Ames Research Center is engaged in an extensive effort aimed at furthering aircraft navigation technology, and investigating the feasibility of advanced concepts, with emphasis on operations in the terminal area. The principal objective of the present effort was to investigate the performance of an aided inertial system based on a Kalman estimator designed to provide accurate real time estimates of the vehicle position and velocity in a runway centered coordinate system. An analytical and digital simulation study was first conducted to refine the system concept. The resulting system concept was then mechanizedin an airborne digital computer using a commercial INS and other NAVAID sensor systems. An inflight evaluation of the system performance was made by flying a CV-340 aircraft in an instrumented test area of the White Sands Missile Range (WSHR). During the flight tests a large volume of data was recorded onboard the aircraft during a series of takeoffs, approaches, fly-bys, and landings. The inflight data included: (1) accelerometer delta-velocities from the platform of the INS, plus attitude and other standard INS data; (2) three ranges from the Ames-Cubic Precision Ranging system and three ranges and range rates from the Motorola AROD system; (3) radar and barometric altimeter measurements; and, (4) a variety of other measurements. The main thrust of this paper is to illustrate the performance obtainable by combining range measurements and other NAVAID data with INS delta-velocity data in a Kalman filter specially designed to operate on the SDS 920 computer which is onboard the CV-340. Results shown include comparisons of Kalman filter estimates with the WSMR cinetheodolite data for the following conditions: (1) system initialization from measured data; (2) real time operation at a reasonable data rate; and, (3) operation under adverse conditions such as measured data with unmodeled error sources and bad data. The method of system evaluation employed was post-flight processing of the recorded data, using a special laboratory mode of the real time onboard filter.