The MEL, the AD, and the Transatlantic Trip
You are director of maintenance for a Part 135 operator with one available G450. On Tuesday a pilot reports the left air data computer inoperative. The MMEL permits dispatch with the right ADC supplying both pilots' displays, but prohibits RVSM operations and requires an (M) procedure to be accomplished and an (O) procedure to brief the crew. The deferral was issued on day 2 of a 10-day MMEL limit. On Thursday the aircraft is scheduled for KHPN–EGLF with eight passengers; the North Atlantic tracks require RVSM, and the drift-down and contingency planning assume FL430. Separately, an airworthiness directive requires inspection of the horizontal stabilizer trim actuator at intervals not to exceed 1,200 flight hours; the aircraft is at 1,187 hours and the trip is planned at 22 hours. The chief pilot wants your sign-off and says the account will move if the trip cancels. The DOM's proposal on the table is: “The MEL gives us 10 days, so sign it off and go; we'll do the AD inspection when we're back.”
1. Can the aircraft legally be dispatched on the trip as planned? Address RVSM and the AD separately.
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No - on two independent grounds, either one of which is sufficient to ground the mission.
RVSM. The MMEL allows dispatch but explicitly prohibits RVSM. An operator's MEL may not be less restrictive than the MMEL, and the FAA has to approve any deviation; a DOM cannot waive it. North Atlantic tracks are RVSM airspace, so the planned routing is not available. Flying below RVSM in the NAT is not a workaround - the contingency and drift-down plan is built on FL430, and non-RVSM operations in that airspace require prior approval that this trip does not have. The (M) and (O) procedures must also be properly accomplished and briefed, which they have not been.
AD. The inspection falls due at 1,200 hours; the aircraft is at 1,187 and the trip consumes 22. The AD becomes overdue roughly 9 hours into the mission. An AD is not deferrable under the MEL, and there is no operator discretion to extend the interval - only an FAA-approved alternative method of compliance or an approved change to the AD changes the requirement. There is no such approval here.
Signing an airworthiness release for this flight would be a false record under 14 CFR 43.9/43.16 and 135.443, and would expose the mechanic and the certificate holder. The answer to the chief pilot is no, and it is not a close call.
2. What are the operator's real options, and what approval or documentation does each require?
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Four options, in order of preference:
- Fix the airplane. Swap or repair the ADC from stock or AOG service, and accomplish the AD inspection. The AD inspection is likely a few hours of work if tooling and a qualified inspector are available; the ADC is an LRU if one is on the shelf. Thursday is two days away - this is the first call, not the last.
- Do the AD, ferry the airplane non-RVSM only if approved, and re-plan the mission. A special flight permit under 14 CFR 21.197/21.199 allows flight for maintenance or delivery, but it does not authorize carrying passengers for hire; it also will not solve an RVSM restriction for a revenue transatlantic leg.
- Subcharter. Place the passengers on another operator's aircraft. Costly, but the certificate survives and the client is served.
- Cancel or delay and manage the account honestly. Cheaper than an enforcement action, a violated NAT track, or an overdue AD discovered by an inspector.
For any MEL deferral that does proceed, the file must show the placard, the log entry citing the MMEL item, the (M) procedure signed off by properly rated personnel, the (O) procedure briefed to the crew, and the calendar-day count of the 10-day limit. Never let a ferry permit be used as a passenger workaround.
3. What do you tell the chief pilot and the client, and what systemic fix prevents a repeat?
Read the worked answer
To the chief pilot: state the two blockers in one sentence each - the MMEL prohibits RVSM on a NAT track, and the AD is due inside the trip's block time. Offer the subcharter option the same day so he has something to take to the client. Make clear the answer is not a negotiating position.
To the client: a single, factual message from one voice - an airworthiness limitation prevents the flight as scheduled, here is the alternative, here is the decision time. Do not let the crew carry the message, and do not blame the mechanic.
Systemic fixes:
- Build a maintenance look-ahead into trip quoting: any AD or inspection falling due within 110% of the planned block time is flagged before the trip is sold, not the week of.
- Add an MMEL cross-check to the trip-planning checklist for RVSM, RNP, and approach capability, with the routing already known.
- Keep a small AOG spares and vendor list for high-removal-rate LRUs like ADCs.
- Publish a one-page rule that the MEL interval is a calendar limit set by the FAA-approved document and cannot be extended internally by anyone, including the DOM.
The real failure here is scheduling that consumed the entire maintenance margin, not the ADC.