AIR CRASH REPORT

Heathrow Airport Air Crash Accident Report

An interim accident report into the British Airways Boeing 777 crash-landing at London Heathrow Airport last month says the accident was not caused by faults with the aircraft's engines.

The Air Accident Investigation Branch (AAIB) said their investigations into the damaged aircraft and the jet's black box flight data recorders had shown there was nothing wrong with major systems on the aircraft.

In an initial report released the day after the accident on 17th January, the AAIB said the 777's two engines "did not respond" to requests from the crew for more power as the aircraft was on final approach.

After completing further investigations, however, the investigators now say they have ruled out the accident being caused by a mechanical problem with the engines.

"Examination of the engines indicated no evidence of a mechanical defect [with the engines] or ingestion of birds or ice," the report said.

Investigators had tested the electric and electronic controls for the engine and fuel systems, and found them to be working well.

The report said: "The autopilot and the auto-throttle systems behaved correctly and the engine control systems were providing the correct commands prior to, during and after the reduction in thrust".

Despite ruling out the possibility of mechanical problems, the AAIB's interim report did not give a specific cause of the accident.

Boeing 777 Fuel Flow To Be Investigated

However, the AAIB said "a comprehensive examination and analysis is to be conducted of the entire aircraft and engine fuel system, including the modelling of fuel flows and taking account of the environmental and aerodynamic effects".

Industry experts believe this shows the AAIB thinks a potential cause of the accident was a partial interruption with the aircraft's fuel flow system.

Indeed, the AAIB report stated: "Detailed examination of both the left and right engine high pressure fuel pumps revealed signs of abnormal cavitation [air bubbles] on the pressure-side bearings and the outlet ports. This could be indicative of either a restriction in the fuel supply to the pumps or excessive aeration of the fuel".

The AAIB did not say this was a cause of the accident, but that it would be carrying out investigations to compare the damage to the fuel pumps with the aircraft's flight data.

The report added that "insignificant" quantities of water had been found in the fuel, and several items of debris in the fuel tanks themselves. It said investigators would be examining this to see if had any relevance to the accident.

Heathrow Air Crash Safety Recommendation

The AAIB did make one safety recommendation in light of its investigations.

Operating procedures for the 777 show that these valves should be cut off first, either manually or automatically, before the fire handle - which is responsible for working the aircraft's fire extinguisher.

Investigators found that, due to the pressure of the situation, the aircraft's crew had failed to cut off one of the fuel valves, which are designed to stop the fuel supply immediately if an accident or engine fire occurs.

The AAIB said this lead to a loss of fuel from the aircraft. The report noted that while this "was not causal to the accident", it "could have had serious consequences in the event of a fire during the evacuation".

The AAIB recommended that Boeing should instruct all airline operators of the Boeing 777 to ensure their crews are fully briefed to cut the fuel valves before using the fire handle.

The Boeing 777 involved in the dramatic incident was on arrival from Beijing when it crash-landed short of Heathrow's Runway 27L onto the threshold, with extensive damage being inflicted on the aircraft as it skidded across the grass to the runway. All 136 passengers and 16 crew were safely evacuated from the aircraft with only several passengers receiving minor injuries.

Source - Airport International's Aviation Correspondent