Air accident investigators believe a modification to a bar unit on a passenger jet may have been responsible for a fire in electrical wiring which forced the crew to make an emergency landing.
A preliminary report into the serious incident on board a Virgin Atlantic Airbus A340 en route from Heathrow to Chicago last month was published today. There were 143 passengers and 13 crew on board when the rescue services responded to a full-scale emergency on January 11th last.
The aircraft made an emergency landing at Shannon airport after the crew reported a small fire in the bottom of a waste bin storage compartment of the bar unit in the first class section of the plane. Virgin Atlantic said at the time there had been no fire on board.
The fire was located in a hole in the floor of the compartment, the report by the Air Accident Investigation Unit (AAIU) said today.
Cabin crew noted that a damaged electric cable loom appeared to be sticking out of the hole and there was ‘arcing’ in the hole – a phenomenon that can result from an electrical fault.
The cockpit crew turned off power circuits, but the fire and arcing persisted, the report said.
“The captain declared an emergency and diverted to Shannon, where the aircraft landed safety some 30 minutes later.”
As the plane diverted, five 1kg fire extinguishers were used by the cabin crew in efforts to stop the fire. These subdued the flames but the arcing persisted. After each application, the fire restarted after about five minutes.
The flames were not large but were described by witnesses as “licks of flame”.
After landing, the airport fire service tackled the fire with a 5kg extinguisher, but a glow continued to be observed at the bottom of the hole, the accident report said.
Fire chiefs discussed the situation with the crew and the aircraft was powered down. The glow then disappeared and no further arcing was observed.
Investigators found the cable loom in the bottom of the waste bin compartment had been “completely severed” and bore “strong evidence of burning/arcing”.
The wiring loom in question consisted of 10 wires in a protective sheath and was used to provide power and dimming circuits for “mood” lighting in the bar unit counter top.
It appeared the lower edge of the metal waste bin made contact with the wiring loom.
Investigators said there was “no evidence” of a protective metal cover and rails that should have been present to keep the bin above the wiring loom.
“Initial inspection indicated the possibility that they were never fitted,” the report said.
The bar unit itself was a modification, specific to Virgin aircraft. It was installed three years ago, seven years after the aircraft was manufactured.
Investigators said a fleet inspection of Virgin’s A340-300 and A340-600 aircraft found that a number of them also had problems relating to missing covers, rail screws and cable routing in this area.
Damage to the same wiring loom was found on one other aircaft.
The AAIU report said a similar bar is installed in Virgin’s Boeing 747-400 fleet, but the same potential for cable damage did not arise in that aircraft.
“While the cause of the wiring damage to this aircraft has been determined, significant other issues are being examined by the investigation.
These include the difficulties faced by the crew in isolating the damaged circuits, the emergency checklist, the design of the modification and the standards relating to such modifications,” the report stated.
The investigation is ongoing and a final report will be published by investigators in due course.
Virgin Atlantic said it immediately launched an investigation and a thorough inspection of its aircraft in full co-operation with the AAIU after the incident.
“A few minor issues were found and were immediately rectified,” said a spokesman.
“The installation of the bar was carried out in accordance with all relevant regulations. Virgin Atlantic continues to assist the AAIU in their investigation and looks forward to the full report with interest.”
Additional reporting: PA