B748, Prestwick UK, 2017

B748, Prestwick UK, 2017


On 30 March 2017, a significant amount of fuel was found to be escaping from a Boeing 747-8F as soon as it arrived on stand after landing at Prestwick and the fire service attended to contain the spill and manage the associated risk of fire and explosion. The Investigation found that the fuel had come from a Bell 412 helicopter that was part of the main deck cargo and that this had been certified as drained of fuel when it was not. The shipper s procedures, in particular in respect of their agents in the matter, were found to be deficient.

Event Details
Event Type
Flight Conditions
Not Recorded
Flight Details
Type of Flight
Public Transport (Cargo)
Intended Destination
Take-off Commenced
Flight Airborne
Flight Completed
Phase of Flight
Location - Airport
Procedural non compliance
Cargo Aircraft Loading, Dangerous Goods
Damage or injury
Aircraft damage
Non-aircraft damage
Non-occupant Casualties
Number of Non-occupant Fatalities
Number of Occupant Fatalities
Off Airport Landing
Causal Factor Group(s)
Aircraft Operation
Safety Recommendation(s)
Aircraft Operation
Investigation Type


On 30 March 2017, a Boeing 747-8F (LX-VCF) being operated by Cargolux on a scheduled cargo flight from Houston to Luxembourg via Prestwick as CV7754 was found to be leaking significant quantities of aviation fuel from the lower fuselage as soon as it reached its allocated parking position at Prestwick in normal daylight visibility. The source of the fuel was found to be a helicopter on board as part of the main deck cargo. The Airport RFFS were called and contained the fuel spill and managed the associated risk of fire and explosion.


A Field Investigation was carried out by the UK AAIB. The 52 year-old Captain of the flight was noted to have accumulated 12,900 hours of which 9,200 hours were on type. It was found that the first hint that anything was amiss was a smell of fuel detected by the flight crew as they shut down the engines.

When the ground operations agent entered the aircraft via the main deck door to commence unloading operations, he also detected a strong smell of aviation fuel and reported having heard the sound of running liquid. He identified the source of the fuel as a Bell 412EP helicopter which was part of the main deck cargo and discovered that fuel appeared to be leaking from a vent on the forward right-hand side of the helicopter. The situation was reported to the flight crew and the Airport Authority and the Airport RFFS were notified. The Airport Emergency Response Plan was activated and the aircraft was fully shut down and the crew escape hatch and upper deck service door were opened to help ventilate the aircraft.

Upon arrival at the aircraft the RFFS established that fuel from the helicopter was coming out of a drain hole at the bottom of the fuselage close to the left body landing gear, having leaked through the main deck, lower deck and avionics bay. They subsequently advised that “the measured fuel vapour levels indicated a high risk of explosion and that the fuel flammability limits were potentially in range”. It was also observed that “the presence of fuel in proximity to potentially hot wheel brakes (had) created a substantial risk of fire”. Overall it was considered that “the escape of fuel from the helicopter represented a substantial hazard to the safety of the aircraft, the flight crew and those on the ground at Prestwick Airport”. After the aircraft had been made safe, all cargo, including the helicopter, was offloaded manually.

When the helicopter was examined prior to the removal of the shrink wrapping in which it had been shipped, this wrapping was found to have been breached at the forward right hand fuel vent and fuel had evidently leaked from there. Some fuel was also present in the wells of the pallet on which it had been loaded and some of the straps securing it to that pallet were “soaked with fuel”. There was no sign of fuel leaking out of breaches anywhere else in the shrink wrapping.

When the helicopter cabin was opened, it was noted that the helicopter’s main battery with a ‘Class 8 (corrosive) hazard’ label affixed was found to be installed in its normal position although disconnected. A fire extinguisher was also found secured to a floor stowage.

Fuel draining from the lower fuselage of the aircraft after arrival at Prestwick. [Reproduced from the Official Report]

A comparison of the declared weight of the consignment as shipped and the weight of it after fuel had leaked showed a difference of 255 kg. When the helicopter was electrically powered-up, the total quantity of fuel on board was indicated as 1,440 lb and it subsequently took a 467 litre uplift - equivalent to approximately 369 kg - to reach a full tanks indication. No fuel leaked from the helicopter after this refuelling had taken place.

The interior of the aircraft main deck had been extensively contaminated. Once the fuel vapours had dispersed, internal floor and ceiling panels and sidewall liners were lifted and all the contaminated insulation blankets removed. All the aircraft’s electronics, avionics wire looms and harnesses also needed to be decontaminated. After a ferry flight to Luxembourg two weeks after the event, a number of additional actions were required to return the aircraft to a fully airworthy condition, including extensive inspections, cleaning and the application of corrosion-inhibiting fluid. All the insulation blankets and lower deck ceiling liner panels and some components of the cargo loading system also had to be replaced.

