What happened
On 23 July 2004, a Fairey Britten Norman BN2A Mk III-2 ‘Trislander’, registration G-BEVT, operated by Aurigny Air Services, was performing a takeoff from Guernsey Airport. Approximately four minutes into the flight, a loud bang was heard inside the cabin. A passenger informed the commander that a window had shattered and that two passengers had sustained injuries.
Following the alert, the pilot decided to return to the airport. Upon landing and disembarking the passengers, the pilot observed that a de-icer boot from the left-hand propeller had detached and was resting on a seat inside the cabin, adjacent to the broken window.
The investigation
The investigation focused on the left-hand propeller, which was equipped with a BF Goodrich de-icing system. While the installation was documented as being completed according to the appropriate manual, investigators found that the required filler material had not been applied during recent maintenance work. This work had been performed to replace a defective harness guard and restrainer strap.
Laboratory analysis revealed that a small area of the lead strap, outboard of the restrainer strap, was unbonded. This gap allowed moisture and contaminants to enter, which degraded the adhesive bond over time. The investigation also noted that for a period, the necessary filler material was commercially unavailable in the UK, which may have influenced maintenance practices.
Findings
- The primary cause of the accident was the separation of a de-icer boot from the left propeller during the takeoff phase.
- The separation was driven by peel stresses generated by the forces acting on the propeller.
- The adhesive bond failed because the mandatory filler material was omitted during the propeller's maintenance.
- The lack of filler created a space where contaminants could accumulate, leading to the eventual failure of the bond.
- At the time of the accident, the existing airworthiness regulations did not require protection for passengers against fragments from piston engines or propellers.