What happened
On 17 June 2007, an Avro 146-RJ85, registration OH-SAI, was descending to below FL200 while inbound to Stansted when the flight crew heard a loud bang. The crew noted a change in airframe noise and a requirement for slight additional right trim. Following standard procedures, the descent to Stansted was continued, and the crew deployed the flaps and landing gear slightly earlier than usual to verify the aircraft's normal operation. The aircraft landed without further incident.
Upon parking, the crew discovered that a panel from the wing-to-fuselage fairing was missing and the fin had sustained minor damage. The detached panel had landed on the roof of a house in the village of Stratford St Andrew, Suffolk, causing minor damage to the structure. No injuries were reported to the 83 passengers or the 4 crew members on board.
The investigation
Investigators examined the detached panel and found no evidence of damage to the area surrounding the attachment holes. An inspection of the corresponding panel on the right wing revealed that the stainless steel grommets and bolts had been painted, making them difficult to inspect. After stripping the paint from these grommets, investigators found that four areas had a flange thickness below specification and showed signs of abrasion.
Further examination of the aircraft's maintenance history showed that the fuselage had been stripped and the composite panels abraded during a full repainting process just 11 weeks prior to the incident. While the bolts remained in their respective grommets, the upper flanges of all 25 grommets had failed.
Findings
- The detachment of the panel was caused by the failure of the stainless steel grommets.
- The failure was attributed to the reduction in flange thickness caused by abrasion during the repainting process.
- The presence of paint on the grommets had previously obscured the ability to detect this thinning during inspections.
- The manufacturer had recorded nine similar occurrences involving panel attachment issues in this aircraft family.