Composite Repair After a Ramp Impact
A business jet with carbon-fibre/epoxy wing-to-body fairings and a composite horizontal stabiliser leading edge sustains a ramp impact: a ground vehicle strikes the right stabiliser leading edge, leaving a 30 mm × 15 mm gouge with visible fibre breakage and some whitish 'milky' areas around it. The aircraft is otherwise undamaged. The structural repair manual classifies damage into categories: Category A (cosmetic, blend and seal), Category B (small, scarf repair by approved method), and Category C (requires OEM engineering). The SRM table gives a Category B limit of 25 mm in any direction for this zone. The operator has a charter in 8 hours and asks if it can be ferried to the main base (1 hour) for repair.
1. Classify the damage and state whether the ferry is permissible.
Read the worked answer
The gouge is 30 mm × 15 mm - the 30 mm dimension exceeds the 25 mm Category B limit in that zone. Visible fibre breakage plus 'milky' areas (possible delamination or matrix cracking) means this is not Category A (cosmetic). It is therefore at least Category C, requiring OEM engineering disposition.
Ferry decision: a permitted ferry may be possible under a specific ferry/positioning approval, but it cannot be treated as routine. You must:
- Confirm the damage is not in a primary load path or, if it is, obtain an OEM/design authority assessment or a specific ferry permit from the authority.
- Ensure the damage is stabilised (e.g. temporary protection/sealing per the SRM) to prevent moisture ingress and further delamination during the flight.
- The 8-hour charter is not a justification to fly an unclassified over-limit repair.
So: the charter as planned is not supportable; a controlled ferry for repair may be, subject to approval.
2. What does the 'milky' area around the gouge suggest, and why does it matter for the repair method?
Read the worked answer
Milky/whitish areas in carbon/epoxy indicate matrix cracking and possible delamination - the resin has failed or separated from the fibres, scattering light. This is damage beyond the visible gouge.
Why it matters:
- A scarf repair sized only to the visible gouge would leave delaminated material at the repair boundary, which will propagate.
- The repair must map the true damage extent - typically by tap testing or ultrasonic inspection - and the scarf must extend beyond the delamination.
- It changes the category: delamination may push the damage beyond Category B even if the gouge were smaller.
- It affects the repair design: the OEM must specify scarf ratio, ply lay-up and cure; a field patch is not acceptable.
So the milky zone must be inspected and included in the damage map before any repair is designed.
3. Assuming OEM engineering approves a repair, what quality controls must be in place for the bonded scarf repair?
Read the worked answer
A bonded composite scarf repair is a special process and needs full process control:
- Approved data: OEM repair scheme, materials, ply schedule, scarf ratio and cure cycle.
- Surface preparation: controlled abrasion, moisture drying, and contamination control - bond failures usually start at the interface.
- Material control: correct film adhesive and prepreg, within shelf life and stored correctly; log batch numbers.
- Environment: temperature and humidity within limits during lay-up.
- Cure control: calibrated equipment, recorded time/temperature/pressure; vacuum bag integrity check.
- NDT after cure: tap test or ultrasonic to confirm bond integrity and no voids.
- Trained and authorised personnel for composite bonded repair; the work must be signed by someone with the appropriate approval.
- Records: full traceability of materials, cure records, NDT results and the engineering approval.