Patent US 4,093,938

There is disclosed an improved annunciator for verbalizing altitude-related messages during the descent of an aircraft. In the past, announcements such as "nine hundred," "eight hundred," etc. were made when the aircraft crossed a respective "hundreds" level. During circle-to-land maneuvers multiple announcements of the same level sometimes occurred, primarily due to small terrain variations which in effect caused the aircraft altitude to vary above and below a "hundreds" level. In accordance with the invention, the annunciator is enabled following a previous announcement only if the aircraft first passes through a mid-"hundreds" level, e.g., 750 feet. Terrain variations are usually no more than twenty feet or so; thus multiple announcements of the same level are inhibited.