What happened
On 29 November 2015, a Cessna Citation 560XL, registration SE-RHJ, was performing a commercial passenger flight from Göteborg City Airport, Sweden, to Farnborough Airport, UK. While descending through flight level 200, the crew experienced a sudden loud bang accompanied by aircraft vibrations. The pilots immediately reduced airspeed and disengaged the autopilot. Although the crew could not visually confirm any external damage through the cabin windows, they noted the engine parameters remained within normal limits and the aircraft stayed in trim. As a precaution, the crew configured the aircraft for landing and opted not to utilize thrust reverse. The aircraft landed without further incident, and there were no fatalities or injuries among the two crew members and nine passengers.
The investigation
Upon recovery to a maintenance facility, investigators found that a significant portion of the right engine's upper cowling had detached in flight. This separation caused impact damage to the leading edges of both the vertical and horizontal stabilizers. The investigation focused on the 19 quick-release fasteners used to secure the cowling. While most fasteners remained locked, several were either missing or had been pulled through the cowling material.
Records indicated that the aircraft had been leased to the operator only six days prior and was on its fourth flight following recent maintenance. The investigation established that the engine cowlings had been removed and refitted multiple times recently for troubleshooting and inspections. Two mechanics had installed the cowlings approximately two weeks before the event, with one mechanic signing off the inspection records to confirm the attachments were tightened.
Findings
- The primary cause of the incident was that several fasteners had not been properly secured during maintenance.
- The investigation found that while some fasteners were missing, the remaining fasteners that had pulled through the cowling were still in a locked position.
- There was no evidence that the fasteners were the incorrect size or had suffered mechanical failure during flight.
- The maintenance organization's records showed the cowlings had undergone recent work, including a periodic inspection for wear in the retention holes.