British European Airways Flight 706

BEA Flight 706

G-APEC at London Heathrow in 1965.
Accident summary
Date 2 October 1971 (1971-10-02)
Summary Explosive decompression, leading to structural failure and loss of control
Site Aarsele, Belgium
Passengers 55
Crew 8
Fatalities 63 (all)
Injuries (non-fatal) 1 (minor, ground)
Survivors 0
Aircraft type Vickers Vanguard
Operator British European Airways
Registration G-APEC
Flight origin Heathrow Airport, London, United Kingdom
Destination Salzburg Airport, Salzburg, Austria

British European Airways Flight 706 (BE706/BEA706) was a scheduled flight from Heathrow Airport in London, United Kingdom to Salzburg-W. A. Mozart Airport in Salzburg, Austria. The flight was operated by a Vickers Vanguard with a U.K registration of G-APEC. On 2 October 1971, whilst en route at 19,000 ft (5,791 m), 35 minutes after takeoff,[1] the rear cabin pressure bulkhead failed. The resulting pressurisation of the tail section caused the surfaces of the tailplanes to separate, weakening them to the point that they broke off. Without a horizontal stabiliser the aircraft entered an uncontrollable dive. The aircraft crashed near Aarsele, Belgium, killing all 63 passengers and crew on impact.[2] A piece of debris from the aircraft struck a passing car, causing minor injuries to one of its occupants.

Investigators, in attempting to determine the cause of the accident, found corrosion in the lower part of the rear pressure bulkhead underneath plating that was bonded to the structure. The bulkhead had been eaten away. Fluid contamination, perhaps from the lavatory, was thought to have been the root cause for the corrosion.[3] The corrosion was not detectable by then-current inspection techniques. The Belgian Civil Aeronautics Administration wrote the report and the British Air Accidents Investigation Branch had accredited personnel assisting the investigation.[4]

Flight

Flight 706 took off from Runway 28 L of London Heathrow Airport at 09:34 local time with 55 passengers and 8 crew members[5].. After take off, Flight 706 was routed via Epsom, Biggin and Detling in accordance to the "Dover One" standard instrument departure clearance. The crew of Flight 706 later reported over the Dover VOR at 09:54 local time. At the time, Flight 706 was climbing through 14,200 feet. At 10: 01, the communication was handed over to Brussels Air Traffic Control[6].

The crew then reported passing over the Wulpen VOR with the aircraft level at FL190[5].

Just five minutes after this communication, the crew of Flight 706 transmitted "we are going down, 706, we are going down" to Brussels Tower. The crew later declared emergency and called "mayday mayday" for several times. The crew also stated the phrase "out of control" several times. At one point they stated that there was no rudder control. Their calls were accompanied by several background voices[5][6].

The last transmission from Flight 706 was recorded at 10:10:30. Brussels Tower immediately contacted Flight 706 for several times. However, there were no answers from Flight 706[5]. Witnesses on the ground saw the tailplane of Flight 706 detached and subsequently Flight 706 entered a nose-dive. The flight kept diving and crashed into a farm land near Aarsele, Belgium and exploded on impact. All 55 passengers and 8 crew members were killed. At least one person on the ground was injured after pieces of the debris struck a passing car[5].

Rescue services were immediately dispatched. Investigators were deployed and immediately searched the aircraft's black box. Crisis center was set up in Salzburg to handle the relatives of the victims of Flight 706. Searchers stated that most of the bodies were not intact. One searcher said “as for the bodies, what we have found so far is barely enough to reconstitute one body[7].”

Passengers and crews

The aircraft was carrying 55 passengers and 8 crew members. News report stated that there were 37 British passengers on board the aircraft. At least 4 Japanese and 11 Americans were also on board the aircraft. Further reports also confirmed the presence of 8 Austrians on board the flight[8][9]. Two notable fatalities among the passengers were the British hat designer Otto Lucas and an Austrian academic, René Marcic.[10]

The Captain was identified as 40 year old Captain E.T Probert. At the time of the accident, he had accumulated a total flying hours of 9,260 hours, in which 1,927 hours were on the type. The co-pilot was 38 year old J.M Davies, who held a Vickers Vanguard rating. He had a total flying hours of 3,386 hours, in which 764 hours were on the type. The aircraft was also carrying a third pilot, identified as 27 year old B.J.S Barnes with a total flying hours of 2,237 hours, in which 1,903 hours were on the type and a supernumerary, identified as Captain G. Partridge[5].

