Composite Flap Delamination Near the Hinge Line
During a flap inspection on a composite-skin airplane, you find a 1.5 in by 0.8 in delamination in the upper flap skin near the trailing edge. There is no through-penetration and no visible lightning-strike damage. The SRM allows a bonded scarf repair for delaminations up to 1.0 in in the largest dimension, provided the damage is at least 2.0 in from the hinge line and not in a lightning-strike zone. The damage is 1.2 in from the hinge line. The flap is a primary flight control with a 6,000-hour inspection interval; the aircraft has 4,200 hours. The operator wants a field repair to avoid downtime.
1. Is the SRM bonded scarf repair allowed for this damage? Justify the answer using the stated limits.
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No. The SRM repair is limited to delaminations up to 1.0 in in the largest dimension. This damage is 1.5 in in its largest dimension, so it exceeds the size limit. In addition, the repair requires the damage to be at least 2.0 in from the hinge line, but this damage is only 1.2 in from the hinge line. Both the size and proximity limits are violated.
The fact that there is no through-penetration and no lightning-strike damage does not make the SRM field repair applicable.
2. What disposition is appropriate, and why can't the operator simply perform a field repair?
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The damage requires engineering disposition or a repair approved by the OEM or a DER. A field repair using the SRM scarf procedure is not permitted because the damage exceeds the SRM limits and is close to a primary flight-control hinge area. The hinge region carries concentrated loads, and an unapproved repair could affect flutter characteristics, load distribution, and fatigue life.
The operator should obtain approved repair data, accomplish the repair, and document it. Downtime pressure does not justify an unapproved repair.
3. What follow-up inspection and documentation should be required after the repair?
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After the approved repair:
- Inspect the repaired area by the method specified in the approved data, such as tap testing, ultrasonic inspection, or visual inspection.
- Verify bond-line integrity and contour as required.
- Perform a functional check of the flap through its full travel and confirm rigging.
- Record the damage dimensions, location, repair method, and inspection results in the maintenance records.
- If the repair is major, complete FAA Form 337 and obtain the required approval.
Because the flap is a primary flight control, the repaired area should also be included in future inspections as directed by the approved data.