Today in History

47 Years ago today: On 18 June 1972 a BEA Hawker Siddeley HS-121 Trident 1C crashed near Staines after stalling on climbout, killing all 118 occupants.

Narrative:
Flight BE548 was a scheduled passenger service from London to Brussels. Start-up clearance was given at 15:39 for a scheduled departure time of 15:45. Push-back was not requested until 16:00 due to load re-adjustment. Clearance to taxi was given at 16:03. The HS-121 Trident taxied to runway 28R for takeoff. At 16:06:53 the crew reported ready for takeoff. Takeoff clearance was given and at 16:08:30 the brakes were released.

The standard BEA practice for this particular flight involved a takeoff with 20° flap, leading edge droop (wing leading edge slats) extended and the engine thrust at settings below full power. After takeoff speed should be increased to the initial climb speed VNA (ie, takeoff safety speed, V2 plus 25 knots). The scheduled value of VNA for this flight was 177 knots Indicated Air Speed (IAS). At 90 seconds from brakes-off flaps are to be selected fully up and the engine thrust reduced to the noise abatement settings. At 3,000 feet climb power is to be set and then as the aircraft accelerates and reaches 225 knots the leading edge is retracted and the en route climb established. The minimum droop retraction speed is placarded by the lever and is well-known to all pilots.

The takeoff was normal and at 42 seconds the aircraft rotated, leaving the runway 2 seconds later at 145 knots IAS. At 63 seconds the autopilot was engaged 355 feet above the runway at 170 knots IAS; the IAS speed lock was selected shortly thereafter. At 74 seconds the aircraft started a 20° banked turn to port towards the Epsom Non-Directional Beacon (NDB). At 83 seconds the captain reported ‘Climbing as cleared’. He was then instructed to change frequency and contact London Air Traffic Control Centre.
At 93 seconds the noise-abatement procedure was initiated. On the assumption that the captain was the handling pilot, this would involve the second officer selecting the flaps fully up and operating the thrust levers to reduce power to the pre-calculated figure. At 100 seconds the captain called ‘Passing 1500’ and at 103 seconds the aircraft was cleared to climb to Flight Level 60. This message was acknowledged by the captain at 108 seconds with the terse call ‘up to 60’. This was the last message received from the flight.
At second 114 when the airspeed was 162 knots and the altitude 1,772 feet, the droop lever was selected up putting the aircraft into the area of the stall as the droop started to move. At second 116 the stick-pusher stall recovery device operated, causing the autopilot automatically to disengage and the nose of the aircraft to pitch down and the stick-push to cease as the incidence decreased. Since the elevator trim would stay at its position on autopilot disengagement which at that speed with the droop up would be – the incidence then increased causing a second stick-push at second 124 and a third at second 127. At second 128 the stall recovery system was manually inhibited by pulling the lever. The aircraft then pitched up rapidly, losing speed and height, entering very soon afterwards the true aerodynamic stall and then a deep stall from which at that height no recovery was possible. Impact was at second 150 in a field next to the A30 motorway

Probable Cause:

PROBABLE CAUSE: Immediate causes were:
1) Failure by PIC to achieve and maintain adequate speed after noise-abatement procedures; 2) Droop-retraction 60kts below minimum speed.; 3) Failure to monitor speed error and to observe droop lever movement.; 3) Failure to diagnose reason for stick-pusher operation and warnings; 4) Operation of stall recovery override lever.
A factors was a.o. the abnormal heart condition of the captain.