The 110-Hour Directive and the 300-Hour Check
5Y-CSA, a Cessna 208B Caravan, sits at Wilson Airport with 4,182 hours total time. An airworthiness directive applicable to the aircraft requires a detailed inspection of the elevator trim tab hinge fittings and hinge pin every 110 flight hours, with replacement of the pin if wear exceeds 0.003 inch. The last inspection is recorded at 4,074 hours. The operator's approved maintenance programme schedules the same inspection at 100-hour intervals. A 300-hour check is planned in roughly 30 flight hours, and the director of maintenance proposes to 'roll the AD inspection into the 300-hour check' to avoid a special visit to the hangar. Separately, the manufacturer has issued a service bulletin offering an eddy-current inspection at 220-hour intervals, and the DOM asks whether the AMO can adopt that interval now, without further formality, because the bulletin is 'approved data'.
1. Assess the DOM's proposal to defer the inspection to the 300-hour check. State what has already gone wrong and what must happen before the aircraft flies again.
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Compare the limits. The directive requires inspection every 110 flight hours; the last was at 4,074 hours, so 108 hours have elapsed. The approved maintenance programme requires the same inspection at 100-hour intervals.
Apply the more restrictive limit. Where an approved programme is tighter than the directive, the programme governs. At 108 hours the aircraft is already 8 hours beyond the programme interval, although still inside the directive interval by 2 hours.
Assess the proposal. Rolling the inspection into the 300-hour check would take the aircraft to about 138 hours since inspection, breaching both the directive and the programme. There is no engineering discretion to extend a mandatory interval for hangar convenience, and the DOM cannot authorise it.
What has already gone wrong. An 8-hour programme overrun occurred and must be investigated and recorded as a maintenance programme deviation, with the cause established and reported through the operator's continuing airworthiness procedures to KCAA.
Before further flight. Perform the inspection to the directive, measure and record pin wear, replace if beyond 0.003 inch, and only then certify. The aircraft is not airworthy for dispatch until this is done.
2. Can the AMO adopt the service bulletin's 220-hour interval immediately? Explain what 'approved data' does and does not mean, and the lawful route to a change.
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What approved data means. The bulletin is approved design data for the inspection method it describes: an engineer may use it to perform and certify the eddy-current inspection. It is not an instrument that amends an airworthiness directive.
Why immediate adoption fails. The directive is mandatory and its interval can only be changed by the State of Registry, or under an alternative method of compliance accepted by that State, typically after coordination with the State of Design. An operator, a DOM or an AMO cannot self-approve an alternative to a mandatory requirement, and commercial pressure is irrelevant.
The lawful route. Apply to KCAA for an alternative method of compliance, attaching the bulletin, the OEM recommendation, service experience and a proposed implementation date; obtain written approval that states the alternative inspection, the new interval and any conditions. Only then amend the approved maintenance programme to match.
Interim position. Until written approval is in hand, the directive as issued applies, together with the 100-hour programme interval. If the application is refused, the existing schedule continues unchanged.
3. Assuming the inspection is carried out at 4,182 hours, specify the records that must be raised and explain exactly what the certificate of release to service in this case certifies.
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AD compliance record. Directive number and revision, method used (detailed visual), findings including measured pin wear against the 0.003 inch limit, and the next due point. With the programme at 100 hours the next inspection falls at 4,282 hours; the directive alone would give 4,292 hours. Record the earlier figure, because the more restrictive limit governs.
Work documentation. Work order reference, task cards, any pin replacement with part and serial number and its release document, the engineer's name, licence number and signature, and the date.
Deviation record. The earlier 8-hour programme overrun, its cause and the corrective action, reported under the continuing airworthiness procedures to KCAA.
What the CRS certifies. That the maintenance recorded has been carried out in accordance with approved data and that, in respect of that work, the aircraft is airworthy. It is not a statement that every directive on the aircraft is complied with, and it does not validate the maintenance programme itself. If the AD status of the whole aircraft is being asserted, that belongs in the airworthiness review or the AD status statement, supported by the records above.