Of Maintenance and Fatigue - John Goglia

 I recently wrote about an accident investigation conducted by the British equivalent of the NTSB that concluded that maintenance errors were the probable cause.  The accident was caused by the failure of mechanics to properly close and latch the engine fan cowl doors after routine overnight maintenance.  Both doors of the Airbus A319 subsequently detached on take off from London’s Heathrow Airport, substantially damaging the aircraft and resulting in an in-flight emergency.

In that article, I focused on the routine maintenance manual deviations that were highlighted by the accident investigation board that led to such a significant and potentially catastrophic event.  The article can be found here: https://www.ainonline.com/aviation-news/blogs/torqued-routine-manual-deviations-can-have-major-safety-consequences.  I mentioned that fatigue was considered a contributing factor but did not discuss its impact at length.  However, I do think it is important for mechanics to understand how fatigue can affect their performance. To me, it is as critical to understand why something happened as to understand what happened.  So, here the human factors report addresses a number of the whys behind the conduct of these mechanics on this particular maintenance job.

One of the findings of the human factors analysis was that the maintenance technicians “were at an elevated risk of fatigue on the night of the incident, having worked a considerable number of hours of overtime in the preceding weeks.”  This was determined to be a likely contributing cause of one of the errors involved in the engine cowling doors not being closed – the mechanics returned to complete work they had interrupted but returned to the wrong aircraft.  According to the report, this type of error is characterized as a “slip” – the mechanics intended to return to the correct aircraft but “their actions did not match their plan.”  According to the analysis, slips are typically the result of automatic actions, “well-practiced activities that are not consciously monitored.”  Fatigue can make these types of errors more likely because it reduces conscious monitoring of activities.

There are two particularly significant issues here for mechanics.  One is that fatigue can be cumulative.  The report points out weeks of overtime hours potentially affecting the mechanics.  While many workers either have no choice in working overtime hours – or welcome the extra pay – the important thing is for management and workers to acknowledge that that type of schedule can affect performance. 

The other finding of significance to mechanics is that fatigue risk can be managed through appropriate systems.  The report finds that the lack of a formal fatigue risk management system “meant that a key barrier to this type of error was not in place.”  While much focus has been placed on the impact of fatigue on pilot performance, much less focus has been placed on the impact of fatigue on maintenance workers.  This accident – and the careful analysis of human factors in the accident report – could be the one that finally causes airlines and safety regulators to see that fatigue risk management is just as critical for mechanics as for other aviation workers.  To read the report’s recommended strategies for combatting fatigue risk go to Appendix 6: https://assets.digital.cabinet-office.gov.uk/media/55a4bdb940f0b61562000001/AAR_1-2015_G-EUOE.pdf


"Fatigue can be cumulative." In a similar fatigue study on pilots, four groups were tested. One group got no sleep. They were useless after a day and a half, and knew it. A second group got four hours' rest per 24 hours. They, too, were gone after three days, and knew it. A fourth group got 8 hours' sleep each night, and remained useful indefinitely.

The third group was the interesting one. They got six hours of sleep each 24. At the end of four days, they performed as poorly as the no-sleep group, but they thought they were performing adequately!

Fatigue is also insidious.