MEL Deferral, Check Due Date and a Certificate of Release to Service

Expiry

Indexing from the deferral date (4 March excluded): day 1 = 5 March … day 10 = 14 March. Rectification must be completed before the end of 14 March. Since the unit arrives on 13 March, there is a working day of margin - but the deferral must be closed out on the record, not merely 'assumed covered'.

Hours constraint - this is the trap

592 + 3.5 + 4.5 = 600.0 FH exactly. The aircraft reaches the 600 FH check limit exactly at the end of the second day's schedule. Any extra sector, any re-route, or any unplanned flight takes it beyond the limit and the aircraft cannot be dispatched until the check is done. The plan leaves zero margin, so the check should be brought forward or the second day's flying reduced.

If the part is late

• The MEL conditions may allow a single positioning/ferry flight to a maintenance base, but only if the MEL and the applicable rules provide for it and the competent authority's approval is obtained where required. Do not assume this.
• Otherwise the aircraft is not dispatched at all. The deferral expiring is not an extension opportunity; an MEL limit cannot be extended by the operator's own decision.

Yes, within the limits of the authorisation - and precisely scoped.

• The B2 holder may certify the maintenance they have performed, on the type and within the scope (avionics/electrical) and the category of work stated in the company authorisation, using the approved data.
• If the work falls outside their licence category, outside the authorisation, or requires base-maintenance facilities or a specific rating they do not hold, they cannot certify it; the organisation must allocate it to suitably authorised staff.
• A CRS certifies that the maintenance has been carried out in accordance with the approved data - it does not certify the aircraft's overall airworthiness. Airworthiness responsibility, continued airworthiness management and the MEL decision rest with the operator/owner.

Before flight with the VHF deferred, all of the following must be true:

1. The MEL entry is correctly completed - the exact reference and the conditions/limitations, with the appropriate placard fitted and any operational procedure applied;
2. The commander is informed of the deferred defect and the resulting limitations;
3. A CRS has been issued for the maintenance performed in applying the deferral;
4. The tech log and deferral record reflect the status.

MEL versus CDL

• MEL (Minimum Equipment List): derived from the MMEL and approved for the operator. It allows dispatch with specified equipment inoperative, subject to stated conditions and a time limit (categories A–D), while the aircraft otherwise conforms to its approved type design.
• CDL (Configuration Deviation List): covers missing external parts (fairings, seals, panels and similar items) that are not repaired before flight, with any associated performance penalties applied. It is part of the type design documentation, not the operator's MEL.
• A third category exists that must not be confused with either: items with no dispatch relief at all - those must be serviceable.

Records

• The deferral record and MEL entry, kept with the aircraft documents/tech log so the status is visible to the next crew and the next certifying staff.
• The CRS for the maintenance performed, and the certifying staff's employment/authorisation record, retained in accordance with the Part-145 record-retention requirements (typically 3 years for CRS and related maintenance records; verify the current rule set and the organisation's procedures).
• Details of the eventual rectification, including the part fitted and its release documentation, so the deferral can be closed and traceability maintained.
• Since the aircraft also reaches the 600 FH check, the check's own work pack, certification and any findings are separate records and must not be confused with the MEL file.