Onboard video shows one of the pilots moving the lever to the "unlocked" position. By itself, that would not trigger deployment of the "feathered" configuration. There's no indication of either pilot actually flipping the switch to change the configuration. So, right now, it looks like a combination of the safety lock being released too early followed by something going wrong mechanically.
-- Roger
To add to what Roger and the head of the NTSB said, the known facts are: 1.) the copilot flipped the feather interlock switch from the locked to the unlocked position at just over Mach 1, approximately 9 seconds after separation, and 2.) there is no evidence, either video or telemetry, to indicate that either pilot activated the feather mode, but the feather mode did activate about 2 seconds after it was unlocked and this action ultimately resulted in the destruction of the spacecraft.
It was stated the proper procedure was to flip the feather mode switch from locked to unlocked when the vehicle past Mach 1.4 (however it was not stated when this should occur, by this I mean on ascent or on descent). (One might assume that the feather deployment code would have some type of time and velocity check to confirm that the time and velocity for crossing Mach 1.4 before proceeding even if the feather mode enable switch was activated early however NTSB has not yet examined the feather deployment code.)
The NTSB statement also reported that motor operations were normal up to the time when the premature feather event occurred. The telemetry and the videos did not indicate a motor problem. No explosive event occurred, and the recovered debris evidence shows that all tanks and the motor chamber were intact and did not rupture.
Feathering normally occurs after apogee to set up reentry, long after the motor has been shut down. In the feather mode the two principal opposing forces are gravity and drag: The vehicle is aerodynamically stable in a high drag mode, and is not very sensitive to small changes in angle of attack, similar to a badminton shuttle cock. If the feather mode is initiated during powered flight, thrust is a third force that must be accounted for. When the feather mode is initiated, the immediate reaction of the vehicle would be to pitch up, and if the motor is burning, the off-axis thrust will cause the vehicle to tumble end over end, and the tumble rate would rapidly increase until either the a boom, the elevator or the wing fails from the combined aerodynamic and high g forces from the off-axis motor thrust. This appears to be what happened.
While the NTSB believes they know
what happened, they are careful to state
they do not know the root cause of the accident. Was it pilot error, improper training, a part failure, a bug in the computer code? They do not know
why the accident occurred and that finding the root cause will take months of study and simulations.
Bob
