An interim report shows pilot David Ibbotson told of poor visibility 15 minutes before the flight plunged, killing him and Cardiff City signing Sala, 28.
The Air Accidents Investigation Branch also revealed Mr Ibbotson, 60, did not have a commercial pilot licence.
The report states they climbed to 5,500 feet then requested a descent at 8.02pm and again 10 minutes later to stay in “visual meteorological conditions”.
Radar readings suggest the plane turned right, came down to 1,600ft and rose sharply again. They lost contact at 8.16pm
The report says: “The wreckage was found about 30 metres from the position of the last secondary radar point.”
The records suggest the Piper Malibu plunged at 7,000ft per minute, around 90mph.
Sala’s body was found with the wreckage, 21 miles off the Channel Islands. Mr Ibbotson has not yet been located.
The plane was in three pieces with its engines thrown from the cockpit, its wings smashed and the tail and fin missing.
Boiler engineer Mr Ibbotson, of Crowle, Lincs, was flying Sala, 29, from Nantes to Wales on January 21.
He had not applied for permission to fly commercially and his private licence entitled him to take money only if his passengers were sharing costs.
The US-based plane does not appear to be registered for commercial use, the AAIB said.
The report read: “The basis on which the passenger was being carried has not been established.”
It added: “We continue to speak to the families of the pilot and passenger to keep them updated on the progress.”