 Various techniques have been devised to determine the integrity of the rear pressure bulkhead; these have been used not only to inspect in-service examples but also in the design process, helping to design efficient bulkheads that possess sufficient strength to ensure a safe operational life.In 1971, British European Airways Flight 706 crashed in Belgium, killing all 63 on board; the cause was determined to be corrosion of the rear pressure bulkhead by fluid contamination, perhaps from the lavatory.The corrosion was not detectable by the inspection techniques at the time.