Pressurized skin crack at an antenna doubler after a hard landing
An AME is inspecting a pressurized twin turboprop after a reported hard landing recorded at 2.4 g. The fuselage skin is 1.0 mm 2024-T3, differential pressure is 9 psi, and the airframe has 28 000 cycles. Near a fuselage-mounted VHF antenna doubler, the AME finds an 18 mm radial crack starting at a doubler corner and a 0.8 mm deep, 40 mm long dent 60 mm aft. No corrosion is visible. The structural repair manual permits stop-drilling non-pressurized skin cracks up to 12 mm, but states that pressurized-skin repairs require an approved repair scheme. The operator wants to ferry the aircraft unpressurized at 8 000 ft to its base, 45 minutes away, where a Part 145 organisation can assess it. The aircraft is otherwise serviceable. The AME must decide what to do next and what to record.
1. Assess the crack, dent and hard-landing history. Is stop-drilling and ferry acceptable, and what conditions would you impose?
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The crack is at a doubler corner, a known stress concentration, and the 2.4 g event means the surrounding structure has seen additional load. An 18 mm crack exceeds the SRM stop-drill limit and is in pressurized skin, so stop-drilling alone is not an approved repair. The dent also matters: a 0.8 mm deep dent in 1.0 mm skin can hide cracking and reduce residual strength. I would not release the aircraft for normal service. For a ferry, I would first establish whether the crack is stable by cleaning and inspecting with eddy current, checking fastener holes and the doubler attachment, and confirming no crack growth toward a frame or stringer. A CAA special flight permit would be needed, with unpressurized flight, altitude and speed limits, no passengers, and inspection before and after the flight. If the crack is progressing or the doubler is loose, even a ferry is unjustified. The hard landing also requires inspection of gear attachments, engine mounts and wing-to-fuselage joints, not just the skin.
2. What inspection and analysis should be completed before return to service?
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Return to service needs an approved repair scheme from the OEM or an approved design, because this is pressurized-skin damage outside the SRM limits. Before that scheme is selected, I would remove the antenna doubler if the scheme requires it, inspect the fastener holes for elongation and cracking, and use eddy current around the crack tips and the dent. A tap test or ultrasound may help assess disbonding or hidden damage under the doubler, but the OEM method governs. The repair scheme should address crack arrest, load transfer and fatigue life, not just restore the skin. After repair, I would perform a pressurization leak test, inspect the repair under load, and record the repair, cycle count and any continued-airworthiness inspection. An independent inspection before release is prudent because the damage is in a primary pressurized structure.
3. Draft the documentation and approval path.
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The AME should record the hard-landing report, the crack and dent dimensions, the inspection methods used, and the SRM references in the maintenance record. The ferry should not proceed on a normal maintenance release. The operator should apply for a CAA special flight permit, supported by the damage assessment and the proposed flight limitations. The repair itself should be accomplished under a Part 145 organisation using an OEM repair scheme or an approved design, with the certifying staff confirming that the scheme is approved for this aircraft and configuration. The final release should reference the approved repair, the pressurization test, the independent inspection and any recurring inspection requirement. If the crack is classified as a major repair or major damage, the approval path must include the appropriate CAA acceptance rather than an AME's local judgement.