Corby firm Welwood Roofing Services and the Watford-based Building Research Establishment have been fined £50,000 and £17,500 respectively over the incident, in which 34-year-old Shane Neal died while carrying out work at the former RAF Cardington in Bedfordshire.
Mr Neal was crushed by a truck in Hangar No 1 when the vehicle he had been using to dismantle a fire test rig overturned.
A Health and Safety Executive investigation found Mr Neal was not adequately trained to drive the BRE-provided truck.
HSE inspector Alison Ashworth said: "Mr Neal's death could have been avoided had the companies involved carried out checks to confirm whether or not he knew of the dangers of forklift trucks and how to drive them safely."
Mr Neal's employer, Welwood Roofing Services – which has since gone into administration – pleaded guilty to a breach of the Health and Safety at Work etc Act at Luton Crown Court. In addition to the fine, it was ordered to pay £25,000 in costs.
BRE was ordered to pay £12,000 in costs after pleading guilty to breaching the Provision and Use of Work Equipment Regulations.