Advances in Decelerating Steep Approach and Landing for Helicopter Instrument Approaches

A true, total operational capability for helicopters during instrument meteorological conditions (IMC) and, in many cases, during night flying conditions will not be realized, in practice, until the helicopter pilot is provided the means with which to perform the same decelerating steep approach and landing (DSAL) maneuver during IMC that he routinely performs under visual flying conditions. This means that the helicopter pilot must, in addition to being provided the means with which to safely guide his helicopter along a precise steep angle approach course, be provided the means with which to perform a normal deceleration to a safe approach termination within a confined landing zone. This maneuver must be accomplished without any visual reference to the outside world. Microwave landing guidance systems, complete with the necessary precision DME, working through unique 4-cue/4-axis flight director (FD) and autopilot (AP) systems, have now extended the helicopter's formerly visual DSAL capabilities into the IMC domain. The intent of this paper is to brief the reader on how this capability has been achieved. This paper describes the instrument decelerating steep approach and landing techniques which were pioneered by the U.S. Army Avionics R&D Activity and expounds on work done by Sperry Flight Systems both independently and under Army contract (see references).