MEL Dispatch Decision with an Unserviceable Item
You are the B1 certifying engineer at a Gulf station. An A320 has an unserviceable left-hand landing light and a failed cabin emergency lighting battery pack (one of two). The operator's Minimum Equipment List (MEL) permits dispatch with one landing light inoperative under a specific operational condition, and permits one emergency lighting battery pack inoperative only if the remaining pack is verified serviceable and the MEL's rectification interval is respected. The captain wants to depart with both items deferred. You must decide whether to issue the Certificate of Release to Service and how to record the deferrals.
1. How do you determine whether the aircraft may be dispatched under the MEL?
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The MEL is part of the operator's approved documentation and must be applied exactly. For each item:
- Locate the MEL entry for the landing light and the emergency lighting battery pack.
- Check the conditions (O), (M) and rectification interval (A/B/C/D) - e.g. whether an operational procedure or maintenance action is required before dispatch.
- Verify the remaining system - for the emergency lighting pack, confirm the second pack is serviceable (test per AMM) and record the result.
- Confirm the rectification interval is not exceeded and that the deferral is within the category limit.
Only if all conditions are met may the item be deferred and the CRS issued. If any condition fails, the aircraft is not dispatchable under the MEL.
2. What must be recorded in the technical log and by whom?
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Record in the technical log / deferred defect record:
- the defect description and the MEL reference (item number, category, rectification interval);
- the maintenance action taken (e.g. emergency lighting pack test result);
- any operational (O) procedure to be observed by the crew;
- the name, licence number and signature of the certifying B1 engineer;
- the date and, if applicable, the due date for rectification.
The captain/operator is responsible for observing the (O) procedures; the certifying engineer is responsible for the (M) actions and the release. Both must be documented - an undocumented deferral is not a valid deferral.
3. If the emergency lighting battery pack cannot be verified serviceable, what is your decision?
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If the remaining pack cannot be verified serviceable, the MEL condition is not satisfied, so the item cannot be deferred. The aircraft must not be dispatched for revenue service until the pack is replaced or the system restored to a serviceable condition. You should:
- refuse the CRS;
- record the reason;
- inform the captain and operator;
- arrange rectification or a permitted ferry under a specific authorisation if the NAA allows.
Commercial pressure does not override the MEL conditions.