A navigator fell from an RAF Tornado while flying at about 450mph because his ejector seat had not been properly fitted, an inquest has heard.
Mike Harland, 44, who worked for BAE Systems, died after taking off from RAF Marham in Norfolk in November 2007.
The inquest in Norwich heard his seat slipped from the aircraft as the jet was flying upside down 6,000ft above South Creake, Norfolk.
He was testing the two-seater fighter jet after new parachutes were fitted.
Mr Harland, from Colsterworth, Lincolnshire, suffered multiple injuries and his body was later found in a field near South Creake.
The plane landed safely at Marham and the pilot was not seriously hurt.
Accident investigator Stephen Moss told jurors that the "misengagement" of a locking device which prevented the seat from sliding when the jet flew upside down was the most probable cause of the accident.
Mr Moss said it was "very, very unlikely" that component parts of the locking mechanism had failed.
Coroner Jacqueline Lake was told an RAF Board of Inquiry concluded the cause of the accident to be "the incorrect engagement of the seat locking mechanism on installation of the seat to the aircraft".
Board of Inquiry members made more than 40 recommendations, the inquest heard.
Mr Moss said the tail fin had hit the seat as Mr Harland emerged from the Tornado, causing damage which would have prevented either of two parachutes fitted in the seat headbox from working.
The inquest continues.