Word Intelligibility of U. S. Navy Aircraft Radios

Abstract

Two types of in-flight recordings were made: (1) actual radio/intercom voice messages on operational flights and (2) standardized word lists read by flying observers on routine test flights. An experienced civilian listener who lacked any experience or knowledge of air operations transcribed 34% of the operational recording, an experienced U. S. Navy Chief Petty Officer Air Controller 68%, and an experienced U. S. Navy aviator 90%. The standardized word lists were listened to by typical U. S. Navy enlisted men. The lists included the 1000 phonetically balanced (PB) words, the Fairbanks rhyme test (FRT), the modified rhyme test (MRT), the Voiers diagnostic rhyme test (DRT), Clarke's medial vowel rhyme test (VRT), and a specially developed brevity code—phonetic alphabet word test (BREV). Scores on the FRT, MRT, and BREV words were equivalent and therefore the easier-to-administer standardized tests (FRT or MRT) can be considered valid alternatives to words actually used operationally. Scores on the PB tests were low, and scores on the VRT and DRT were high. Analysis of the diagnostic words showed the most frequent consonant pair confusion on aircraft radios to be V/B; the vowel EE (beat) was the worst “carrier” vowel, while EH (bet) was the best. Nasality was an intelligible attribute at good speech-to-noise (S/N) ratios but very bad under bad listening conditions. Voicing and sibilation were the more intelligible attributes when listening at low S/N ratios.