Failure to defuel a helicopter before it was shipped on board a Cargolux Boeing 747-8F resulted in a serious leak of more than 250kg of fuel, presenting a substantial risk of explosion and badly contaminating the jet’s interior.

The Bell 412EP helicopter, destined to be shipped to Germany, was being transported on the 747 from Houston to Luxembourg on 30 March last year, with an intermediate stop in Glasgow Prestwick.

Ground crews at Prestwick discovered a fuel leak from the helicopter and emergency personnel, summoned to the scene, found fuel pooling beneath the jet. It had leaked from the main deck, through the lower deck and avionics bay.

Firefighters subsequently stated that measured fuel vapour levels “indicated a high risk of explosion” and fuel flammability limits were “potentially in range”, says the UK Air Accidents Investigation Branch.

Some 255kg of fuel – equating to 322 litres – had escaped from the helicopter during the transatlantic flight.

Before being shipped, the inquiry says, the helicopter spent two months in storage in Houston, without problems, and there was no evidence of a fuel system issue.

Investigators point out that the helicopter’s structure was shrink-wrapped for transport. The probe suggests the manner in which its fuel vents were wrapped could have resulted in a siphon effect or a temporary deformation of the fuel cells as cabin pressure changed – causing fuel to be ejected from the forward right-hand vent, which had been left exposed.

The helicopter, serial number 36414, had been bought by Germany’s Agrarflug Helilift from Bristow US. But the inquiry says that, critically, the opportunity to check that the helicopter had been defuelled prior to transport was not taken.

Investigators state that the buyer assumed the seller would disassemble and prepare the helicopter for shipping in accordance with guidelines from the helicopter’s manufacturer – which recommended defuelling. The seller considered that all transportation matters were the buyer’s responsibility, although it was aware that the helicopter was being shipped as air cargo.

“Neither the seller’s staff undertaking the disassembly, nor the buyer’s representatives who were subsequently in attendance, identified the fact that a substantial amount of fuel remained on board the helicopter prior to it being packaged,” says the inquiry, which also points out that the shrink-wrap packaging procedure involved using an open-flame torch.

It had been loaded onto another Cargolux flight, three days before the Prestwick incident, but the loading supervisor noticed a small fuel leak. The helicopter was offloaded and returned to the warehouse.

Video surveillance shows that, the following day, the helicopter was subjected to a 30min inspection at a cargo facility, conducted by a mechanic, shipping agent and ground-handling agent.

But no walk-around was performed and the mechanic did not use any tools to remove the shrink-wrap on the helicopter, instead just inserting some absorbent pads and informing relevant parties that the leak had originated from residual fuel in the lines.

As a result, Agrarflug – without direct verification – issued a certificate stating the helicopter had been purged of all fluids and was not considered dangerous goods.

There was a “dilution of responsibility” among the various individuals and organisations charged with shipping the helicopter, says the inquiry.

“No single organisation or individual was able to assure that the shipping documentation reflected the actual condition of the helicopter,” it adds.

The five-year old 747-8F (LX-VCF) suffered extensive fuel contamination. Internal floor, ceiling and sidewall panels were lifted and damaged insulation blankets were removed, while aircraft electronics and avionics wiring required decontamination.

It was ferried back to its home base on 11 April, nearly two weeks after the event, where it underwent further measures to restore it to full airworthiness – including replacement of insulation blankets, panels, and parts of the cargo-loading system. The aircraft was also inspected, cleaned and treated with corrosion-inhibiting fluid.

Source: Cirium Dashboard