Wet runway surface V1.
Ah, okay, thanks. I thought it would be something much more complicated, but I guess sometimes even in aviation things can be simple.
Lufthansa 747-130 crashed on T/O in Nairobi, 20 Nov. 1974 due to the failure of the LE flaps to extend although TE flaps were in the T/O range.
I believe the LE flaps didn´t fail to extend but were rather accidentally retracted again prior to t/o.
This is what my level of information is about this particular accident: The 747 was taxiing to the active RWY, and due to the taxiway having quite a bit of downslope the crew was using idle reverse in order to avoid riding the brakes. Problem is, the 747 retracts the LE flaps when reverse thrust is applied. Apparently this can be overridden somehow (sorry for the lack of details, but I´m not exactly an expert about the systems of a 747, I´m sure someone else will correct me if I´m wrong), but for some reason the crew neglected to do so.
Problem number 2 was that the warning light for the retracted LE flaps was only present on the FE´s panel, but he didn´t notice the warning since he was already facing forward for the departure.
So the crew started the t/o roll and rotated at the calculated Vr speed. The aircraft actually lifted off, but instead of climbing out it wobbled along a few feet above groundlevel (would it be possible that it was flying only due to the ground effect?), and of course since it lifted off without LE flaps it was extremely close to stall speed. The crew was puzzled by the unexpected behavior of the aircraft, and as a first measure they decided to get the gear up in order to gain airspeed. However, when the gear bay doors opened, that was all that was needed to cause enough increase in drag, pushing back the airspeed just enough for the aircraft to stall.
The aircraft hit the ground about one kilometer behind the runway and skidded for another half kilometer before it came to a rest and burned out. A total of 59 people lost their lives in this accident, 4 crew and 55 pax.
The accident report claimed "
the lack of warning of a critical condition of leading edge flap position and the failure of the crew to complete satisfactorily their checklist items" as major contributory factors.