Reason
The Soviet Accident Investigation Committee released (according to ICAO standard) the result of CVR & FDR data analysis.
CVR transcript:
00s (Takeoff roll begin)
10s "Time?" "Time is OK." "It's a bit slow..."
25s "Yes." "What?" "We are going."
30s "V1." at 129kt(IAS)
40s "Rotation." "Attention." at 145kt
45s "V2." at 154kt
50s (Mechanical sound)
55s "What's up?" "Spoiler!" at 350ft
60s "What's this?!" "Sorry..." "Left clear." at 300ft
65s "Engine! Engine! No.2! No.2 Engine!" at 100ft
70s (Sound of impact)
The survivors reported 3 abnormal situations indicating an engine failure, which matched the description of eye-witnesses on the ground:
- Abnormal vibration causing hand luggage to fall from overhead bins during the takeoff roll.
- The feeling of slowing down & falling immediately after leaving the ground.
- Engine bursting into flames.
The direct reason to the crash was an excessive nose-up attitude leading to a stall. The cause was determined to be one of the following by both sides (Japanese & Soviet investigating personnel):
- The accidental deployment of the spoilers during takeoff by the copilot.
- To deal with the asymmetric thrust of engine 1 & 2, the nose was inappropriately brought.
- Furthermore, after inspecting the wreckage, it was found that despite winter conditions, the anti-ice device of the engines was not activated. Thus, it was possible that the engine thrust diminished due to ice buildup at the air intake.
Based on the above, the sequence of the entire accident could be presumed (but not determined) that:
- During the take off roll, the copilot tampered with the ground spoiler lever, while saying "This is not fitting in smoothly", then forgot to reset it to the correct position. So, despite the ground spoiler is for use immediately after landing only, the plane had to take off with it extended, generating excessive drags leading to insufficient acceleration and abnormal vibration.
- After lift off, the inappropriate nose-up input caused excessive pitch angle, which either further reduced the airflow into the ice-covered engine, which was already providing insufficient thrust, or caused the ice blocks, built up in the front edge of the wing, to be ingested by the engine.
- As a result, the engine's compressor stalled, back-fired, and substantially lost thrust, leading the plane to stall.
There was a largely believed theory that the copilot mistook the ground spoiler lever as the landing gear lever. However, on DC-8s, they were placed far from each other for ergonomic reasons, thus rendering it unlikely.
Read more about this topic: Japan Airlines Flight 446
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