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 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. See also List of aircraft accidents and incidents resulting in at least 50 fatalities Bibliography 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. References External links () Cockpit Voice Recorder transcript and accident summary Airliner accidents and incidents caused by pilot error Airliner accidents and incidents caused by design or manufacturing errors Aviation accidents and incidents in 1974 Aviation accidents and incidents in Kenya 540 Accidents and