Effects of Digital Altimetry on Pilot Workload

A series of VOR-DME landing approaches were flown in the NASA Langley Research Center fixed-base full- workload simulator to evaluate the effects of using a digital altimeter on pilot's scanning behavior and workload. Six pilots executed two sets of landing approaches, using a counter-drum-pointer altimeter (CDPA) on one set and a digital altimeter (DA) on the other set. The DA consisted of five, 7-segment LED digits, 0.28 inches high. Pilot scanning data were collected with Langley's oculometer system. The oculometric data were reduced to dwell percentages, average dwell times, transition matrices, dwell time histograms, and were statistically analyzed. The results showed differences in pilot scanning behavior with the DA versus the CDPA. Although the average dwell time on the DA was slightly shorter, there were more transitions to altitude information with the DA. The average dwell time on the attitude indicator was 0.2 seconds shorter after looking at the CDPA than if the previous look had been on the DA, which seems to indicate that after looking at the DA, the pilots had to think about the digital altitude information. Pilot comments were generally negative toward the DA because of (1) the lack of needle motion cues, (2) the pilot could not form a mental picture of his altitude when using the DA, and (3) the pilot had to perform mental arithmetic to estimate the distance to his assigned altitude.