Summary
On 29 November 2015, a Cessna 560XL Citation, registration SE-RHJ, experienced an in-flight loss of its right engine upper cowling during descent into Farnborough Airport, Hampshire. The aircraft, operated as a commercial air transport passenger flight, had departed Göteborg City Airport, Sweden. The crew of two and nine passengers were uninjured, and the aircraft landed uneventfully. The cowling detachment caused impact damage to the leading edges of the vertical and horizontal stabilisers.
History of the Flight
While descending through approximately FL200, the crew heard a sudden bang and felt vibrations. They reduced speed and disengaged the autopilot. Engine parameters remained normal, and the aircraft stayed in trim. Concerned about possible damage to the rear of the aircraft, the crew checked through cabin windows but saw nothing unusual. They configured for landing and decided not to use thrust reversers. The landing was uneventful.
Investigation
Post-flight inspection revealed that most of the right engine upper cowling was missing. Damage to the leading edges of the vertical and horizontal stabilisers was consistent with debris impact. The upper cowling was attached to the engine by 19 quick-release fasteners—10 on the leading edge and 9 on the trailing edge. These fasteners lock by turning them clockwise about a quarter turn, moving a cross pin up a cam into a locking detent. A spring within the fastener governs preload and prevents loosening from vibration.
Examination of the remaining cowling remnants showed they had been pulled from the fasteners. All but four of the fasteners remained securely locked. Three fasteners were missing from the inboard leading edge, and one from the inboard trailing edge. The empty locking receptacles were confirmed serviceable using a representative fastener, and the surrounding structure showed no damage.
Aircraft History
The aircraft had been leased to the operator six days before the incident and was on its fourth flight since maintenance. Total flight time since maintenance was approximately five hours. The engine cowlings had been removed and refitted several times during engine troubleshooting. Records indicated that the fasteners had been removed as part of a periodic inspection for retention hole wear; no anomalies were found, and the original fasteners were refitted.
Two mechanics installed the cowlings about two weeks before the event. They reported no difficulty during installation, and one mechanic signed post-maintenance inspection records confirming the cowlings were closed and attachments tightened. The cowlings were not disturbed after the aircraft left the maintenance organisation.
Previous Occurrences
Two similar events involving Cessna 560XL aircraft were recorded. In April 2008, SE-RCL lost a left engine cowling during approach to Geneva, attributed to unsecured fasteners. In June 2008, G-OROO lost approximately 75% of its left engine upper cowling after maintenance, also due to unsecured fasteners. In both cases, the maintenance organisations introduced changes to prevent recurrence. The manufacturer reviewed service records and found no evidence of emergent trends for upper cowling loss on the 560XL series.
Conclusion
The investigation concluded that the cowling probably detached because a number of fasteners had not been securely fastened during maintenance. It was unlikely that the fasteners were the wrong size or failed in flight.
Safety Action
The maintenance organisation changed its inspection procedures to require an independent mechanic to verify the security of engine cowlings after installation. The manufacturer highlighted the three events to its Continued Operational Safety group to assess possible options, including a proposed video for maintenance agencies emphasising the importance of ensuring quick-release fasteners are secure.