The German Klemm Kl35D, built to train Luftwaffe pilots before the World War Two, was flying from Southend to Old Warden in Bedfordshire last July when the pilot declared an emergency.
It came down heavily in a field next to Earls Lane near South Mimms as the pilot tried to avoid a line of trees.
The 70-year-old pilot was seriously injured.
The pilot "noticed a change in the sound of the engine" just as he was about to contact air traffic control at Luton Airport, the Air Accidents Investigation Branch (AAIB) report said.
He immediately decided to declare an emergency and headed towards the nearest airport at Elstree, but after about five minutes the engine lost power.
The pilot selected the one field into which he felt it was possible to make a forced landing.
During impact, both wings and the undercarriage became detached from the fuselage.
Both the pilot and passenger got out of the cockpit by themselves, but the pilot was taken to hospital.
A classic aircraft which crashed in Hertfordshire last summer had engine failure, a report has concluded.