Vertical Fin Spar Crack on an AS350 B2 After a Hard Landing
During a 100-hour inspection on an AS350 B2, you find a 22 mm crack emanating from a rivet hole in the upper vertical fin spar where the horizontal stabilizer attaches. The aircraft has 6,840 airframe hours and 12,350 landings. The operator reports a hard landing two weeks earlier and wants the aircraft released for a heli-ski charter in 36 hours. The SRM has a repairable damage category for cracks up to 25 mm at that location, but the approved repair scheme calls for special close-tolerance rivets and post-repair NDT. The special rivets are not in stock; standard MS rivets are available. The previous hard-landing inspection entry says only 'checked, no defects', and you have no jig or replacement spar. You are the only licensed AME on site.
1. Classify the crack and decide whether the aircraft can be released using the standard rivets. Explain the structural and airworthiness reasoning.
Read the worked answer
The crack is in a primary structural element at a stabilizer attachment, so it cannot be treated as a minor defect. The SRM's 25 mm limit is not a blanket permission to repair: it defines a repairable damage category only when the approved repair scheme is followed. The scheme specifies close-tolerance rivets because the joint is load-critical and the rivet holes are likely cold-worked or interference-fit. Substituting standard MS rivets changes the load transfer, hole fill and fatigue life, and is not approved data.
Therefore the aircraft is not airworthy for release with a standard-rivet repair. Options are: obtain the specified rivets and approved repair data, or replace the spar or fin with a serviceable assembly. Until then, the aircraft should be placarded or immobilised. A 36-hour charter deadline is commercial pressure and does not change the technical decision. If the crack grew from the hard landing, the inspection entry 'checked, no defects' also needs review because it may indicate an inadequate inspection.
2. The operator asks you to install the repair using the standard rivets 'just this once' and sign it off. What do you do, and what documentation and approvals are needed?
Read the worked answer
I would refuse to sign off an unapproved repair. Signing a maintenance release certifies that the work was done in accordance with approved data, and an unapproved rivet substitution would make that certification false. The correct path is to raise a defect, quarantine the aircraft from service, and advise the operator in writing of the required corrective action.
Documentation should include: the inspection finding with crack location and size; reference to the SRM damage category and repair scheme; a defect entry; and a statement that the aircraft is not released. If a repair is later designed by an approved engineering organisation, that organisation must provide approved data, and the rivet type, hole preparation and NDT must match it. The completed repair should be recorded in the airframe log with reference to the approved data, and a dual inspection or independent check should be considered for a critical attachment. Any deviation from the SRM scheme needs an approved alternative.
3. What post-repair inspections and operational limitations would you expect before return to service?
Read the worked answer
After an approved repair, I would expect: verification that the specified rivets were used and correctly installed; hole condition checks before riveting; and the NDT called for by the repair scheme, likely eddy-current or dye-penetrant inspection around the attachment and adjacent holes. Torque and locking of stabilizer attachment bolts would be checked. A rigging and alignment check of the horizontal stabilizer should confirm symmetry and clearances.
Before release I would want a maintenance test flight or a functional check as required by the approved data, with attention to vibration, trim and tail response. The aircraft should then be returned to service with any SRM flight limitations, inspection intervals or reduced life items recorded. I would also add a short-term follow-up inspection if the repair scheme requires it. Finally, the hard-landing event should be assessed against the manufacturer's hard-landing inspection criteria, not just the crack location, because other attachments or the tail boom may have been affected.