The just-released accident report on the Airbus A319 that lost both doors on one engine’s fan cowl on takeoff from London Heathrow Airport in May 2013 is a must-read for anyone involved in aviation safety, whether at a major airline or manufacturer, at an air taxi or just flying or maintaining GA aircraft. The issues raised by the events leading to the accident, and as the events were unfolding in the airplane, affect many areas of aviation–from aircraft design to maintenance to pre-flight inspections to communications between cabin and flight crew during an in-flight emergency. But the most significant aspect of the report relates to maintenance and maintenance human factors. After all, it was maintenance errors that began the chain of events that ultimately led to the in-flight emergency.

In this accident, the precipitating factor was that the engine fan cowl doors detached on takeoff because they had not been properly closed and latched after routine overnight maintenance. The A319 was substantially damaged and the crew had to make an emergency landing. The accident report details not only the obvious failures to comply with maintenance manual procedures but also less obvious contributing factors that left the cowling doors unlatched, including the mechanics’ schedules and likely effects of fatigue. The report also highlights impediments to discovering the open doors during the pre-flight inspections by the crew and ground personnel. In addition, it makes recommendations for, among other things, changing the design of fan cowl door latches to prevent a recurrence.

For this long-time accident investigator and former airline mechanic, a well written and carefully analyzed accident report involving maintenance errors is more interesting than any summer thriller. This report is particularly captivating because no one was killed or even injured, although the accident could have had catastrophic consequences for the passengers and people on the ground around Heathrow. Despite the absence of fatalities, the accident report is as thorough and detailed as any I have read. Of course, the survival of the flight and cabin crews allowed them to participate in witness interviews. 

Human Factors

Without the enormity of a tragic loss of life, perhaps the maintenance technicians whose failure to latch the doors precipitated the accident were more candid with investigators. I was impressed with the apparent openness of the technicians in describing how and why the doors came to be left unlatched, even when that exposed them to criticism for not following procedures in the manual. It’s likely that the mechanics’ willingness to participate so candidly stems at least in part from the UK Civil Aviation Authority’s longstanding commitment to a just culture, where employees are not penalized for unintentional mistakes even when the consequences are as critical as they were here.

One of the real highlights of the report is the Human Factors Specialist’s Report, which focuses on the “human factors issues that influenced the performance of the maintenance technicians” the night the aircraft was left unsafe for flight the next morning and its log improperly signed off for work that had not been completed. This is one of the most comprehensive efforts I have seen to focus on the human factors that lead to critical maintenance errors. 

The human factors report raises a number of issues that have long concerned many of us in maintenance. I hope that seeing these flaws analyzed in the context of such a potentially catastrophic accident will force the FAA, the airlines and others involved in maintenance to spend time and resources working through them. Studying the whole report will provide valuable insights into compliance with detailed manual procedures, the use of written memory aids and the impact of mechanics’ schedules on fatigue and human errors.

One of the most significant issues for me is how seemingly minor deviations from the maintenance manual can–in all the wrong circumstances–lead to an accident. In this case, the mechanics intentionally did not close and latch the fan cowl doors or leave them in a clearly open position, even though the maintenance manual required them to. The reasons for not doing so are common: the procedures are cumbersome to follow and the mechanics were going to return to complete the work they had begun but needed to get the appropriate tool. In addition, they substituted their own judgment about the best way to leave the doors unlatched instead of following the manual’s directions. Among the “small” items skipped that could have prevented this near tragedy was the placement of a required warning notice in the cockpit to alert the crew or other mechanics that the cowling doors were open. The human factors report calls these “routine” violations because they “are a common occurrence amongst many operators.”

The mechanics did in fact return to complete the work, but markings on the ramp and placement of the logbook caused them to return to the wrong aircraft. While technicians knew of other instances of work being done on the wrong aircraft, management seemed unaware of the problem.

This mishap clearly demonstrates why maintenance culture has to change so that deviations from manual requirements–no matter how small–are not tolerated. At the same time, problems identified by mechanics in maintenance-manual procedures or in routine maintenance operations (such as work being performed on the wrong aircraft) have to be flagged and addressed immediately, backed by a commitment from the executive suite all the way to the shop floor. 

While I am not familiar with the maintenance culture at this particular base, all too often I have seen managers and executives “winking” at procedural deviations in the interests of moving work more “efficiently.” Management needs to have a presence on the shop floor and routinely audit work to ensure that detailed work steps are followed every time. Complying with detailed maintenance manual requirements takes time. So while I believe mechanics need to take responsibility for complying with each detailed step every time maintenance is performed, they need management that supports them by allowing them time to attend to all the details required to do a job correctly.