The UK Air Accidents Investigation Branch report into the 30 March 2017 incident reported that 322 litres of fuel leaked from the Bell 412EP helicopter being shipped from Houston to Luxembourg on a Cargolux 747-8F.

During a stop at Glasgow Prestwick, ground crews found fuel had leaked from the main deck through the lower deck to the avionics bay and was “pooling on the apron beneath the aircraft”. Firefighters, who contained the spill, recorded vapour levels which “indicated a high risk of explosion” and fuel flammability limits “potentially in range”.

“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 investigation found.

The Cargolux aircraft suffered extensive fuel contamination and all the system electronics, avionics wire looms and harnesses had to be decontaminated, the report explained. It eventually returned to Luxembourg on 11 April 2017 where major replacements of paneling and elements were carried out.

The report concluded failings in the preparation of the helicopter for transport by not defueling it. “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 defuelled.”