Lufthansa Flight 2904

Lufthansa Flight 2904

Wreckage of Flight 2904 on 15 September 1993
Accident summary
Date 14 September 1993
Summary Overshot runway, pilot error
Site Warsaw, Poland
Passengers 64
Crew 6
Fatalities 2
Injuries (non-fatal) 68
Survivors 68
Aircraft type Airbus A320-211
Operator Lufthansa
Registration D-AIPN

Lufthansa Flight 2904 was an Airbus A320-200 which overran the runway at Okęcie International Airport on 14 September 1993. It was a flight from Frankfurt, Germany to Warsaw, Poland.

Incident description

Airbus A320
Illustration of time elapsed between touchdown of the first main strut, the second, and engagement of brakes.

Lufthansa Flight 2904 was cleared to land at Okęcie International Airport Runway 11 and was informed of the existence of wind shear on the approach. To compensate for the crosswind, the pilots attempted to touch down with the aircraft banked slightly to the right. Additionally they landed with a speed about 20 knots (37 km/h) faster than usual. According to the manual, this was the correct procedure for the reported weather conditions, but the weather report was not up-to-date. At the moment of touchdown, the assumed crosswind turned out to be a tailwind. Due to the tailwind of approximately 20 knots (37 km/h) and the increased speed, the airplane hit the ground at approximately 170 knots (310 km/h) and far beyond the normal touch down point. The aircraft's right gear touched down 770 m from the runway 11 threshold. The left gear touched down 9 seconds later, 1525 m from the threshold. Only when the left gear touched the runway did the ground spoilers and engine thrust reversers start to deploy, these systems depending on oleo strut (shock absorber) compression. The wheel brakes, triggered by wheel rotation being equal to or greater than 72 knots (133 km/h), began to operate about 4 seconds later.

The remaining length of the runway (left from the moment when braking systems had begun to work) was too short to enable the aircraft to stop on the remaining runway. Seeing the approaching end of the runway and the obstacle behind it, the pilot steered the aircraft off the runway to the right. The aircraft departed the runway at a speed of 72 knots (133 km/h) and rolled 90 m before it hit the embankment and an LLZ aerial with the left wing. A fire started in the left wing area and penetrated into the passenger cabin. Two of 70 occupants died in this accident, including the training captain (seated in the right seat) who died on impact and one passenger who was unable to escape because he lost consciousness as a result of the smoke in the cabin.

Marcin Bronikowski, a passenger, told Warsaw Radio ZET station that the incident occurred "in a fraction of a second after landing" and that "there was even hand-clapping after the landing."[1]

Causes of the accident

The main cause of the accident was incorrect decisions and actions of the flight crew. Some of the incorrect decisions were taken when information about wind shear was received by the crew. The wind shear was produced by the front passing over the airport, accompanied by intensive variation of wind parameters as well as by heavy rain on the runway itself.

One additional cause was the lack of current wind information at the tower. For that reason no up-to-date wind information could be transmitted to the crew.

Further additional causes were certain design features of the aircraft. Computer logic prevented the activation of both ground spoilers and thrust reversers until a minimum compression load of at least 6.3 tons was sensed on each main landing gear strut, thus preventing the crew from achieving any braking action by the two systems before this condition was met.

Aircraft systems

To ensure that the thrust-reverse system and the spoilers are only activated in a landing situation, the software has to be sure the airplane is on the ground even if the systems are selected mid-air. The spoilers are only activated if at least one of the following two conditions is true:

The thrust reversers are only activated if the first condition is true. There is no way for the pilots to override the software decision and activate either system manually.

In the case of the Warsaw accident neither of the first two conditions was fulfilled, so the most effective braking system was not activated. Point one was not fulfilled because the plane landed inclined (to counteract the anticipated crosswind). Thus the pressure of 12 tons on both landing gears combined required to trigger the sensor was not reached. Point two was not fulfilled either due to a hydroplaning effect on the wet runway.

Only when the left landing gear touched the runway did the automatic aircraft systems allow the ground spoilers and engine thrust reversers to operate. Due to the braking distances in the heavy rain the aircraft could not stop before the end of the runway. The computer did not actually know the aircraft had landed until it was already 125 meters beyond the halfway point of runway 11.

Illustration of distance relative to main strut touchdown. The striped line marks 1400 m, which divides the runway in half. Red indicates the landing gear have not touched down, blue indicates hydroplaning, and green indicates wheels on the ground.

As a result of the accident, Airbus Industrie changed the required compression value from 6.3 tons to just 2 tons per main landing gear.

See also

References

  1. ↑ "Jet breaks up in Poland; 2 dead, 45 hurt." Associated Press/Houston Chronicle. Wednesday 15 September 1993. Section A, Page 11, 4 Star.

Coordinates: 52°09′39″N 20°59′07″E / 52.16083°N 20.98528°E / 52.16083; 20.98528

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