Incident
On 11 October 2013, a Britten-Norman BN2A Mk III-2 Trislander, registration G-RLON, was operating a commercial passenger flight from Jersey to Guernsey. After an uneventful flight, ground staff noticed that the cowling on the rear (No 2) engine had become partially detached while passengers were disembarking. The commander, who held an Airline Transport Pilot's Licence and had 14,584 total flying hours (1,008 on type), stated that he had observed nothing unusual during the pre-flight walk-around and that aircraft handling and indications were normal throughout the flight, with no abnormal noise or vibrations.
Investigation
Examination revealed that the cowling consisted of upper and lower fiberglass clamshells. The front right-hand fitting on the lower section had pulled out of the fiberglass and was missing. The resulting loss of structural rigidity allowed movement in the upper cowling, which likely caused two clips securing the upper and lower sections together on the right-hand side to become undone. The degree of movement was sufficient for the upper cowling to make light contact with the propeller blades, leaving rub marks that required subsequent repair.
Repair and Response
The organization conducting repairs noted that cracks in cowlings of aircraft of this age are not unusual, but this was the first instance resulting in loss of a front fastener fitting. The missing fitting prevented determination of the failure mechanism. A fleet check was deemed unnecessary because engine cowling security is already covered by the Daily Inspection. The operator stated that details of this event would be incorporated into their continuation training syllabus.