Lufthansa Flight 540
The aircraft involved shortly after delivery to Lufthansa.
|Date||20 November 1974|
|Summary||Design flaw, flight crew error|
|Site||Jomo Kenyatta Int'l Airport
|Aircraft type||Boeing 747-130|
|Flight origin||Frankfurt Airport
Frankfurt, West Germany
|Stopover||Jomo Kenyatta Int'l Airport|
|Destination||Jan Smuts Int'l Airport
Johannesburg, South Africa
Lufthansa Flight 540 was a scheduled commercial flight for Lufthansa operated with a Boeing 747-130, carrying 157 people (140 passengers and 17 crew members). The flight was operating the final segment of its Frankfurt–Nairobi–Johannesburg route. On 20 November 1974 it crashed and caught fire shortly past the runway on takeoff. This was the first fatal accident and third hull loss of a Boeing 747. This was also the third fatal accident involving a wide-body aircraft, after Eastern Air Lines Flight 401 in 1972 and the crash of Turkish Airlines Flight 981 earlier in 1974.
As the aircraft was making its takeoff from runway 24 at the Jomo Kenyatta International Airport in Nairobi, the pilots felt a buffeting vibration. The captain continued the climb and retracted the landing gear. However, as this was being done, the aircraft started to descend and the stall warning system light came on. The aircraft continued to descend and approximately 3,700 feet (1,100 m) from the end of the runway, the 747 grazed bushes and grass. It then struck an elevated access road and broke up. The left wing exploded and fire spread to the fuselage. Of the 157 people aboard, 59 perished (55 passengers and 4 crew members).
The cause of the crash was determined to be a stall caused by the leading edge slats having been left in retracted position. Even though the trailing edge flaps were deployed, without the slats the aircraft's stall speed and maximum angle of attack were much lower, especially at a hot and high airport like Nairobi's with its airport elevation of 5,327 feet (1,624 m). The lower air density at higher altitudes generates less lift and further degrades the aircraft's ability to handle high angles of attack, and the high outside temperature reduced the thrust provided by the 747's four turbofan engines.
The elevation and temperature at the airport were within the capability of the 747, but only with both the leading edge slats and trailing edge flaps extended. With the slats retracted, the aircraft lacked sufficient lift and thrust to continue climbing once out of the ground effect found near the surface. The flight engineer was found to have failed to open the slat system bleed air valves as required on the pre-flight checklist. This prevented bleed air from flowing to the 747's pneumatic slat system and since the leading edge slats on the 747 are pneumatically driven, kept it from deploying the leading edge slats for takeoff. The warning system that would have prevented take off if the flaps had not been lowered did not have a separate warning that the slats' pneumatic valve had not been opened by the Flight Engineer.
The flight crew was blamed for not performing a satisfactory pre-take-off checklist, but the accident report also faulted the lack of adequate warning systems which could have alerted the crew to the problem. Two previous occurrences of this error had been reported, but in those cases the pilots had been able to recover the aircraft in time. After this third deadly incident, Boeing added systems to warn pilots if the slat valve had not been opened prior to takeoff.
As of today, Lufthansa still flies from Frankfurt to Johannesburg, but no longer stops at Nairobi. Also, Lufthansa omitted the "D-ABYB" registration on new Boeing 747-8s (which utilize the old registration numbers of Lufthansa's 747-100s and 747-200s) out of respect of the victims of the crash.
Moorhouse, Earl : Wake Up, It's a Crash! The story of the first ever 747-Jet disaster. A survivor's account. London Corgi 1982 ISBN 0-552-11932-6
- Accident description at the Aviation Safety Network
- Photos of the crashed airliner from AirDisaster.com
- Pre-crash photos of the airliner at airliners.net