The man, from Welwyn Garden City, died at the scene of the crash in Luffenhall, Hertfordshire, at about 10:00 BST on Tuesday, police said.
Witness Peter Broadhurst said the Kolb FireFly came down "very steeply" and "hit the ground with a big whump noise".
The Air Accidents Investigation Branch (AAIB) has been examining the wreckage.
The pilot was found by agricultural contractor James Irwin, who said: "I didn't see it come down, but saw it in the corner of my eye as I drove past at about 10:15."
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"I went over to it and you could see he was dead. He was just wearing an open-faced helmet.
"The engine was still running and petrol was coming out of the tank. I rang for the ambulance and fire brigade. They were here pretty quickly."
The deceased was the only person on board the single-seater ultralight aircraft, which was the subject of another AAIB investigation after its pilot was forced to land when the aircraft lost its propeller shaft during a flight in July 2013.
A pilot in his 70s has died after the light aircraft he was flying crashed in a field.