Structural Crack Beyond SRM Limits: No MEL, No CRS
During an A check on a 12-year-old ATR 72-600, an NDT technician finds a 38 mm crack in a wing spar fitting. The SRM permits cracks up to 25 mm using a trim repair; for cracks beyond 25 mm it states 'contact manufacturer'. The operator's MEL includes no structural damage item, but the maintenance controller suggests deferring the defect under MEL 57-10 or positioning the aircraft to main base under a ferry flight. The next flight is a 45-minute non-revenue positioning flight with no passengers. The aircraft is at a line station with no structural repair team; the manufacturer's engineering desk is closed until Monday, and it is Friday evening. The certifying engineer is asked to sign the CRS so the aircraft can be ferried. He has a copy of the SRM and the NDT report. The operator says the aircraft will be grounded at main base until repaired.
1. Can the crack be deferred under the MEL? Why or why not?
Read the worked answer
No. An MEL is derived from the MMEL and covers equipment and system defects that can be deferred with defined operational and maintenance procedures; it is not a structural repair manual. A 38 mm crack in a wing spar fitting exceeds the SRM limit of 25 mm and means the aircraft no longer conforms to its type design in a primary structural element. There is no MEL item that can make that airworthy. The maintenance controller's suggestion of MEL 57-10 confuses a structural defect with a system item. The aircraft is unairworthy until an approved repair is designed and embodied, or until CAAM authorises a special flight permit for a ferry flight. The certifying engineer should reject the MEL route and record the SRM reference and the NDT finding.
2. Can the aircraft be ferried, and if so, under what authority and conditions?
Read the worked answer
Possibly, but not under a normal CRS and not under the MEL. A ferry flight requires a CAAM special flight permit or ferry flight authorisation, issued for a non-revenue flight to a maintenance base. The operator must apply, and CAAM will set conditions based on the defect: route, altitude, speed, weather, crew, no passengers, and any inspections before and after the flight. The manufacturer's engineering desk should be consulted if available, even after the weekend, because the permit may depend on a documented structural assessment. The AMO should not assume that a 45-minute flight is automatically acceptable; the crack could propagate. The certifying engineer can only release the aircraft for the ferry flight if the permit conditions are met and he is authorised to do so. The record must reference the permit, not a standard CRS for revenue service.
3. What should the certifying engineer do with the CRS and the records?
Read the worked answer
He should not sign a CRS for revenue service. He should document the NDT result, the SRM limit, the fact that the crack exceeds it, and the manufacturer's 'contact manufacturer' instruction. If a ferry permit is obtained, he should ensure the aircraft is released only for the permitted flight, with the permit attached to the work pack and the logbook entry clearly marked as a ferry release. He should notify the operator's continuing airworthiness manager and, if required, CAAM. He should also ensure the aircraft is not returned to service after the ferry flight until the repair is approved and certified. The records should allow a later reviewer to see why the aircraft was grounded and how the ferry flight was authorised.