IFR Design Requirements For STOL Navigation Equipment

American Airlines conducted a 75-hour flight test evaluation of the McDonnell Douglas Model 188 (Breguet 941S) STOL aircraft in the spring of 1969. Simulated airline operations were conducted in the St. Louis, Chicago, and New York metropolitan areas. The basic test objective was to investigate the suitability of this type aircraft as a means of providing large scale STOL passenger service between major city centers. The Model 188 is a "propulsive lift" STOL aircraft. It is powered by four, inter-connected turboprop engines, and is controlled through an integrated flight control. system which permits 7-1/2 glide slope approaches, 65 knot IAS approach speeds and high maneuverability at low airspeeds. It has a 58-passenger capacity. A great deal of information was obtained on the aircraft, airborne equipment. and operational procedures. A major portion of the evaluation included extensive onboard navigation equipment testing and data recording to identify the quantitative and qualitative requirements for a suitable STOL navigation system. Three different area/vertical navigation systems (3D RNAV) and one microwave ILS landing system were selected for evaluation. Each system utilized different combinations of signal inputs, different operating principles, and different display methods, as noted in Figure 1.