Traces of ash from Iceland's Eyjafjallajökull volcano found in the engines of four UK Typhoon aircraft have forced the Royal Air Force (RAF) to suspend air training in Lincolnshire.
The Typhoon aircraft are high-performance jets, hence the extra caution, an RAF spokesman said on the BBC
The Civil Aviation Authority (CAA) pointed out that military planes fly much faster and suck in far more air than their civilian counterparts.
The CAA said that work to clear the UK for flying did not take military jets into account as they are different to commercial airplanes.
The authority adds that the "all clear" for civilian aircraft to return to the skies still stands and there have been no reports of any ash damage for commercial planes.