ENG737

29th January 2024

Incorrect use of MEL

Initial Report

The flight crew arrived at the stand to find the aircraft only just arriving, having been towed over from the maintenance hangars. Crew boarded and commenced checks, shortly followed by line engineers, who were unhappy (but still helpful and working hard) at having had this aircraft dumped on them last minute. The engineers looked through the Tech Log and discovered a [system] deferred defect entry they weren’t happy about. The entry was made with a 10-day limitation, using MEL deferment authorisation.

The line engineer explained easily and in detail to the flight crew that this was not the correct MEL entry and that [component] was in fact a “no go” item. He showed on the system displays where the [component] was located and that how the procedure outlined in the MEL would be ineffective with engines running. He explained this would likely lead to a [Flight Deck] message either during take-off roll or in flight, which would then cause the aircraft to be AOG wherever it ended up. The engineers proceeded (under apparent pressure from engineering management over the telephone) to investigate the [defect], which had supposedly already been done in the hangar. They did not have the right steps equipment (due to the height needed to reach) and so had to make use of borescope equipment to try and establish [the source of the defect].

After some time, the engineers returned and explained the following to the flight crew.

They had confirmed the defect. They had looked up the information on this in the maintenance manual, where it explains that a specific piece of equipment is required to test the [system] to determine whether or not the [issue] is within limits for a dispatch or not. If out of limits, nil dispatch. If within limits, dispatch is allowed for a very limited number of sectors. They had then looked up whether [Operator] had that piece of testing equipment in stock, and they did not. Therefore, this required test cannot have been performed in the hangar, and the hangar had also clearly used the incorrect deferment authority and had not followed what the maintenance manual dictates, allows or recommends. This issue now went fully over to the senior engineering management and there was a period of time where everyone at the aircraft waited. The duty engineering manager arrived at the aircraft and requested the Captain operate the flight.

The Captain was aware of the information from the very experienced line engineer who had already said he would not want his signature stating this aircraft was airworthy. The Captain refused the manager’s request, who asked him once more, but then accepted the Captain’s decision. Service was then cancelled.

Too much pressure and [Aircraft Type] serviceability and parts availability is very concerning. So many ADDs, and worried how many are being correctly applied.

CAA Comment

[Operator] Engineering management have in general (not referring to this event) always stated that the Captain has the final word whether to accept the aircraft or not. The task was poorly planned into the hangar and accepted by the team in the previous shift because neither the test kit was arranged nor the task changed for the replacement of the [Component]; additionally, a replacement [Component] had not been arranged. The LAE who dealt with the input had 3 aircraft to deal with and delivery on time was a prime consideration for him. The engineer did state that he was not put under any pressure from Engineering Management however. He did not raise any issues of missing test kit with the [Maintenance Control] office and proceeded to do a test by an alternate method which was not in the approved data. He recorded the rectification by raising an ADD without any approved data reference. The test kit required had been sent for calibration in the first half of 2022 and returned. It was awaiting paperwork confirmation. Correct planning would have made arrangements for a [defect] tester to be available. Note; [Operator] have put a series of mitigations in place to prevent this happing again and the CAA will review when this is complete.

CHIRP Comment

The report was very comprehensive and detailed with the correct terminology and approved data references that had to be redacted for confidentiality reasons. Deviation from approved data references (AMM & MEL in this case) is a violation whichever way one considers it. The report investigation by the CAA focused on the poor decisions made in the hangar and the possibly perceived time pressure. Why does one fall into this trap? Is it because actual time pressure has now become so commonplace? Or, even though no management pressure was evident, perhaps peer pressure was at work? On the other hand, is perceived time pressure created or increased if colleagues seem to work at a slower rate than the Certifier/ Supervisor would like and therefore tries to compensate for? Happily, the Line Engineer did not line up the last hole in the cheese and, although the outcome was unfortunate, it was correct.