Ambiguous MEL Deferral and the 'Already Deferred' Pressure
An AME on night shift is reviewing a defect entry for a twin turboprop: 'Pressurisation erratic in climb, ops normal after level off.' The aircraft is under an MEL that allows operation with the pressurisation system inoperative, provided a specific procedure is used. The previous shift has already written 'MEL applied, category C, 10 days' and placed a placard. The AME notices the entry does not identify the defective component or confirm the system was isolated. The crew is due at 05:30 and the operations controller says the aircraft is 'already deferred, just sign the release'. The AME has no troubleshooting support at night and the MEL requires an operational check before dispatch.
1. Is the existing MEL deferral valid? Justify your answer with reference to the entry and the MEL conditions.
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The deferral is not valid on the evidence in the log. An MEL category C interval gives a permitted repair period, but it does not by itself make the aircraft airworthy. The entry describes a symptom, 'erratic in climb', but does not identify the defective component, confirm that the system has been isolated, or show that the required operational procedure has been accomplished. The MEL requires specific conditions, including an operational check before dispatch, and those conditions are not recorded. 'Ops normal after level off' is ambiguous and does not prove the system is deactivated. A placard alone is not a substitute for the technical action. The previous 'MEL applied' entry is a claim, not evidence. The AME should treat the deferral as incomplete and not rely on it.
2. What actions should the AME take before signing any maintenance release?
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The AME should not sign the release on the current paperwork. They should first contact maintenance control or technical support to identify the defective component and the correct MEL procedure. If the system is to be deferred, the AME must confirm the isolation or deactivation step, fit the required placard, amend the log with the specific defect and the MEL reference, and complete the operational check required by the MEL. If troubleshooting support is not available at night, the aircraft should remain grounded until it is. The AME should document the conversation with the operations controller and escalate if pressure continues. The release should only be issued when the MEL conditions are actually met, not when the aircraft is merely labelled 'deferred'.
3. How could communication between shifts have reduced the risk in this case?
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A structured handover would have required the outgoing shift to state the defect, the suspected component, the MEL reference, what had and had not been done, and what the incoming shift must verify. A read-back by the incoming AME would have exposed the missing isolation and operational check before the aircraft reached the departure gate. The log entry should use a standard format rather than 'ops normal', and the placard should reference the specific MEL item. The operations controller should have been told at handover that the aircraft was not released pending verification, not that it was 'already deferred'. A shift supervisor or maintenance controller should own the open item and record it in the handover sheet. Good communication would have converted an ambiguous verbal assumption into a clear, auditable hold point.