It was June of 1972 and tensions were high between employees of British European Airways. Pilots were nearing a strike, but not all of those employed by BEA were in favour of the action.

Many of the older pilots felt the action was unprofessional. Particularly opposed to the strike was Stanley Key, a highly experienced captain. On the afternoon of June 18, Key was in the crew room at London Heathrow preparing for a flight to Brussels. Another pilot questioned Key regarding his position on the strike to which Key responded with a violent outburst. One of the pilots who witnessed Key's outburst was second officer Jeremy Keighley, a new BEA pilot who was scheduled to fly with Key to Brussels that afternoon.

Also scheduled to fly that day was second officer Simon Tricehurst, a slightly more experienced co-pilot. It was the company's position to have three pilots aboard the aircraft, one of them sitting in seat similar to a flight engineer's seat as the "monitoring" position. The "monitoring" pilot's job was to observe the actions of the captain and co-pilot and assist as directed by the captain. They were also responsible for alerting the crew to any deviations from standard procedure. Because Keighley had not yet had the opportunity to become qualified as a "monitoring" pilot, he would be flying in the right seat while Tricehurst flew in the third seat behind the two pilots.

......It was just after 4pm when the Trident taxied to runway 27R with a full load of 112 passengers. In addition to the crew and passengers, a BEA Vangaurd freighter crew was travelling to Brussels to pick up an aircraft. The captain, John Collins, himself a qualified Trident captain, chose to ride in the jumpseat behind Key. The weather was mild, but there was a slight rainfall from the clouds at 1,000ft. The aircraft took off normally and began a southerly turn just before climbing into the overcast layer. After contacting London Centre, 548 was cleared to 6,000ft, which was tersely acknowledged by Key. This was the final transmission from 548. Less than a minute later, the Trident emerged from the clouds in a nose-high attitude and fell into a field just south of the A30, a major thoroughfare to London. Though there was little post-crash fire, all aboard were killed.

Wreckage of 548...

Although the Trident was not equipped with a cockpit voice recorder (CVR), it was equipped with a flight data recorder (FDR). It became clear during examination of the wreckage that the aircraft was fully functional up to the time of impact and that the accident was caused by lack of airspeed causing a stall. This stall was caused by premature retraction of the leading-edge droops. The only question which remained was why a fully functional aircraft with four qualified pilots on the flightdeck was allowed to get too slow in an improper configuration and stall. The Trident was equipped with a stick-shaker and stick-pusher system. This system physically caused the control yoke to vibrate when a stall was imminent to warn pilots.

If corrective action was not taken, it would then push the control yoke forward, breaking the stall. This system can be overridden by a switch on the control console. Readout of the FDR showed that 6 seconds after Key's acknowledgment of London Centre's clearance to 6,000ft, the droops were retracted. The aircraft was at an airspeed of 162kts, some 63kts below the minimum droop retraction speed of 225kts. This immediately placed the aircraft into a stalled condition which activated the stick-shaker/pusher system.

Activation of the system automatically disengages the autopilot as well. The stick-pusher lowered the nose and unstalled the wings, but with the autopilot disengaged and the elevator trim still set for a climb, the aircraft immediately pitched back up into a stall attitude. The stick-shaker again activated, but before the stick-pusher could lower the nose a second time, one of the crew members turned the system off. Without stick-pusher or crew intervention, the aircraft rapidly pitched up in excess of 30 degrees and entered a deep stall unrecoverable in T-tailed aircraft. It was in this attitude that the aircraft struck the ground, causing total separation of the tail.

Further analysis of the FDR showed that even prior to the retraction of the droops, the aircraft had been operated outside of normal BEA procedures. At London Heathrow, BEA had a noise abatement procedure which involved accelerating to 177kts, retracting the flaps, and then, after passing through 3,000ft, increasing power for a cruise climb and retracting the droops through 225kts. Instead, 548 only reached a maximum of 170kts before reducing power for noise abatement and retracting flaps, at which time airspeed bled off to 157kts.

The aircraft had just entered a turn and started to accelerate again when the droops were retracted. The minimum droop retraction speed is clearly placarded on the control console and is an integral part of all pilot's Trident training. BEA also had a policy prohibiting retraction during turns. Despite all these things, the situation was still recoverable if the crew had either increased speed or immediately re-extended the droops.

Autopsies preformed on the flight crew uncovered some clues as to what may have happened on the flightdeck of 548. Tricehusrt, Keighley, and Collins all appeared to be healthy and normal. Captain Key's autopsy, however, revealed a severe case of narrowing arteries. In addition, there was a tear in the wall of one of the arteries.

Doctors concluded that this tear was a result of a sharp rise in blood pressure not more than two hours prior to the accident. Symptoms were likely to be unconsciousness, with chest pain and disturbance of though processes at the very least. There is little doubt that tensions on the flightdeck would be high with the recent strife between flightcrews regarding the strike. Both Tricehusrt and Keighley were young, inexperienced pilots while Key and Collins were some of the most senior men at the company. In addition, Keighley had witnessed Key's outburst earlier and knew of his temper.

Wreckage of 548

Given this situation, it is unlikely that either of the two younger men would be willing to point out any discrepancies to the captain, especially in the presence of another senior captain. Key was known as a precise and competent pilot and the deviations from procedure were believed to be because of his increasing chest pain and distraction. Investigators did not believe that Keighley would have been responsible for the premature droop retraction. Although he was a new Trident second officer, he was fully trained and capable of flying the aircraft and was fully knowledgeable of the droop limitations. Instead, it was believed that Key, in his pain and distraction, inadvertently retracted them while possibly trying to retract the already retracted flaps. Still, there were three other pilots capable of recognizing and correcting this mistake. It was believed that the crew was becoming aware of Key's degrading condition at this point and were distracted in attending to him.

Tricehurst's notepad was found in the wreckage with the clearance to 6,000ft written down, indicating that he was probably not watching when the droops were retracted. It was widely believed by BEA pilots that the stick-shaker/pusher system was unreliable and it is likely that the crew, when encountering the system activation twice within several seconds, decided that it was acting erroneously and deactivated it. Though the exact chain events could not be definitively concluded, it is clear that something distracted the crew from flying the aircraft and properly intervening when a problem arose.

......After this accident, several recommendations were put into practice at BEA and the rest of the airline industry. The first of these was the addition of a speed limiting device which prevented droop retraction below minimum droop speed. Crews were also trained in stalls which resulted from changes in aircraft configuration. Cockpit voice recorders (CVR) were also installed on all large passenger aircraft in Britain. Finally, BEA changed their medical examination procedure, requiring stress EKGs rather than resting EKGs.