What happened
On 30 March 2017, a Boeing 747-8R7F, registration LX-VCF, arrived at Prestwick International Airport from Houston, Texas, as part of a scheduled cargo flight. During the engine shutdown process, the flight crew detected a strong odor of aviation fuel. Upon inspection by ground personnel, it was discovered that a Bell 412EP helicopter, secured on the main deck, was leaking fuel. The liquid had migrated through the aircraft's main and lower decks, eventually exiting the fuselage and pooling on the airport apron.
The leak caused extensive fuel contamination of the aircraft's interior, including wiring, avionics, and insulation blankets. Due to the high concentration of fuel vapors, the Airport Rescue and Fire Fighting Services (RFFS) identified a significant risk of fire and explosion, leading to the evacuation and quarantine of the aircraft.
The investigation
The AAIB investigation established that the helicopter had not been properly prepared for air transport. Although documentation and a 'Purge Certificate' suggested the aircraft was empty of hazardous materials, the helicopter still contained a substantial amount of fuel. The investigation found that the helicopter's forward right-hand fuel vent had been left exposed by the shrink-wrap, while the left-hand vent was sealed. This discrepancy, combined with changes in cabin pressure during descent, likely induced a siphon-like effect that ejected fuel from the exposed vent.
Investigators also examined the logistics chain, noting that responsibilities were divided among several agencies, including the seller, buyer, and various freight forwarders. A mechanic's inspection in Houston had previously noted a small leak but incorrectly concluded it was merely residual fuel in the lines, rather than a significant quantity remaining in the tanks.
Findings
- The helicopter was not defuelled prior to transportation, contrary to manufacturer guidance and shipping declarations.
- The helicopter was shipped as non-hazardous cargo despite containing undeclured dangerous goods.
- The shrink-wrapping process created a pressure imbalance between the sealed and exposed vents.
- A lack of clear, single-point responsibility among the various shipping agents led to inaccurate documentation and a failure to identify the fuel hazard.