Investigation Summary
The investigation focused on the rear pressure bulkhead, which separates the pressurized cabin from the unpressurized tail cone. Investigators discovered severe corrosion in the lower part of the bulkhead, specifically beneath a double curvature peripheral doubler plate. This corrosion was exacerbated by fluid contamination, likely from the aircraft's lavatories (sewage) and nicotine stains from cigarette smoke, which had seeped into the structure over years. The corrosion led to delamination of the bonded structure, weakening it until it could no longer withstand the pressure differential at altitude. When the bulkhead finally ruptured, the sudden rush of air into the tail cone created internal pressure that blew the skin of the horizontal stabilizers outward, leading to their separation from the airframe.
Final Conclusions
The accident was caused by the rupture of the rear pressure bulkhead due to undetected corrosion. This rupture led to the separation of both tailplanes in flight, rendering the aircraft uncontrollable. The corrosion remained undetected because the radiographic inspection techniques used by BEA were insufficient to identify the rot beneath the doubler plates, and ground crews frequently cleaned away external fluid stains that would have served as a warning sign of the internal leakage.
Photographic Evidence (1)
Video Analysis
British European Airways (BEA) Flight 706 Aftermath Footage | 2 October 1971 Aarsele, Belgium — Historical news footage showing the crash site in Aarsele, Belgium, including the recovery efforts and the search for the detached tail section.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
Captain E.T. Probert
First Officer
J.M. Davies
Third Pilot
B.J.S. Barnes
Systems & Failure Modes
Rear Pressure Bulkhead
The structural barrier that maintains cabin pressure; its failure caused the explosive decompression.
Horizontal Stabilizers
Detached from the aircraft due to internal overpressure in the tail cone following the bulkhead rupture.
Radiographic Inspection
The maintenance technique used to check for cracks, which failed to detect the corrosion due to poor data interpretation.
Interesting Facts
- 01The aircraft was manufactured in 1959 and delivered to BEA in 1961.
- 02Debris from the tailplane was found approximately 2 miles (3.2 km) from the main crash site.
- 03A passing car on the ground was struck by debris, causing minor injuries to one of its occupants.
- 04Subsequent inspections of the BEA Vanguard fleet found similar corrosion in eight other aircraft.
- 05The failure mechanism was a precursor to the 1985 Japan Airlines Flight 123 disaster, which also involved a rear pressure bulkhead failure.
Safety Actions & Advisories
Revised Corrosion Detection
AAIB and BEA introduced new radiographic and physical inspection techniques specifically designed to detect corrosion in bonded structures.
Aircraft Design Modification
Modifications were ordered to provide ground engineers with better physical access to difficult-to-reach areas within the tail section for visual inspections.