I would go with a problem with the trim actuator.
On the Valiant the normal power control trim, a 4 way joystck, was on the centre consol. The similar manual trim was on the port consol and only reachable by the captain. The power controls were developed from the Frazer Nash gun turret actuator and were electro/hyraulic. The trims were Q feel with big pnumatic cans in the fuselage. The controls, however, had a limit to their effectiveness and if they were overloaded they would stall. The Valiant could revert to manual control and for this the manual trims were electric.
The pitch trim was primarily by adjusting the tailplane incidence. There was a indictor that showed the loading on the elevator and the would be neutralised by use of the power trim. After experience with a similar arrangement on the Canberra the TPI switch was doubled, one power and one operating, to reduce the chance of a runaway. This is what was believed to have happened to WZ 363 at Market Rasen in 1964.
With a practice power control failure, a real one was something that had never been heard of, a Very Heavy aircraft would be flown with assistance from the manual trims. Fortunately down at about 150knots it was manageable enough to land it.
The big problem came if a manual electrically operated actuator ran away or an aileron trim tab was fully over. The power controls could not cope with this and would stall. The captain would then be presented with a hardover on his control spectacles that was outside both pilots strength to correct. Full opposite rudder would only delay the crash and that is what happened to WP222.
Did the actuator run away or was it selected before takeoff? During the pre-start check the manual trims are checked throughout their range and it is just possible that they were left in a full-over position as they cannot be seen from the cockpit. During the take off and the initial climb the power controls would have been able to cope with the out-of-trim forces until the aerodynamic loading became excessive and then it would have stalled.
We will never know because there is no way they would have positivily found out whether human or mechanical failure could have caused the accident. What did happen was that the operating range of the manual trim tabs was reduced from 4.45 ins to 1,39 ins so that with a full runaway the aircraft was still controllable.
Last edited by Fareastdriver; 6th Sep 2012 at 07:37.