The Cessna 172 was on a VFR flight carrying four people when, at an altitude of 5500ft ASL, the right-hand aileron yoke assembly came apart, and the pilot lost lateral control. He immediately declared an emergency and the control centre guided him to the airport, where emergency services were standing by. The elevator was functioning normally, but the pilot used it as little as possible for fear that the flight controls might jam completely. He successfully landed without incident and no one was injured.
Four days before this last event — following the annual inspection of his aircraft, the pilot took off at about 16:45 eastern daylight time (EDT). Approximately 13mi. away, at an altitude of 2700ft, the pilot noticed that the aileron control was no longer responding. Using the elevator, its trim tab, and the rudder, the pilot managed to turn back and set the aircraft down on the runway. The landing proceeded without incident, and the pilot did not declare an emergency.
When the pilot arrived at the hangar, all the the employees, except for the maintenance manager, had left the premises. The maintenance manager checked the malfunction and found that the right-hand aileron yoke assembly had come apart and that some parts had fallen onto the floor of the aircraft. He re-did the work himself. The pilot’s lack of a night rating put additional pressure on the maintenance manager, who rushed to complete the work before it began to get dark. He put the universal joint back in place, checked the operation again, and returned the aircraft to service without making technical entry and without asking anyone else to perform an independent inspection. The pilot took off again at about 18:25EDT, and the flight proceeded without incident. The maintenance manager, who was involved in the work, had over 20years of experience in aircraft maintenance. During the 7April 2000 annual inspection, an apprentice technician had taken part in the installation of the aileron control system, and the maintenance manager had checked the work. Yet the aircraft had been returned to service with the aileron yoke assembly incorrectly installed.
The work on the yoke involved rotating two identical parts from one side to the other of the flight control to the other. The two mechanisms were similar, but access to the right side was restricted by the presence of radio equipment and the card box. This work was simple enough for the maintenance manager to allow an apprentice technician, who had only one year of experience, to perform the work without constant supervision. The apprentice technician was, however, supervised by a more experienced apprentice technician. For economic reasons, the maintenance manager had suggested to the aircraft’s owner that the universal joints be rotated instead of just replacing the left joint. By so doing, he increased his maintenance staff’s workload, and the risk of error, without contravening the regulations. The pilot performed a pre-flight check, and all the flight systems were functioning normally. Aeronautical maintenance professionals require a number of skills and are subject to a variety of pressures. Among other things, they have to keep aircraft airworthy, perform maintenance on an ageing fleet, and cope with other stress factors that affect their performance. The serious consequences of a flight or engine control installation or adjustment error are well known to the industry and to Transport Canada. That is why engine- and flight-control maintenance is treated differently from other maintenance work, in that an independent inspection is required on completion of such maintenance work. In both occurrences, no entry certifying that an independent inspection had been done was made in either the aircraft journey log or any other technical log. The investigation revealed that, in both occurrences, the aileron control system had been incorrectly installed, resulting in the aircraft’s loss of lateral control in flight.