A Nimrod aircraft which exploded in mid-air killing 14 servicemen was not safe to fly, due to a "fundamental" design flaw.
The 37-year-old Nimrod exploded minutes after undergoing air-to-air refuelling near Kandahar on 2 September 2006.
The crew had no means of tackling the initial fire and were forced to attempt an emergency descent to an air base, but at 3,000ft the aircraft exploded into flames.
At a hearing at Oxford Coroner's Court, Air Commodore George Baber said mistakes were made during a hazard assessment which could have identified the fault that caused the explosion, The Herald reports.
The explosion was caused by fuel leaking into a dry bay and igniting on contact with a hot air pipe.
Baber says having fuel couplings in the same compartment as a hot air pipe is a "fundamental design flaw".
Baber led an Integrated Project Team, and together with BAE systems carried out a comprehensive hazard analysis of the Nimrod plane before the Afghanistan crash.
He said the possibility of the explosion in the dry bay was graded as "improbable", but he says it should have been graded higher which would have then warranted further action.
"At the heart of this was a fundamental design flaw. We failed to catch that design flaw," he says.
By Elizabeth Clifford-Marsh