Shannon and others have estimated that written English is about 60 percent redundant. These estimates are arrived at by considering linguistic constraints on our use of speech symbols; they do not consider additional restrictions imposed by the audience and the situation in which the speaker finds himself. In order to estimate the effects of such nonlinguistic constraints, an informational analysis has been made of the “sublanguage” used in the control of aircraft by Air Force control tower operators. When the situational, as well as linguistic, contexts are taken into account, the estimated redundancy is raised to 96 percent.