The exact cause of the accident was never determined. At the time of the accident, 90% of the flight test program had been completed, over the course of 42 flights with a total flight time of 20 hours, 15 minutes.
The incident's underlying cause was never ascertained. At the time of the event, 90% of the flight test program had been concluded, comprising 42 flights with a cumulative flight time of 20 hours and 15 minutes.