What happened
On 30 May 2008, a PILATUS PC6-B2H4 Turbo-Porter, registration EC-JXH, departed from Lillo Aerodrome for a scheduled parachute drop operation. The aircraft was carrying a pilot and ten skydivers, including several instructors and students performing tandem jumps.
While climbing at approximately 14,000 ft, the pilot initiated a left turn to align with the jump heading. During this maneuver, the aircraft encountered intense negative acceleration and severe turbulence. The structural integrity of the aircraft failed as the left wing fractured and detached from the fuselage. Simultaneously, components of the horizontal stabilizer also broke away.
The loss of the wing caused the aircraft to invert and enter a violent clockwise spin. The centrifugal forces and the aircraft's rotation caused the left-side swing doors to open, ejecting eight of the skydivers into the air. One additional passenger was ejected through the shattered windshield. Nine of the occupants managed to deploy their parachutes and land safely. However, the pilot and one passenger remained trapped in the cabin. The aircraft impacted a field 4.5 km north of the aerodrome and caught fire, resulting in 2 fatalities and 4 injuries.
The investigation
The CIAIAC investigation focused on the structural failure of the wing and tail assembly. Laboratory analysis conducted by the National Institute for Aerospace Technology (INTA) examined the fractures in the wing spar, the horizontal stabilizer, and the wing struts.
Investigators performed a macroscopic and microfractographic analysis of the wreckage. The study of the left wing spar and the horizontal stabilizer components revealed that the fractures were ductile in nature and were the result of static overload. The investigation ruled out progressive fatigue, material failure, or stress corrosion as causes. The findings confirmed that the structural loads applied to the aircraft exceeded the design limits specified for its maneuvering envelope.
Findings
- The aircraft entered an area of intense turbulence within a storm cell while performing a left turn.
- The combination of aerodynamic and inertial loads during the maneuver caused the left wing and parts of the horizontal stabilizer to exceed their structural strength.
- The aircraft's operator and jump supervisors were unaware of the severe storm cell located to the north of the aerodrome, as they were primarily focused on a different storm approaching from the south.
- Localized weather information (METAR/TAFOR) was unavailable for the specific site, as the nearest official reports were from a distant aerodrome.