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ACCIDENT INVESTIGATORS HAVE DIFFICULT JOB

By the time the pilots of the Falcon 10 see the tree-tops rushing towards them out of the mist shortly after 9.30 a.m., it is too late. The business jet brushes against the topmost branches, tears a 120m long corridor through the woods and is completely ripped apart on impact. For the two pilots and their two passengers no one can help them now.

While the firemen are still grappling with the flames on the site, news of the crash reaches the BFU in Braunschweig at 10.30 a.m. The agency has a standby service available 24 hours a day. For BFU director Peter Schlegel it is obvious what action is required, and two experts from the Federal Bureau set off immediately for Baden-Württemberg to begin their on-site investigations. Most of the staff at the accident investigation bureau are engineers or former pilots. "We need people with flying experience who are experts in aviation technology," says Schlegel, explaining the qualifications of the investigation team.

The search for clues follows a specific predefined plan under which the positions of the aircraft pieces that have broken off are documented to the nearest centimetre with photographs and sketches. Often there are suggestions already at this stage as to the critical sequence of events. Did the crew lose control of their aircraft? At what angle did the business jet hit the ground? Was there an explosion in the air? The distribution of the wreckage gives the first hints of an answer to these questions. In this case, the corridor which the Falcon 10 carved out through the hillside woods provides important information. From the pattern of breakages on the trees the investigators conclude that the aircraft was not banking significantly as it hit the trees, which suggests that the crew had the plane under control until the point of impact.

By contrast, in the Long Island crash of the TWA 800 flight in the summer of 1997 or the bomb attack on the Pan Am jumbo over Lockerbie in Scotland in the winter of 1988, the debris was strewn over a wide area. For the specialists of the US National Transport and Safety Board (NTSB) this was a sure indication that these widebody aircraft had already broken up in the air.

"The investigation of the accident site is only the start. This is followed by intensive detailed work in the laboratory and on the computer," says Peter Schlegel. For the detailed analysis work, the BFU has a hangar of its own at Braunschweig airport, enabling fragments to be lain out for investigation. "Here the analysis is mainly concentrated on particular components or instruments," explains Schlegel. In the case of the crashed Falcon 10, the specialists examine the two horizontal situation indicators (HSIs) closely in the laboratory. The instruments show the position and heading of the aircraft. During the accident they were completely burnt out, but the specialists are able to deduce that the displays were functioning properly and producing correct heading information, since the direction of the display matched the path carved out by the plane as it careered through the wood.

The flight data recorder (FDR) and cockpit voice recorder (CVR) are particularly helpful during the investigation. Today's recording systems pick up conversations, noises and up to 300 flight parameters. With this data a special computer program is able to show the progress of the flight up to the crash. As if in a simulator, the flight attitude, instrument displays and position of the throttle levers or rudders can be displayed on the monitor. When it comes to this kind of analysis, the assistance of the BFU is internationally sought after. After the reunification of Germany the Federal Bureau took over the equipment of the East German investigation bureau and it is also able to analyse recorders of Russian design.

If it was human error that led to the catastrophe, then the CVR will play a key role. The recordings show the unfortunate truth, namely that the crew did not go through their checklists carefully or interpreted their fuel displays incorrectly. The CVR also provides clear evidence in cases of disastrous misunderstandings between the Tower and the pilot. For example, in March 1977 two Boeing 747's collided with each other in thick mist at Tenerife airport. The CVR data showed that the captain of the KLM jumbo that was involved in the crash had misunderstood the air traffic controller's directions and accelerated without being cleared for take-off. His mistake cost 583 people their lives.

Importance evidence as to how the catastrophe came about is often provided by the environment of the flight and the pre-flight preparations. For this reason, the accident investigators also concern themselves with a lot of parameters which at first sight do not seem to have anything to do with the flight. The experts whom the BFU calls on for assistance range from pathologists through to mobile phone experts. Thus forensic scientists investigate whether those involved in the accident were under the influence of alcohol or stimulants. A report from Air Traffic Control reconstructs the flight route with the aid of recorded radar data. If there is any suspicion that cellular phones have interfered with the airborne navigation equipment, then the BFU staff will examine call data for all those on board the aircraft who possessed a mobile phone. The help provided by the meteorologists is particularly important - it is their expertise which explains whether there was a threat of icing at the time of the accident or whether the view was obscured by clouds. For the unfortunate Falcon 10 near Offenburg the report suggested that the accident had happened "because the aircraft had flown into low clouds during the changeover from IFR to VFR on descent."

International co-operation is taken for granted during the analysis. "If the plane was built by a French manufacturer, is registered in Germany and was maintained by a Swiss company, experts from all these countries will work on the accident investigation," says Schlegel. The lead role is always assumed by the authority of the country in which the accident took place.

Should it transpire during the investigation that the accident was caused by a technical defect, the investigators respond by issuing an appropriate warning to all operators of the type concerned. If necessary, this information will result in the type being grounded until all the defects have been rectified. But safety recommendations issued by the BFU are not based solely on the results of the accident investigation. The experts maintain a comprehensive accident database and analyse this data continuously. If it emerges from the analysis that certain aircraft parts have a particularly bad safety record, then the BFU will ask the manufacturer to make improvements. "No manufacturer will willingly admit any defects. Nevertheless, they value our analyses," says Schlegel. Although the Braunschweig investigators adopt the approach of a team of detectives, they have nothing to do with criminal prosecutions. "We're only interested in flight safety, we aren't judges or policemen."

From page 56 of FLUG REVUE 2/2001