Lufthansa Flight 540 was a scheduled commercial flight for Lufthansa, serving the Frankfurt–Nairobi–Johannesburg route.

On 20 November 1974, the Boeing 747-130 that was operating as Flight 540 was carrying 157 people (139 passengers and 18 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 54 passengers and 5 crew members. This was the first fatal accident involving a Boeing 747. As of 2024 it remains the deadliest accident ever for Lufthansa.

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.

The flight crew consisted of 53-year-old Captain Christian Krack (who had 10,464 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 50-year-old Flight Engineer Rudolf "Rudi" Hahn (13,236 hours of flying experience ).

After a change of crew, flight 540 was due to take off from Nairobi shortly before 8 a.m. local time under the leadership of flight captain Christian Krack, bound for Johannesburg. At 07:52 local time, the ‘Hessen’ was cleared for take-off by the tower in Nairobi. Co-pilot Hans-Joachim Schacke was responsible for the aeronautical handling of the route. Rudi Hahn sat at the flight engineer's console to the right behind the pilots. The take-off weight of the 747 was 254 tonnes, well below the maximum take-off weight. As the Austrian aviation journalist Patrick Huber writes in his book ‘Lufthansa Flight 540: Der erste Jumbo-Absturz’, ‘the maximum take-off weight (MTOW) of the “Hessen” on that day was theoretically around 284,000 kilograms’. This meant that the take-off weight was around 30 tonnes below the maximum permitted take-off weight on that day.

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 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. 54 of the 139 passengers and 5 of the 18 crew members died.

The commander and flight engineer were unable to open the emergency escape hatch in the cockpit roof or the crew service door on the upper deck (where there was an emergency slide) and jumped through the debris behind the cockpit (the stairs were blocked) to the lower deck. They then crawled out through holes in the hull. The first officer, who was still in the cockpit, finally managed to open the emergency escape hatch in the roof of the ‘Hessen’ and abseiled down around 9 metres into the air amidst the flames that were blazing all around the aircraft.

The cause of the crash was determined to be a stall caused by the leading edge slats (strictly speaking, outboard variable camber leading-edge slats and inboard Krueger flaps) 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 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, 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 no investigation report was available to rule out the possibility of a technical defect.

Flight engineer Hahn was charged with criminal negligence, but was acquitted in 1981. The accident was the first fatal crash involving a Boeing 747.

In fact, there are indications that Lufthansa already knew about problems with the slats before the crash. So it is still disputed to this day whether the crew, especially the flight engineer, actually made a mistake. Even before the crash of the ‘Hessen’, other jumbo operators had repeatedly experienced problems with the slats. British Airways and KLM therefore equipped their Boeing 747s with a non-mandatory additional warning system for the position of the slats, while Lufthansa did not. In 2014, the German investigative journalist and lawyer Jens M. Lucke also revealed that British Airways had invited Lufthansa to a meeting in London five months before the crash of the ‘Hessen’ and informed them about the problems with the slats. And just two months before the crash of Lufthansa Flight 540 in Nairobi, Lufthansa had a serious incident: although the indicator lights for the slats showed ‘green’ (extended), the slats were actually not extended. It was only because the highly experienced check captain distrusted the displays and took a look out of the window that this fact was noticed before take-off, as Jens M. Lucke explained in an interview with Patrick Huber. Boeing itself also admitted during the accident investigation that the display for the position of the slats could sometimes be incorrect.even with evidence, the captain and engineer were never brought back.

• List of aircraft accidents and incidents resulting in at least 50 fatalities

• Moorhouse, Earl (1982). Wake Up, It's a Crash! The story of the first ever 747-Jet disaster. A survivor's account. London: Corgi. ISBN 0-552-11932-6.
• Huber, Patrick (2024) Lufthansa Flug 540: Der erste Jumbo-Absturz. Berlin, Epubli, ISBN 978-3-759875-25-9

The final report is this work:

• "Report on Accident to Boeing 747 Registered D-ABYB which occurred on 20th November 1974 at Nairobi Airport, Kenya." East African Community Accident Investigation Branch (Nairobi), 1976. Worldcat entry.

External images
Pre-crash photos of the airliner at airliners.net
Pre-crash photos of the airliner at JetPhotos.com

• Accident description at the Aviation Safety Network
• Photos of the crashed airliner from AirDisaster.com (Archive)
• Cockpit Voice Recorder transcript and accident summary