RIP, indeed, and condolences to their surviving daughter.
I have read the
Air Accident Investigation Branch report, which didn't reach complete conclusions as to what happened. There was radar evidence, both primary radar (the one that sends a radar wave and waits for the reflection) and the Secondary Surveillance Radar (which reads the transponder on the aircraft) for almost the entire flight.
It looks as if the flight went normally until the pilot hit cloud close to Dunkeswell. There were reports of an aircraft sounding like it was doing acrobatics above the clouds, and the radar showed sudden climbs and falls. The inspector speculated that the pilot may have left the autopilot engaged (it should be off before lining up to land), and may have made control inputs with the control yoke that the autopilot corrected. This will put the aircraft out of trim. Add to that the pilot being in cloud, with the disorientation that causes, and it looks as though he finally stalled and simply dropped to the ground. The damage showed a high angle of attack, suggesting a stall.
The pilot held a IMC rating which permitted flight in cloud, but that would not have permitted him to make an instrument landing in the conditions on the day - even if Dunkeswell had the equipment. His correct course of action would have been to say "I'm not landing there!", then diverted to Exeter. I think I read that they were flying to Dunkeswell to pick up another daughter, which may have had an influence on the decision to try to land, but once he got lost in the cloud, things went from bad to irretrievable. "Press-on-itis" is the slang term.
Of note is the immense level of detail gone into by the
AAIB▸ . Just about every component that could have had an effect on the performance of the aircraft was taken apart and examined minutely, and test flights with a similar plane were undertaken to test the theory of the autopilot being on, and to examine the accuracy of radar coverage - the aircraft was still visible on Heathrow's radar.