Lufthansa Flight 2904
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| Summary | |
|---|---|
| Date | September 14, 1993 |
| Type | Overshot runway, Pilot Error |
| Site | Warsaw, Poland |
| Fatalities | 2 |
| Injuries | 68 |
| Aircraft | |
| Aircraft type | Airbus A320-200 |
| Operator | Lufthansa |
| Tail number | D-AIPN |
| Passengers | 64 |
| Crew | 6 |
| Survivors | 68 |
Contents |
[edit] Description of the incident
Lufthansa Flight 2904 was an Airbus A320-200 which overran the runway, in Okęcie International Airport on September 14, 1993. It was a flight from Frankfurt, Germany to Warsaw, Poland.
Lufthansa Flight 2904 was cleared to land on Okęcie International Airport and was told of the existence of windshear on the approach. To compensate for the windshear, the pilots attempted to touch down with the aircraft banked slightly to the right. Additionally they landed with a speed about 20 kts 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 touch down, the assumed crosswind turned out to be a tailwind. Due to the tailwind of approximately 20 kts and the increased speed the airplane hit the ground at approximately 170 kts and far beyond the normal touchdown point. The aircraft's right gear touched down 770m from the runway 11 threshold. The left gear touched down 9 seconds later, 1525m from the threshold. Only when the left gear touched the runway did the ground spoilers and engine thrust reversers deploy, these automatic systems depending on oleo strut (shock absorber) compression. The wheel brakes, depending on wheel rotation being equivalent of circumferential speed of 72 knots began to operate after about 4 seconds. 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 and rolled 90m 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. Only two of 70 occupants died in this accident, the co-pilot 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.
[edit] Causes of this accident
The cause of the accident were incorrect decisions and actions of the flight crew taken when the information about windshear at the approach to the runway was received. Windshear was produced by the front just passing the aerodrome; the front was accompanied by intensive variation of wind parameters as well as by heavy rain on the aerodrome itself. Actions of the flight crew were also affected by design features of the aircraft which limited the feasibility of applying available braking systems as well as by insufficient information in the aircraft operations manual (AOM) relating to the increase of the landing distance.
[edit] Details about the design features of the aircraft
The main cause of this accident is the delayed effectivity of the braking system. It turned out to be caused by a failure in the landing-logic of the aircrafts software. Another fact that contributed to the accident was that the pilots had never been instructed on how the braking system of the airplane worked.
To ensure that the thrust-reverse and the brake flaps are only activated in a landing situation, one of the following conditions has to be true:
- the airplane is lower than 3 meter and there must be a weight of over 12 tons on each landing gear
- the wheels of the plane turning with more than 72 knot
In the case of the Warsaw accident neither of these 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 possible windshear). Thus the pressure of 12 tons on both landing gears required to trigger the sensor was not reached. Point two was also not fulfilled because of a hydroplaning effect on the wet runway. The wheels were not accelerated to the required speed, so the braking systems were not activated.
So the delay of 9 seconds from the ground touch until the activation of the thrust-reverse and the brake flaps meant that until this moment neither of the two above-listed statements were fulfilled. If the pilots had received precise instruction on the implementation of the braking system of the A320, they could have avoided this catastrophe by fulfilling at least one of the two required conditions to activate the thrust-reverse and brake flaps.
[edit] Consequences of the accident
Airbus discovered that the catastrophe could have been prevented, if the logic would have been reworked. But instead of modifying the logic, Airbus only exchanged the chassis sensors. Therefore the A320 got a new chassis, with a sensor that triggered at a pressure of 2 tons instead of 12 tons.
