Letter: Air of confusion

Sir: Professor Hughes and Michael Fadil (letters, 11, 22 September) both miss an insuperable practical difficulty in the automatic selection of radio frequencies for aircraft.

I am a private pilot operating out of East Midlands Airport. On every flight I am required to change between Tower and Approach frequencies at a time and location determined by Air Traffic Control. Within the same immediate area I might also need to talk to the busy aerodromes at Hucknall, Nottingham, Derby, Leicester, Langar, RAF Newton and Tatenhill, and to radar services at RAF Waddington and RAF Cottesmore. Airline pilots flying over the same spot will need to talk to Daventry Airways Controllers, and none of the others.

For safety reasons, before changing frequencies I must tell the station I am leaving, and in some cases ask permission. How is each station's electronics to "know" which aircraft to lock on to its own frequency, and when?

CLIVE TEALE

Beeston, Nottinghamshire