Andrew Doyle/LONDON

THE ROYAL AIR FORCE has been forced to introduce engine modifications on its fleet of Panavia Tornado F3 ADVs (air-defence variants) following the crash in 1994 of an aircraft over the North Sea.

Speed restrictions placed on the aircraft after the accident have been lifted, however, following the introduction of a temporary modification to the engine's fuel system, which Rolls-Royce says allows "virtually full operational usage of the aircraft".

The restrictions had been recommended by R-R as a "precautionary measure" in the aftermath of the crash of an RAF Tornado F3 into the North Sea on 7 June, 1994, following an uncontained engine failure.

The RAF Board of Inquiry concludes that the accident was caused by a catastrophic uncontained failure of the right engine, leading to the failure of both aircraft hydraulic systems and a rear-fuselage fire.

Examination of the failed engine showed that the labyrinth seal around the high-pressure (HP) shaft, which connects the HP compressor to the HP turbine, had failed.

This led to overheating and failure of the HP shaft itself. The specific cause of the labyrinth seal failure was "...not positively determined", says the Board of Inquiry.

Certain HP compressor components are being redesigned for retrofit on existing engines, says the UK Ministry of Defence, while R-R has delivered new labyrinth seals. In addition, maximum fuel-flow stops have been modified to "prevent a recurrence" of the accident, according to the RAF.

R-R says that the redesigned components will be available "before the end of 1995", allowing the F3 to be returned to normal unrestricted operations.

Source: Flight International