Troubleshooting, BITE and the Minimum Equipment List

Troubleshooting is a discipline, not a guess. Confirm the reported fault and every system it affects, isolate to the smallest possible area, test the suspected cause non-destructively, then verify the repair. A fault tree narrows the search deliberately; swapping parts at random is not isolation and can destroy evidence.

Built-in test equipment gathers parameters and stores fault codes on the aircraft. Read the fault history as well as the current codes, because a code describes what the system saw, not necessarily what is broken now, and an intermittent symptom is often the more useful record. Correlate the code with the maintenance manual fault-isolation procedure rather than acting on the code alone.

The minimum equipment list is an approved document that permits dispatch with a specified item inoperative, under stated conditions and for a limited repair interval. The configuration deviation list covers items that may be missing or different from the certificated configuration. Neither document permits an unapproved deferral, and a MEL item is never a substitute for a repair — the item is restored or the aircraft does not fly.

Some work is subject to independent inspection, and some removals are not to be accomplished while the aircraft is powered or with passengers aboard. Secure the aircraft within its documented limits before any heavy maintenance, and record the deferral, the reference and the signature in the aircraft record.