Lufthansa Flight 540 was a scheduled commercial flight for

Lufthansa Deutsche Lufthansa AG (), commonly shortened to Lufthansa, is the flag carrier of Germany. When combined with its subsidiaries, it is the second- largest airline in Europe in terms of passengers carried. Lufthansa is one of the five founding m ...

, serving the Frankfurt– Nairobi– Johannesburg route. On 20 November 1974, the Boeing 747-130 that was operating as Flight 540 was carrying 157 people (140 passengers and 17 crew members) crashed and caught fire shortly after taking off from Jomo Kenyatta International Airport in Nairobi for the last leg of the flight, resulting in the deaths of 55 passengers and 4 crew members. This was the first fatal accident involving a Boeing 747.

Aircraft and crew

Aircraft

The aircraft involved was a Boeing 747-130 registered as D-ABYB and was named ''Hessen.'' It was the second 747 to be delivered to Lufthansa. It made its first flight on 30 March 1970 and was delivered to Lufthansa on 13 April the same year. The aircraft was powered by four Pratt and Whitney JT9D-7 turbofan engines. The aircraft had 16,781 flying hours at the time of the accident.

Crew

The flight crew consisted of 53-year-old captain Christian Krack (who had more than 10,000 flight hours, with 1,619 hours on the Boeing 747), 35-year-old first officer Hans-Joachim Schacke (3,418 flight hours, with more than 2,000 hours on the Boeing 747) and 51-year-old flight engineer Rudolf (Rudi) Hahn (13,000 hours of flying experience).

Accident

As the aircraft was making its takeoff from runway 24 at the Jomo Kenyatta International Airport in Nairobi, the pilots felt a

buffeting Aeroelasticity is the branch of physics and engineering studying the interactions between the inertial, elastic, and aerodynamic forces occurring while an elastic body is exposed to a fluid flow. The study of aeroelasticity may be broadly classi ...

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 from the end of the runway, the 747 airplane crashed in the grass. It then struck an elevated access road and broke up. The left wing exploded and fire spread to the fuselage. 55 of the 140 passengers and 4 of the 17 crew members died.

Cause

The cause of the crash was determined to be a stall caused by the leading edge

slats Super Low Altitude Test Satellite (SLATS) or Tsubame was a JAXA satellite intended to demonstrate operations in very low Earth orbit (VLEO, below 200 km), using ion engines to counteract aerodynamic drag from the Earth's atmosphere which i ...

(strictly speaking, outboard variable camber

leading-edge slats Slats are aerodynamic surfaces on the leading edge of the wing of a fixed-wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack. A higher coefficient of lift is produced as a result of angle of attack and speed, ...

and inboard

Krueger flap Krueger flaps, or Krüger flaps, are lift enhancement devices that may be fitted to the leading edge of an aircraft wing. Unlike slats or droop flaps, the main wing upper surface and its nose is not changed. Instead, a portion of the lower wing i ...

s) having been left in the retracted position. Even though the trailing edge flaps were deployed, without the slats being extended the aircraft's stall speed was higher and the maximum

angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...

was lower. As a result, the aircraft was unable to climb out of ground effect. 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

takeoff warning system A take-off warning system or TOWS is a set of warning signals required on most commercial aircraft, designed to alert the pilots of potentially-dangerous errors in an aircraft's take-off configuration. There are numerous systems on board an aircraf ...

, which would have sounded an alarm if the flaps had not been set for takeoff, did not have a separate warning that the slats' pneumatic valve had not been opened by the flight engineer. The faulty state of the slats should by design have been indicated by yellow warning lights: one for the pilot, and eight for the flight engineer. However, both crew members stated in court that these lights had been green. Three possible explanations have since been offered for this inconsistency: that the morning sun was blinding the cockpit crew and thus hampered color perception, that a construction error could have caused green lights despite the retracted slats, and that the crew lied. None of these possibilities could be conclusively proven. The flight crew was blamed for not performing a satisfactory pre-takeoff checklist, but the accident report also faulted the lack of adequate warning systems that 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. Captain Krack and flight engineer Hahn were dismissed from Lufthansa shortly after, but their dismissals were overturned by a labor court, as there was no investigation report available to rule out the chances of a technical defect. Flight engineer Hahn was charged with criminal negligence, but was acquitted in 1981. This marks the first crashed Boeing 747.

Bibliography