Intelligibility of UHF and VHF Transmissions at Fifteen Representative Air Traffic Control Towers

Abstract

A comparison of the intelligibility of UHF and VHF communications was made between “plane to tower” and “tower to plane” at fifteen control towers. A specially equipped plane was flown in a circle with a 20-mi radius for these tests. Voice Communication Laboratory multiple-choice word lists were read by two talkers, one in the plane and the other in the tower. These messages were recorded on tape in both places. Five subjects listened to these recordings in the laboratory, and their responses were scored for accuracy against the original word lists. The percentage of words heard correctly from tower to plane varied from 90% to 38% with an average of 73.7% and was much higher than the corresponding percentage from plane to tower of 63% to 3% with an average of 44.4%. There was very little difference between the intelligibility of VHF and UHF. In general, those towers that had high plane-to-tower scores also had high tower-to-plane scores: the correlation among towers between hearing and being heard was fairly high.