the engine cowlings and filled out the log book. The company owner glanced at the log book and signed it while still on the telephone.
The aircraft owner flew the aircraft back to home base over some very rough terrain. A few hours after his arrival at home base, another pilot reported the C-172 would not start. The aircraft owner removed the aircraft cowlings to check for a problem and discovered that three of the four spark plug leads were hanging away from the plugs.
A very experienced Beech King Air 100 pilot did not notice on his pre-flight inspection that the right engine cowling was not latched correctly on the front left side of the engine. During flight, the first officer noticed the right engine cowling start to rise. The crew landed at the nearest airport and secured the cowling.
The Cherokee and King Air pilots were not really looking or thinking about what they were looking at. The C-172 pilot saw the change in maintenance personnel taking place and assumed that an adequate hand over would occur. All of these experienced pilots were complacent.
All of the mechanics involved in these accidents and incidents were complacent as well. The first PA 28 mechanic relied on his memory and did not complete the travel inspection. The second PA 28 mechanic trusted that the boss wouldn’t make a mistake and therefore did not actually perform, or perform correctly, a dual inspection.
The first C-172 mechanic passed on his work to another mechanic without instructing him as to what work had been completed and what was still to be completed. The second C-172 mechanic did not check to find out where the boss actually was in the inspection before cowling up the C-172.
The Beech King Air mechanic did not confirm the cowling latches were all engaged before releasing the aircraft to the pilots. All of this is complacent behaviour.
We have a tendency to think that if an aircraft has just been inspected it is ready to go. This is complacency. We must remember that inspections are performed by people who may also get complacent and make mistakes.
Human factors courses state that human factors are involved in 80% of aviation accidents and 20% of aviation accidents are a result of mechanical or electrical failure. Who makes and installs the mechanical and electrical components? People. Therefore 100% of our accidents have a human component.
We should occasionally watch a student pilot or new pilot perform a pre-flight inspection on an aircraft. They will show us how it should be done.
Dale Nielsen is an ex-Armed Forces pilot and aerial photography pilot. He lives in Abbotsford, B.C., and currently flies air charters. He still freelances as a flying instructor and seminar facilitator. Nielsen is also the author of seven flight training manuals published by Canuck West Holdings.
Got an aviation safety story to tell? Dale Nielsen would like to hear from pilots who have educational aviation experiences to relate. Excerpts from these stories will be used in upcoming safety articles. Dale can be contacted via e-mail: firstname.lastname@example.org.