It was established that in December 2016, the helicopter had been sold by Bristow US, who were based in Louisiana, to a new German owner, Agrarflug Helilift. The process of arranging the shipment which Cargolux eventually carried was found to have involved a number of different agencies and individuals dealing with various aspects of the sale, preparation and transport of the helicopter to Houston Airport for loading. Apart from the seller and the buyer, these included a sales agent representing the buyer in the US and his assistants and “freight forwarding work” carried out by three organisations. A New Zealand-based routing agent was also appointed to oversee the export requirements and transportation of the helicopter to Germany and it subsequently sub-contracted this work to a US-based cargo logistics company to act on their behalf in the US and this sub-contractor then appointed a US-based shipping agent to prepare the Air Waybill and monitor progress.

The helicopter had been partly disassembled by the seller’s staff at their facility and loose items were crated. The fuselage was then shrink-wrapped in heavy duty plastic by a specialist company contracted by the sales agent who subsequently noted that “an open flame torch was used to shrink the plastic wrap and that they would not have wrapped the helicopter if they had known it was fuelled”. It had been intended that the buyer’s sales agent would oversee the disassembly of the helicopter and its preparation for transport by the seller but he was unable to attend and arranged for two assistants to attend instead. However, only one was present when the helicopter fuselage was shrink-wrapped and it had already been disassembled prior to his arrival. The second assistant was present to observe the shipment being loaded onto the vehicles of a road haulage company which had been engaged to move the shipment from the seller’s facility to Houston Airport.

The Cargolux Sales Department booked-in the shipment of 9 loose crates and the helicopter fuselage on 23 January 2017 based on a quotation they had given five months earlier. The shipping agent “explicitly indicated in writing that all fuels and batteries had been removed from the helicopter and that the shipment was non-hazardous” and issued an Air Waybill for the shipment the following day. The shipment arrived at the Cargolux facility at Houston Airport on 26 January 2017 and was “accepted for travel by the Dangerous Goods Manager from the Operator’s contracted Ground Handling Agent (GHA)”. It was then not released for export by US government agencies until 21 March 2017. After loading onto a Cargolux aircraft on 27 March 2017, the Operator’s loading supervisor noticed a small fuel leak from the helicopter and so it was offloaded and the Operator’s sales asked the shipping agent to arrange for an inspection of the helicopter. This was carried out the following day by a mechanic in the presence of representatives from the shipping agent and the Operator’s sales department. A further inspection, again with shipping agent present and this time escorted by a GHA employee, was carried out later the same day. Review of CCTV footage showed that this second inspection took approximately 30 minutes. It was noted that “no walkround was conducted, the mechanic appeared to focus his attention on the lower surface of the helicopter and did not use any tools or remove the shrink-wrap to facilitate inspection of the helicopter”. He “used a cleaning spray to clean parts of the exterior surface, inserted absorbent pads between the shrink-wrap and the helicopter skin and applied some white tape over the shrink-wrap” and the airline and the other agencies involved including the cargo logistics company were then informed “the fuel leak had originated from residual fuel in the fuel lines and had been capped off”.

After the shipping agent had provided Cargolux with a revised Air Waybill and Air Cargo Manifest and “Purge Certificate” indicating that the helicopter was free from fuel, the shipment was accepted and was loaded onto flight CV7754 as being exempt from the regulations applicable to the carriage of Dangerous Goods by air. The loading supervisor responsible for the flight reported having checked the helicopter prior to, during and after loading and having seen “no evidence of a fuel leak or spill”.

A considerable number of administrative irregularities and incorrect declarations were discovered in respect of the shipment of the helicopter as air freight and it appeared that there had been confusion between the seller and buyer of the helicopter as to who was responsible for disassembly of the helicopter and its preparation for carriage by air in accordance with applicable regulations. At the end of this process, the Dangerous Goods NOTOC (Notification to Captain) presented to the Captain of the aircraft made no mention of the helicopter.

The applicable requirements of ICAO Annex 18 include that dangerous goods must be carried in accordance with ICAO document 9284 ‘Technical instructions for the safe transport of dangerous goods by air’. The helicopter was Class 9 Dangerous Goods and in the category ‘UN3166 Vehicle, flammable-liquid powered’ and had required special preparation, packaging and labelling to identify it as dangerous goods. However, conditional exemption from the Dangerous Goods Regulations (DGR) was possible under Special Provision A70 which would have allowed the helicopter to be transported by air without being declared as dangerous goods providing batteries and other dangerous goods were removed and that the fuel tank and fuel system had been flushed and purged of all fuel and fuel vapours. The helicopter was presented to Cargolux for carriage under an A70 exemption which was invalid. It was noted that the responsibility for complying with the Dangerous Goods Regulations lies with “the shipper”. It was stated by Bristow US that “under the terms of the sales agreement, the buyer had complete responsibility for inspecting and transporting the helicopter”.

The FAA were notified of the event and undertook its own investigation into the issues relating to undeclared and leaking dangerous goods. This involved interviews with many of the individuals and organisations who had been involved but although details from these interviews were shared with the AAIB, not all the parties involved “engaged directly with the AAIB” who as a result were therefore unable to fully explore some of the issues.

