Both the US Federal Aviation Administrator (FAA) and the European Union Aviation Safety Agency (EASA) have issued airworthiness directives for the Boeing 757. The directives mandate any operators of this aircraft type to inspect the aileron actuators of 757s within 1,760 flight hours, or around six months, from the effective dates of the directives, which was the 12th July.
The orders from the FAA and EASA come following an in service report of an issue with the functionality of the component. Reportedly, the issue limited a flight crew’s ability to move the flight control surfaces.
Boeing had previously recommended an inspection with their service information issued in late March. However, Boeing service information guidance is optional for operators. Now, with ADs issued by both EASA and the FAA, operators of the type must comply with the inspection request.
An in service incident
These directives come following an in service incident on a Boeing 757 which limited the crew’s ability to control the plane. The flight crew found they were unable to move the ailerons using the trim wheel. Boeing reported the incident to the regulator and issued guidance for inspections in its March service information update.
According to the details of the airworthiness directive, the FAA says that,
“The FAA received a report indicating that a flightcrew could not center the ailerons with a left or right turn on the aileron trim control wheel during a flight control check. Maintenance personnel found that the aileron trim actuator attachment lug had broken off of its support box assembly but was still attached to the aileron trim actuator.
“Stress analysis found that the separation of the lug could have been the result of seizure of the aileron trim actuator bearing, which would exert forces on the attachment lug that could be higher than what it is designed for. The lug failure resulted in a free-floating aileron trim actuator and subsequent loss of feel force, wheel centering, and lateral trim. This condition, if not addressed, could cause over-control of the airplane and subsequent lateral pilot induced oscillations (PIO), which could adversely affect continued safe flight and landing.”
Often, the FAA will issue a notice of proposed rulemaking (NPRM) prior to publishing an AD, which allows time for public comment on the proposals. However, in their briefing, they state that to allow comments, and then to consider those comments, would reduce the time allowed for compliance. This, they say, could lead to a grounding of some aircraft, and could cause significant disruption to certain operators.
The cost of compliance
As well as performing an initial inspection within 1,760 flight hours of the 12th July, the FAA has also, on the recommendations of Boeing, stated that repeat inspections must be carried out every 1,100 flight hours. Operators need to look out for cracking or damage to the aileron trim actuator attachment, carrying out remedial work as necessary.
According to FAA data, the costs associated with these checks are three work hours. Based on an $85 per hour cost for this, each inspection will cost operators $225 per plane. Should remedial work we required, the cost of replacing the part is estimated to be four work hours plus a part cost of $17,693, bringing this total to $18,033.
Despite the production of the 757 stopping over 15 years ago, there are still a large number in service. North America is home to the biggest numbers of the type, with MRO Network estimating 451 of the 667 still in service to be operated in North America. The largest operator of the type is Delta Air Lines, which has 112 in its fleet.
Taking Delta as an example, each inspection round of their 112 aircraft will cost the airline $25,200. If all required replacement parts (an unlikely scenario but possible), the cost to replace them all would exceed $4m.
Boeing has identified the issue as being caused by a seized actuator bearing. The manufacturer is working on a replacement part which will be rolled out to operators when ready. Until then, repetitive checks are required ongoing.