Investigation

Witnesses on the ground recalled that the Vanguard suddenly exploded in mid-air, lost one of its wing and plunged onto the ground, with smoke pouring out from one of its wing. They stated that they heard "strange noises" during the crash. According to them, the aircraft touched down in one field, jumped a road, and plowed through grassland for 500 yards. It gouged into the ground and burst into flames in a pit 15 feet deep. One of the witness stated: “The plane crashed seconds later. There was a huge ball of smoke and we saw one of the engines flying into the air. The fire spread from the wreckage like waves”. Another eyewitness stated that Captain Probert had tried to execute an emergency landing[8].

There was considerable suspicion that the aircraft had been sabotaged by extremists. A BEA spokesman claimed that the aircraft was sabotaged by Northern Ireland extremists. The Vanguard had been used on the London‐Belfast route, though he said the plane had not been on Belfast service for at least 48 hours and was stored in Edinburgh on Friday. However, after a preliminary investigation by William Trench, one of the investigators from AIB, stated that at the time there was no hint that sabotage played a part in the crash.[10]

Flight recorder analysis

Investigators recovered the flight recorder from the crash site. The flight recorder was later taken to United Kingdom for further analysis. After investigators downloaded the content, they found that the recordings stopped abruptly while the flight was still in mid-air. Investigators concluded that a sudden explosive decompression caused this abrupt stop of the recordings[5].

Structural failure

A diagram of the rear pressure bulkhead

Detailed examination showed that the failure of the rear pressure bulkhead started the sequence of structural failure of Flight 706. The rapid inflation of the tailcone and empennage imposed a high differential pressure across the tailplane skin. This causing the upper panel to become detached from the main structure. The aircraft's flight load then caused the rapid break up and separation of the aircraft's tailplane from its main body. This separation caused the aircraft to pitch rapidly nose down. Investigators stated that recovery from this dive was impossible[5].

Investigators found a severe corrosion at the joint of the fuselage skin and the rear pressure bulkhead. This crack was hidden and probably was not detected by maintenance crew for a period of time. The crack was probably developed after a long period, evidenced by the presence of nicotine tar stains found on the crack. Further analysis from the nature of the progressive tear marks on the fracture surfaces suggests that the period was short[5].

Investigators concluded that the crack affected the structural integrity of the aircraft[5].

Inspection

In its final report, investigator stated[5]:

"The approved maintenance schedule called for visual inspection of the bulkhead at relatively long intervals. This approach assumed that the bonding paint and sealing schemes remained intact and effective. In fact, delamination accompanied by corrosion can occur between the redux bonded doubler and the front face of the pressure bulkhead. The corrosion attack may be severe before any visual indication is apparent at the edge of the bonded doubler."

Examination from the aircraft's maintenance record showed that maintenance crew had conducted a radiographic examination of the rear pressure bulkhead of the aircraft prior to the accident. However, investigator questioned the effectiveness of the technique. The technique used to examine this particular area (the rear pressure bulkhead) of the Vanguard has been demonstrated to be ineffective as a sure means of detecting corrosion. This is because of the difficulty of interpreting the photographic plate details resulting from the complex structure. With the inspection technique then in use, investigators concluded that the corrosion on the aircraft was not detectable[5].

The crack was located near the toilet of the aircraft. Investigators stated that they found liquid around the crack. Appreciable amount of liquids had been retained at various times in the structure aft of the rear pressure bulkhead. Because of BEA practice of employing a personnel to clean the aircraft, this could cause the inspector to be not aware of possible fluid contamination on the aircraft[5].

Conclusion

Investigator finally concluded the cause of the accident[5]:

"The accident was caused by the rupture of the rear pressure bulkhead, which led to the separation both tailplanes in flight and caused the aircraft to dive into the ground."

Aftermath

British European Airways immediately implemented a new technique in detecting corrosion. It was later revealed that eight Vanguards of their fleets suffered the same crack as G-APEC[5].

See also

References

Coordinates: 50°59′27″N 3°26′20″E / 50.99083°N 3.43889°E / 50.99083; 3.43889

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