 Certain marks of the Vampire were also operated as flying test-beds for the Rolls-Royce Nene engine, leading to the FB30 and 31 variants that were built in, and operated by, Australia.Due to the low positioning of the engine, a Vampire could not remain on idle for long as the heat from the jet exhaust would melt the tarmac behind the aircraft.If the engine did stall in flight, there was no onboard means to re-light the engine, meaning that a forced landing would be necessary.