The stall warning and stall recovery systems were at the centre of the inquiry, which examined in some detail their operation and why the flight crew might have over-ridden them. A three-way air pressure valve (part of the stall recovery system) was found to have been one sixth of a turn out of position, and the locking wire which secured it was missing. Calculations carried out by Hawker Siddeley determined that if the valve had been in this position during the flight then the reduction in engine power for the noise abatement procedure could have activated the warning light that indicated low air pressure in the system. The failure indications might have appeared just prior to take-off and could have accounted for the two-minute delay at the end of the runway. A captain who had flown "Papa India" on the morning of the accident flight noted no technical problems, and the public inquiry found that the position of the valve had no significant effect on the system.