American Airlines, Inc. and McDonnell Douglas Corp. conducted a 75 hr STOL evaluation in the Spring of 1969. The MDC Model 188 (Br. 941S) test aircraft was equipped with Butler-National, Decca, and Litton 3-D RNAV systems and a Singer-General Precision, Inc. microwave landing guidance system. Data were obtained on the aircraft and STOL/RNAV operational procedures. About 9800 frames of onboard position indications were recorded and correlated with precision, ground-based tracking radar measurements to quantitatively determine the RNAV and TALAR systems' accuracy and repeatability.Results indicate STOL with RNAV is technically feasible and has operational advantages. Conceptually, all of the equipment tested was satisfactory, but neither the test aircraft nor the RNAV systems were satisfactory for airline use in their present form.