Investigation British European Airways Flight 706

1 investigation

1.1 flight recorder analysis
1.2 structural failure
1.3 inspection
1.4 conclusion

investigation

witnesses on ground recalled vanguard exploded in mid-air, lost 1 of wing , plunged onto ground, smoke pouring out 1 of wing. stated heard strange noises during crash. according them, aircraft touched down in 1 field, jumped road, , plowed through grassland 500 yards. gouged ground , burst flames in pit 15 feet deep. 1 of witness stated: “the plane crashed seconds later. there huge ball of smoke , saw 1 of engines flying air. fire spread wreckage waves”. eyewitness stated captain probert had tried execute emergency landing.

there considerable suspicion aircraft had been sabotaged extremists. bea spokesman claimed aircraft sabotaged northern ireland extremists. vanguard had been used on london‐belfast route, though said plane had not been on belfast service @ least 48 hours , stored in edinburgh on friday. however, after preliminary investigation william trench, 1 of investigators aib, stated @ time there no hint sabotage played part in crash.

flight recorder analysis

investigators recovered flight recorder crash site. flight recorder later taken united kingdom further analysis. after investigators downloaded content, found recordings stopped abruptly while flight still in mid-air. investigators concluded sudden explosive decompression caused abrupt stop of recordings.

structural failure

a diagram of rear pressure bulkhead

detailed examination showed failure of rear pressure bulkhead started sequence of structural failure of flight 706. rapid inflation of tailcone , empennage imposed high differential pressure across tailplane skin. causing upper panel become detached main structure. aircraft s flight load caused rapid break , separation of aircraft s tailplane main body. separation caused aircraft pitch rapidly nose down. investigators stated recovery dive impossible.

investigators found severe corrosion @ joint of fuselage skin , rear pressure bulkhead. crack hidden , not detected maintenance crew period of time. crack developed after long period, evidenced presence of nicotine tar stains found on crack. further analysis nature of progressive tear marks on fracture surfaces suggests period short.

investigators concluded crack affected structural integrity of aircraft.

inspection

in final report, investigator stated:

approved maintenance schedule called visual inspection of bulkhead @ relatively long intervals. approach assumed bonding paint , sealing schemes remained intact , effective. in fact, delamination accompanied corrosion can occur between redux bonded doubler , front face of pressure bulkhead. corrosion attack may severe before visual indication apparent @ edge of bonded doubler.

examination aircraft s maintenance record showed maintenance crew had conducted radiographic examination of rear pressure bulkhead of aircraft prior accident. however, investigator questioned effectiveness of technique. technique used examine particular area (the rear pressure bulkhead) of vanguard has been demonstrated ineffective sure means of detecting corrosion. because of difficulty of interpreting photographic plate details resulting complex structure. inspection technique in use, investigators concluded corrosion on aircraft not detectable.

the crack located near toilet of aircraft. investigators stated found liquid around crack. appreciable amount of liquids had been retained @ various times in structure aft of rear pressure bulkhead. because of bea practice of employing personnel clean aircraft, cause inspector not aware of possible fluid contamination on aircraft.

conclusion

investigator concluded cause of accident:

accident caused rupture of rear pressure bulkhead, led separation both tailplanes in flight , caused aircraft dive ground.