A police spotter plane should be fitted with a revolutionary propeller design by the summer, ending years of complaints about noise.

The crime fighting plane, which is kept at Teesside Airport, between Darlington and Stockton, is shared by the Durham, Cleveland and Northumbria forces.

Trials of noise reduction equipment for the plane, which began more than three years ago, are now finally nearing an end.

Aviation group BN, which was commissioned to carry out the work, says new propellers which reduce the impact of the plane's familiar droning noise should be cleared for use in the next three to four months.

The scimitar propellers, which have a swept shape and turn more slowly than regular propellers, will be fitted first to the police spotter plane.

Final structural safety tests by American manufacturer Hartzell are currently taking place and final approval from the Civil Aviation Authority is awaited.

Mark Wilson, general manager of Isle of Wight-based BN, said: "We realise that operators such as the police want quieter aeroplanes and we are very anxious to take this forward.

"Everything required should be finished during the course of the summer with the propellers then ready for use."

Nigel Dunhill, manager of the North-East Air Support Unit, said: "The trials have been dragging on for some time and there have been delays.

"But BN have indicated that work should be completed by the summer of this year. "The new propellers we are sure will make a substantial difference to noise levels."

Silencers which bolt to the engine exhaust had already been fitted to the spotter plane, said Mr Dunhill.

Last year the Home Office gave the air support unit £250,000 to fund a number of modifications to the plane.

Together with a high speed helicopter used by the unit, both aircraft have dealt with more than 6,000 incidents in the last year.

Middleton-St-George Parish Council has complained about the noise from the plane for some time. Coun Doris Jones said: "In fairness it is an excellent crime fighting weapon, but we have suffered so long with the noise, particularly late at night, in anticipation of something being done.

"Anything reducing the problem significantly should be welcomed."