On Four Engined BA-146s, two engines have hydraulic pumps, and two have electrical generators. If you taxi the airplane only on the two engines with generators, you only have a few brake applications available before the hydraulic accumulators run out of brake pressure. The Avro RJ.85 was had received a maintenance check and was being taxied back to the terminal. The mechanics were not able to stop the plane in time. It collided with the jetway at gate C2, causing considerable damage to the jetway as a well as the airplane. The nr.1 engine was almost entirey ripped off its mountings and the flight deck sustained serious structural damage.

don't see the picture below? click here for help