A Review of the Evidence

A number of aspects of the event were examined further and various positions established, including but not limited to the following:

  • Notwithstanding the issue of where the contractual commitment for preparation and de-fuelling of the helicopter lay, the disassembly of the helicopter and preparations for its transport took place at the seller’s facility and were conducted by its staff, despite a substantial amount of fuel remaining on the helicopter. The buyer assumed that the helicopter would be prepared in accordance with guidance published by the helicopter manufacturer, which recommends de-fuelling as part of the preparations for transportation. 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 onboard the helicopter prior to it being packaged and transported.
  • The Shipper’s Export Declaration for the helicopter indicated that no hazardous materials were being exported and formed the basis for other transportation documentation. However, it did not accurately reflect the presence of fuel on board the helicopter, nor the battery and fire extinguisher within the helicopter cabin, which also required identification as dangerous goods. The documentation prepared in connection with carriage by air indicated the helicopter was being shipped as unrestricted cargo under the provisions of DGR Special Provision A70 which did not reflect the actual condition of the helicopter and precluded both Cargolux and its flight crew from awareness of the actual hazard it represented. As the designated shipper named on the Air Waybill, the legal contract of carriage by air was between the cargo logistics company and the operator. However, the cargo logistics company further delegated responsibility for production of the shipping documentation to the shipping agent and this documentation was not in compliance with the DGR nor did it correspond to the actual state of the helicopter. The dilution of responsibility among the various individuals and organisations involved in the shipping of the helicopter meant that no single organisation or individual was able to assure that the shipping documentation was correct. Whilst there was insufficient evidence to support a formal Safety Recommendation on this matter, findings of the Investigation were with the IATA Dangerous Goods Board which in conjunction with ICAO publishes the DGR.
  • The small fuel leak observed when the helicopter was first loaded onto an aircraft at Houston provided a missed opportunity to detect the presence of Dangerous Goods. No attempt was made to determine the actual fuel state of the helicopter during the subsequent inspections and a series of incorrect documents followed as a result.
  • The way in which the fuel had escaped during flight was considered. Since the battery was disconnected, none of the fuel pumps could have operated during the flight and it was noted that possible ways for fuel to escape would have been via the fuel vent lines, the sump drain valves, the de-fuelling valves or a loose connection in a fuel system interconnect line. It was considered that the most likely origin of the leak was the forward right-hand fuel vent tube which had been found protruding from the shrink wrap whereas the forward left-hand vent was completely sealed. Given the nature of the fuel system, it was considered that the sealed forward left vent tube “may have prevented the pressure within the fuel tank’s four forward fuel cells from equalising in response to aircraft cabin pressure changes during the descent into Prestwick […] (and) induced a siphon-like effect, or caused the flexible fuel cells to temporarily deform as the aircraft’s cabin pressure equalised during the descent”, either of which would have caused fuel to be ejected via the open forward right-hand vent tube.
  • The precise fuel state of the helicopter prior to its shipment by air was unknown but it was considered that the 255 kg difference between the declared and post-shipment weight of the helicopter fuselage pallet represented the weight of fuel which had escaped from the helicopter during the flight, a weight would be equivalent to approximately 322 litres. On this basis, the fuel state of the helicopter prior to transportation was calculated to have been approximately 1,442 litres which would have meant that all the lower fuel cells would have been full. It was noted that the combined capacity of the lower forward and lower middle tanks, served by the forward vent lines, is approximately 304.7 litres, broadly equivalent to the quantity of fuel calculated to have escaped during the flight.

The formal statement of the Conclusions of the Investigation was as follows: 

Regardless of the exact mechanism by which the fuel escaped from the helicopter, the IATA Dangerous Goods Regulations (DGR) exist to prevent the transportation of hazardous cargo representing a hazard to the safety of an aircraft. Adequate steps were not taken to correctly prepare the helicopter for transport and this situation was not identified prior to it being offered for transportation by air. The Investigation identified that the dilution of responsibility among the various individuals and agencies involved meant that no one agency or individual could assure that the shipping documentation reflected the actual condition of the helicopter and was in compliance with the DGR. An inspection of the helicopter prior to travel was superficial in nature and, although no attempt was made to verify the actual fuel state of the helicopter, incorrectly concluded that the helicopter had been de-fuelled.

This resulted in the helicopter shipment being identified as unrestricted cargo, despite containing non-declared dangerous goods. The fuel hazard was not identified to the Operator or the Commander of the flight on which the helicopter travelled, and they were therefore unaware of the risk it posed. The escape of fuel from the helicopter during the flight represented a substantial hazard to the safety of the aircraft, the flight crew and those on the ground at Prestwick Airport. The containment actions taken by the RFFS at Prestwick Airport substantially reduced the possibility of a more adverse outcome.

One Safety Recommendation was made as a result of the Investigation as follows:

  • that Bristow US LLC review their procedures relating to the preparation of helicopters for air transportation to ensure that they are de-fuelled. [2018-011]

Safety Action taken by Cargolux is known to have included a number of revisions to its operating procedures and a recommendation to its contracted Ground Handling Agent that steps should be taken to raise awareness among its staff of the possibility of dangerous goods in general cargo and to improve methods of detecting undeclared dangerous goods.

The Final Report of the Investigation was initially published on 12 July 2018 and subsequently slightly amended and re-issued on 15 August 2018.

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