Air landing systems may be flawed: Crash investigation points to a design fault

A FLAW in the design of the automatic landing system used by most of the world's passenger jets was partly responsible for an airliner crash in which two people died and 45 were injured, according to preliminary findings by accident investigators.

Inquiries indicate that under certain circumstances an aircraft cannot sense when it has landed and will fail to activate the automatic brakes immediately.

This follows a crash in September in which an Airbus Industrie A320, one of the world's most advanced airliners, failed to stop on the runway at Warsaw airport, hit an embankment and burst into flames.

Early investigations into the incident have identified a previously unknown problem in the design of the automatic braking mechanism. The system is used on many airliners, and not just those manufactured by Airbus.

A heavy rainstorm and the condition of the runway are also believed to have played an important role in the accident.

If the initial findings are confirmed in the final report, modifications - costing millions of pounds - may have to be made. Airbus denies a design fault caused the crash.

This comes at a time when pilots have criticised some modern aeroplanes for relying too heavily on computers and automatic flight systems.

On 14 September the Lufthansa Airbus with 70 passengers and crew, flying from Frankfurt, landed in heavy rain at Okecie airport in Warsaw. It appeared to land safely but the brakes were not activated until nine seconds after touchdown, according to a source involved in the investigation.

Unable to stop, the aircraft hit an earth bank. The left wing and engine burst into flames and snapped off. As the broken fuselage settled into the soft ground, the fire spread, engulfing the top half of the plane. The co-pilot and a German passenger were killed.

Normally, when an aircraft lands, its weight triggers sensors or 'squat switches' on the undercarriage which command the aircraft's computers to activate the thrust reversers and ground spoilers. This type of braking design is used on most passenger aircraft.

However a source involved in the inquiry, which is being run by the Polish air accident investigators and assisted by the French and German authorities, has revealed that the braking mechanism failed to work until the aircraft had travelled along the ground for about 700m. It is then believed to have aquaplaned on water on the runway.

Investigators, from the preliminary work, believe the braking failure was linked to an unexpectedly strong tail wind and unusually large amounts of surface water.

At first only one wheel is understood to have touched the runway - a built-in safety device means both most be on the ground before the brakes are activated. The wet and windy conditions then caused the undercarriage to 'float' along the runway and did not create enough pressure or wheel speed to activate the sensors.

This version of events is supported by witness accounts. Marcin Bronikowski, a passenger, said: 'There had been hand-clapping after the landing. But instead of the plane losing speed, it started to gain speed on the runway.

'After that, the runway ended and the plane jumped up into the air. I think it broke in half and started to burn. A wing fell off and panic broke out.'

The aquaplaning caused the aircraft's anti-skid system to fail because the jet's wheels were not spinning fast enough to activate it.

Another vital element may have been the condition of Okecie airport, which is known to have had problems with drainage. In addition the Warsaw control tower cannot provide continuous measurements of surface wind speed, but relies on three-minute updates.

Airbus and Lufthansa have refused to comment on the cause of the accident until the inquiry report is published. However, Robert Alizart, vice- president of corporate communication at Airbus, confirmed that the brakes failed to work until nine seconds after landing.

He said: 'There is no indication of any design problem. This incident was unique - sometimes it's difficult to guard against certain situations. The A320 is one of the safest aircraft in the world.'

A Lufthansa spokesman said: 'If there is any chance this accident could be repeated we will demand immediate action - if this means a change in the design then we will insist on it. The whole issue is of major concern to us.

'There is no indication of pilot error,' he added.

There are 415 A320s in service. British Airways has 10.

The crash in Warsaw was the fourth fatal accident involving the 150-seater airliner since its introduction in 1988. Eighty- seven people died in January last year near Strasbourg. In 1988 at Mulhouse, France, three people died at an air show, and at Bangalore in India, 92 were killed in 1990. In the last two cases, pilot error was blamed.

(Photograph omitted)