What happened
On July 16, 2009, a Robin DR 400-180, registration F-GDKT, was conducting a technical check flight following a 2,000-hour inspection at Toussus-le-Noble aerodrome. The pilot was performing various maneuvers, including climbs, descents, and stalls, when a loud noise was heard and a shadow appeared on the right side of the aircraft. The pilot discovered that the upper wing covering of the right wing semi-span had torn away. Although the aircraft became difficult to maneuver, it remained controllable. After notifying air traffic control and receiving landing priority, the pilot returned to Toussyl-le-Noble and landed on runway 07L without further incident. There were no injuries.
The investigation
The investigation focused on the structural integrity of the wing and the recent maintenance history of the aircraft. Investigators examined the right wing area, specifically the junction between the front spar web and the upper flange near the fuel tank. While the pilot had not noted any anomalies during the pre-flight inspection, the examination revealed tearing along the wing structure.
Laboratory analysis of fabric samples from the upper wing surface confirmed that the material met all manufacturer specifications and had not been degraded by ultraviolet radiation or chemical exposure. The mechanical properties of the fabric remained intact, and the adhesive bonding to the structure showed no defects. However, a detailed examination of the tear edges revealed that while some areas failed under high loads, other sections had been weakened by excessive abrasion of the fabric that was not visible to the naked eye.
Findings
- The primary cause of the incident was the inadequate preparation of the wing surface during a recent maintenance procedure, which included painting and the removal of silicone sealant during a major inspection.
- This maintenance work caused microscopic abrasion to the fabric, significantly weakening the wing covering.
- The aircraft had been repainted in 2002, though this specific operation was not documented in the aircraft's maintenance records.