Stockport Air Disaster - Investigation

Investigation

MAN
EGCC British Midland G-ALHG crash site, situated amongst urban areas of Greater Manchester

Investigators with the Accidents Investigation Branch (AIB) determined that the aircraft had run out of fuel because of a previously unrecognised flaw in the model's fuel system. The Argonaut is equipped with eight fuel tanks connected in pairs by selector valves. Each pair of tanks feeds one engine, but there is also a cross-feed system whereby fuel from any pair of tanks can be routed through the system if necessary. It was discovered that if the selector valves in the cross-feed system were just a few degrees off the normal "off" setting, fuel could inadvertently bleed through the valves. This could cause one pair of tanks to empty completely in flight, and the engine fed by the empty tanks would stop. Moreover, although the selectors were designed to "click" when they were set correctly, the click was not discernible unless the pilot leaned forward in his seat, an impossibility given the requirement for Argonaut pilots to wear snug shoulder harnesses during flight. This tendency had been noticed by pilots of other Argonauts in the past, but neither British Midland nor the other airlines using the Argonaut (Trans-Canada Airlines and Canadian Pacific Airlines) had reported it to the manufacturer or to British Midland. Without this information, the AIB believed that it would have been extremely difficult for the pilots of G-ALHG to determine the exact nature of the emergency.

A fuel problem had been noted on the aircraft five days earlier, this only came to light 4 months after the crash. A third contributory factor was tiredness: the Captain had been on duty for nearly 13 hours. This was within legal and operational limits but the inquiry noted that he had made several errors in repeating ATC messages.

The AIB also examined passenger and crew survivability during the accident. Autopsies on the passengers showed that although those in the very front of the fuselage had been killed by rapid deceleration injuries, those further aft had suffered massive crushing injuries to their lower legs that prevented them from escaping the burning wreckage. Investigators discovered that the bracing bars meant to keep the rows of seats separate were too weak to prevent the rows from collapsing together like a concertina, and determined that had the bars been adequately strong, most of the passengers would have been able to escape the aircraft.

Although news reports stated that the pilot chose to crash in an open area, the AIB found no evidence to support this belief. The aircraft happened to be over an open area at the time the starboard engines cut out, and AIB investigators believed that the aircraft was completely uncontrollable after the loss of power. The captain, who survived, did not remember the accident sequence, and the first officer died. A number of witnesses to the final seconds aloft of the aircraft claim to have seen the aircraft make a very pronounced turn to port and was quickly levelled out before descending into the Hopes Carr crash site. This strongly suggests that although struggling to control the aircraft at critically slow speed Captain Harry Marlow did exert a degree of control and probably did in fact put the aircraft down into open space, albeit an extremely small one. The AIB inquiry cleared Captain Marlow of all blame.