B1, see the earlier links....
.....”One hair-raising flight was the test bed's 44th flight on 7th august 1972. This was the first flight with a new pressure switch to prevent deployment of the thrust reverser on the RB211. With an expected flight time of five hours the aircraft took off laden with fuel. An initial warning light for the thrust reverser was investigated, but the crew decided to continue the flight as they didn't want to dump fuel this early in the flight.
After an initial performance test run at 250 knots at 20,000 feet, the aircraft was being prepared for a second run at 300 knots when the cold stream reverser of the RB211 slid back into the reverse position, sealing off the bypass duct. The effect of this was a reverse idle which produced an initial slight lurch on the aircraft. Shortly afterwards, a more violent lurch occurred, followed by aircraft buffet. There was adverse yaw and roll, and the throttles were closed, initiating a descent before recovering to wings level. Full power was set on the Conways but level flight could not be maintained. The aircraft continued to descend at 2,500 feet per minute as the RB211 was windmilling with the reverser extended.
Fuel jettison was initiated as the equation was quite clear to all on board - the aircraft would hit the ground in approximately twelve minutes unless the weight could be brought down to a value that the Conways could cope with. As the VC10 was aimed at the Bristol Channel, the crew was running through their sea survival kit and ditching drills. As the weight came down, the rate of descent improved, until, at 3000 feet, the aircraft weight was low enough to enable level flight on the thrust available. Fuel dumping was stopped at the coastline and the crew briefed for the approach and landing procedure for this new configuration. A go-around would not be possible with the drag of the RB211 and the available power on the Conways. A safe landing was carried out after a careful, wide circuit.“........