How Data on Successful Flights can Solve Accidents

By John DeLisi

The giant Boeing 777 was coming to the end of a routine flight from Asia and on a nearly perfect descent into Heathrow when the pilot goosed the throttle for a little bit of power on final approach.

That’s when both engines quit.

The British Airways crew worked feverishly to stretch out the airplane’s glide to make it over a busy highway and just over the airport fence. The airplane crashed into a grassy field just 1,000 feet short of runway 27L and did a complete 180-degree turn. Miraculously, there were no fatalities on that January 2008 flight.

The UK Air Accidents Investigation Branch took the lead on the investigation. The NTSB was the accredited representative and Boeing was a technical adviser. Everyone went to the airplane, which is what accident investigators do. But nothing jumped out. There was no smoking gun. The flight data recorder showed a normal flight, up until the engines stopped providing power. The engines checked out mechanically.

It was only after investigators started crunching data did we find out what really happened. Unlike in the United States, European crash investigators have long had access to data on successful prior flights, allowing them to compare the accident flight with many others.

This is what we hope to be able to do with the NTSB’s agreement to share information with the Aviation Safety Information Analysis and Sharing (ASIAS) Executive Board. Under ASIAS, airlines and unions already voluntarily share safety information with FAA to identify trends.

During the 777 investigation, British Airways provided data on about 1,000 previous Beijing-Heathrow flights flown by 777s. The data showed that the accident flight flew at a slightly higher altitude during slightly colder-than-normal temperatures. But what really stuck out was that the accident flight descended largely with its engines in idle – unlike most of the other flights.

Investigators starting focusing on how the engines behaved during long periods of idle in cold temperatures. And they found that an icy slush can build up on the fuel/oil heat exchanger, blocking fuel when the throttles are then increased. That finding led to new procedures and then a new design fix.

This accident probably could not have been solved just by looking at the wreckage and the flight data. Because the icy slush – the evidence — had melted long before investigators could find it. It was solved using data.

This is why the NTSB’s recent agreement is so important. Now we may be able to compare an accident flight with what occurred during similar, successful flights. This data gives us an important new tool for solving accidents that might not be readily solved just by looking at the accident wreckage and flight data.