Vaid, of Westhill, Aberdeenshire, recalls 6 November 1986 being a “beautiful” day.
“The weather was very nice and calm in Sumburgh,” he told BBC Scotland News.
The Chinook was returning from the Brent field with 47 people on board.
On the approach and as they started to descend, Vaid describes hearing a “whining” noise.
They assumed it was not serious, and was perhaps something such as a heater not switching off.
“Everything was okay, except this noise was coming,” he said. “And it is getting louder, but it didn’t sound dangerous. We couldn’t figure out what it was.”
They then heard an “almighty bang”.