F-16 database terrain cueing. An investigation of display handling qualities

Database terrain cueing (DBTC) is one of five functions in the new Digital Terrain System (DTS) to be integrated into all F-16s. The terrain-referenced navigation (TRN) function of the DTS determines aircraft position relative to a stored digital flight map based upon terrain elevation data. The DBTC function provides a vertical steering guidance cue displayed as a box in the head-up display. By keeping the flight path marker in this box, a pilot could fly at a preset terrain clearance. The DBTC function demonstrated military utility by serving as a cue to aid the pilot in terrain masking in low visibility. While trying to closely follow the DBTC box, pilots uncovered a pilot induced oscillation (PIO) problem which was more prevalent at high speeds in rough terrain. To analyze this, the test team developed a tracking task. From the evaluation, the team identified three problems; discrete jumps, jitter, and high sensitivity to pilot inputs at high speeds. Through ground simulation, test team engineers came up with potential solutions to these problems. Low update rate error estimates were removed to minimize the occurrence of discrete jumps. A low-pass filter in the vertical acceleration feedback loop was adjusted to reduce jitter. A velocity dependent lag filter was added to the vertical acceleration feedback loop to reduce high-speed sensitivity. The result was a DBTC system which will be an aid instead of a distraction while terrain masking.