The AD Interval Conflict, the 2,940-Cycle Freighter and the Untagged Pump
A Lagos-based cargo operator flies a 5N-registered Boeing 737-300SF that has accumulated 2,940 flight cycles since its last major check. The FAA, as State of Design, has issued an airworthiness directive requiring repetitive eddy-current inspections of the fuselage lap joints at intervals 'not to exceed 3,000 flight cycles', with terminating action available through a Boeing service bulletin. The airline's NCAA-approved maintenance programme, last revised in 2018, lists the same inspection at 4,000 cycles, based on an older MPD revision. Planning has scheduled the inspection for next month, roughly 60 cycles away. At the same check a replacement hydraulic pump arrives from a broker with only a certificate of conformity; the stores supervisor says the previous pump arrived the same way and 'nobody complained'. The certifying engineer is under pressure to sign the certificate of release to service tonight because the aircraft has a Sharjah charter at 22:00.
1. Which inspection interval governs, and can the aircraft be released tonight for the Sharjah charter?
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The airworthiness directive governs. An AD issued by the State of Design is made mandatory in Nigeria through the Nig. CARs airworthiness provisions, which implement the continuing airworthiness obligations of Annex 8. An AD interval expressed as 'not to exceed' is a hard limit; an approved maintenance programme cannot relax it, and a conflict between the programme and the AD is resolved in favour of the more restrictive requirement.
At 2,940 cycles the AD is not yet overdue, so the aircraft is not automatically grounded. But three things must happen before a release:
- The AD status must be verified against the actual records and the next due cycle calculated, not assumed.
- The planned charter must be checked against the remaining 60 cycles. Lagos–Sharjah–Lagos involves relatively few cycles, so the limit is likely to be covered, but that has to be demonstrated, not guessed, and the inspection must be scheduled before the limit is reached.
- The programme discrepancy must be corrected. Operating to an NCAA-approved programme that undercuts a mandatory AD is itself a breach, and the programme requires revision and NCAA approval or acceptance of a temporary revision before the next flight.
If the remaining cycles cannot cover the planned operation, the aircraft does not go. The engineer should record the AD compliance position accurately in the maintenance records and not sign a release that hides the programme conflict.
2. Can the hydraulic pump be fitted and released with only a certificate of conformity?
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No. A certificate of conformity is a manufacturer's or supplier's statement that an item was produced to a specification; it is not an airworthiness approval. For a type-certificated part going onto a Nigerian-registered aircraft, the engineer needs an authorised release document from an approved organisation - in the Nigerian system an NCAA Form 1, or an accepted equivalent such as an EASA Form 1 or FAA 8130-3 under the applicable bilateral arrangements - identifying the part number, serial number, approved design data and the organisation issuing it.
Without that, traceability is unproven and the part must be treated as a suspected unapproved part: quarantine it, do not fit it, do not certify it, and raise an internal report so the operator can investigate the supply chain. The remark that 'the previous pump came the same way and nobody complained' is not reassurance; it converts one suspect part into a fleet-wide traceability problem that should be reviewed, because the previously installed pump may also lack acceptable documentation.
The CRS for tonight can only be signed once a compliant pump with proper release documentation is fitted and all other tasks are complete. Stores pressure is not an airworthiness argument.
3. What should the engineer record and escalate, and what regulatory action should the operator anticipate?
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Recording is the engineer's protection and the operator's evidence base. He should write the AD compliance status as it actually stands, with the cycle count, next due and the programme discrepancy; record the pump rejection with the broker's documentation reference; and record his refusal to release pending resolution, not a vague 'awaiting parts'.
Escalation should go to the quality manager and the accountable manager in writing, with the NCAA informed where the exposition requires it. The suspected unapproved part is a safety occurrence and should be reported through the operator's occurrence reporting system.
The operator should anticipate: an NCAA review of why an approved programme carried a 4,000-cycle interval against a 3,000-cycle AD; findings against the maintenance programme control process; and enforcement action if any aircraft was operated outside the AD limit. The parts issue may trigger a wider unapproved-parts investigation covering previous installations and other components from the same broker. Voluntary disclosure and a credible corrective action plan are the operator's best route to a proportionate outcome; concealment discovered later is treated far more severely.