Powell, who played with Black Sabbath, Rainbow and Whitesnake, was killed when his powerful black Saab 9000 turbo had a puncture on 5 April.
He was driving up the M4, near Bristol, on his way to visit his girlfriend Sharan Reeve in Cardiff. She heard a "terribly loud noise", then silence, as she talked to him on the phone.
In a statement, Ms Reeve said that Powell had just told her he was having problems finding fifth gear, and hoped the engine would not seize up as he was going so fast.
Then she heard him say: "Oh shit", and the line went silent.
She kept trying to ring him back until she realised something was wrong and contacted the police. Powell, 50, was found to be slightly over the drink-drive limit after the car spun, hit the central kerb, and came to rest on its roof.
Paul Forrest, the Bristol coroner, recorded a verdict of accidental death.