Overview
On Wednesday, 31 January 2001, at approximately 17:00 local time, a Piper PA-31-350 aircraft, registration EC-CJL, was en route from Málaga Airport to Melilla Airport over the Mediterranean Sea, about 25 nautical miles from Melilla. The aircraft was on a commercial air taxi flight with a crew of two and four passengers. The pilot-in-command, age 26, held a commercial pilot license and had 1,175 total flight hours. The aircraft had been refueled to full tanks prior to departure and a pre-flight inspection revealed no anomalies. The flight departed at 16:04 local, climbed to flight level 050, and cruised at 160 knots direct to Melilla.
Incident
While at cruise, the pilot observed through the side cabin window that the upper cowling of the left engine lifted rearward to a near-vertical position and then separated, quickly disappearing from view. The detached cowling impacted the aircraft fuselage, breaking the second window on the left side of the passenger cabin. The impact caused minor injuries to two of the four passengers. The pilot reduced power on the left engine as a precaution, though all engine parameters were normal. Vibration was noted but not considered to affect airworthiness. The crew decided to continue to Melilla. They contacted the control tower, reported their situation, and requested medical assistance. The aircraft landed normally on runway 33.
Injuries and Damage
The two injured passengers were taken by ambulance to a hospital, treated, and released. The aircraft sustained minor damage: the broken window, a dent on the upper fuselage, and impact marks, dents, and erosion diagonally distributed on the left wing between the engine and wingtip—consistent with the cowling's trajectory. The cowling and most of its attachment hardware fell into the sea and were not recovered, except for part of the left side center latch which remained attached to the lower cowling.
Investigation Findings
The lower cowling exhibited fractures and a torn metal flange on the left side; the right side flange was intact but deformed. Paint chips were found on the outer surface behind the propeller cone. The forward lip of the engine nacelle had deformations and fractures. Impact marks were present on the left cylinder head covers and governor housing. The forward baffle was deformed rearward. The propeller cone showed delamination and chips at blade exit holes, and the blades were eroded on the rear side.
Each engine is covered by two fiber cowlings (upper and lower) joined by six internal latches (three per side) operated by external quick-release fasteners, four front quick-release fasteners, and four additional hinge-type safety fasteners installed after production. Each cowling is also attached to the rear nacelle by fifteen quick-release fasteners.
The aircraft had a valid airworthiness certificate until 5 July 2001. The last 100-hour maintenance was performed on 12 December 2000, at which time the aircraft had 6,968 total hours, the left engine 1,146 hours, and the right engine 759 hours. After that maintenance, the aircraft flew 42 hours before the incident.
Probable Cause
The investigation concluded that the detachment of the upper cowling of the left engine probably occurred as a consequence of the failure of one of the fasteners that held it to the lower cowling. This circumstance could have caused an increase in tension on the remaining fasteners and subsequently produced their chain breakage.