What happened
On a scheduled international flight returning from Palma to Manchester, an Argonaut aircraft was descending toward its destination during the early morning hours. While being vectored toward the ILS localizer, the aircraft experienced a significant mechanical issue when the number four engine lost power, followed shortly by the failure of the adjacent engine on the same side.
As the crew attempted to manage the emergency, the aircraft's airspeed and altitude steadily declined. The pilot-in-command notified air traffic control of difficulties with engine RPM while attempting to follow instructions for a left turn; however, the aircraft actually turned to the right. During the descent, the flight was unable to maintain its altitude, dropping to approximately 500 feet above the ground as it approached the built-up area of Stockport.
Radar contact was lost as the aircraft flew at low altitude. Eyewitnesses observed that just before impact, the pilot appeared to deliberately reduce power and steer the plane toward a small patch of open ground to avoid more densely populated structures, including a town hall and infirmary. The aircraft struck the ground nearly level with a slight right wing down attitude.
This accident resulted in 72 fatalities (including three crew members and 69 passengers) and 12 injuries.
Findings
Investigations determined that the primary cause of the crash was the loss of power to both engines on the starboard side, which created control difficulties that prevented the pilot from maintaining altitude. The initial engine failure was caused by fuel starvation due to an accidental fuel transfer during flight. The second engine failed either because of continued fuel starvation or because the crew misidentified which engine had failed, preventing them from restoring power in time.
Several contributing factors were identified, including:
- The design of the cockpit fuel valves and their levers, which allowed for a small, difficult-to-detect error that could lead to inadvertent fuel transfer.
- A lack of sufficient warnings regarding the risks associated with the specific positioning of these fuel valves.
- A failure by the airline's crew or engineers to recognize the potential for fuel transfer based on previous flight logs.
- The failure of other operators using similar aircraft systems to communicate known risks regarding inadvertent fuel transfer to aviation authorities.