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 heard a sudden loud bang accompanied by aircraft vibrations. The crew immediately responded by reducing airspeed and disengaging the autopilot. Although the crew could not visually confirm the source of the noise through the cabin windows, they noted that engine parameters remained normal and the aircraft stayed in trim. To mitigate risk, the crew configured the aircraft for landing and opted not to use thrust reversers. The aircraft landed safely without any 0 injuries to the two crew members or nine passengers.
The investigation
Following the incident, the aircraft was moved to a maintenance facility where investigators found that a large portion of the right engine's upper cowling had detached in flight. The debris had struck the leading edges of both the vertical and horizontal stabilizers, causing visible impact damage.
Technical examination of the engine's attachment system revealed that the upper cowling is secured by 19 quick-release fasteners. While most of these fasteners remained securely locked, investigators found that several were either missing or had been pulled through the cowling material. Specifically, three fasteners were missing from the inboard leading edge, and one was missing from the inboard trailing edge. The remaining empty locking receptacles were found to be in good working order, and the surrounding structure showed no signs of mechanical failure or damage.
Records indicated that the aircraft had been leased to the operator only six days prior and had undergone maintenance approximately five hours of flight time earlier. The maintenance history showed that the cowlings had been recently removed and refitted several times for engine troubleshooting and periodic inspections.
Findings
- The primary cause of the incident was that several engine cowling fasteners had not been properly secured during recent maintenance.
- The detachment of the cowling led to secondary damage to the aircraft's stabilizers due to debris impact.
- The maintenance organization had previously performed inspections on these fasteners, and the installation was signed off as complete by a mechanic.
Safety action
- The maintenance organization has implemented new inspection procedures, requiring an independent mechanic to verify the security of engine cowlings following installation.
- The aircraft manufacturer is reviewing the incident alongside two similar historical occurrences to assess long-term safety options, including the development of instructional videos for maintenance personnel to emphasize the importance of fully securing quick-release fasteners.