The helicopter crash that killed British Superbike champion Steve Hislop was caused by rotor blades striking the tailboom, a report has found.
The crash happened in July 2003
Hislop, 41, died when the R44 he was piloting crashed near his birthplace of Hawick in the Scottish borders in 2003.
The loss of control could have resulted from "mishandling of the controls", the Air Accidents Investigation Branch (AAIB) said.
But it added that an aircraft malfunction "could not be eliminated".
The AAIB said available evidence indicated the accident on 30 July 2003 followed a main rotor blade strike on the tailboom, probably caused by excessively low main rotor speed.
The report said: "The control loss and low rotor RPM (revs per minute) may have resulted from spatial disorientation and mishandling of the controls, but the possibility that aircraft malfunction had contributed to the accident could not be eliminated."
Hislop, a father-of-two who lived on the Isle of Man, was flying from Hawick to Wycombe Air Park in Buckinghamshire and had decided to take a western route via Carlisle.
Low cloud was around and a right turn he made just south of Teviothead, near Hawick, indicated that he had decided to divert from the original routing and to either land, turn back or route further west.
Mr Hislop was Isle of Man TT champ 11 times
The report said Hislop had probably entered cloud and that "such an entry into cloud could have been inadvertent, possibly coinciding with a distraction such as studying or refolding a map, or could have been made because of concern about terrain clearance".
The AAIB said that having flown up from Wycombe to Hawick two days before, Hislop had told a friend he had an enjoyable flight and that "his only problem was preventing the helicopter 'wobbling' when he attempted to fold his map".
The report said that having probably entered cloud, the helicopter entered a rapid descent and the main rotor blades struck the tailboom.
Most of the tailboom detached, the rotors virtually stopped and the helicopter crashed.
The AAIB issued a number of safety recommendations including asking manufacturers Robinson to include in its pilot's operating handbooks a warning of the possibility of a hazardous loss of rotor speed in certain manoeuvres.
Hislop won the British Superbike title in 1995 and 2002 and had been the Isle of Man TT champion 11 times in his career.