Probability Distributions of Altitude Deviations

摘要

Aircraft flying at altitudes different from those assigned by Air Traffic Control (ATC), are frequently reported to the Aviation Safety Reporting System (ASRS). This study focuses on the probability distributions of the magnitudes of altitude deviations obtained from 502 ASRS reports received between May, 1978 and November, 1979, and the implications of those distribu- tions. The altitude deviations range from 100 to 16,500 feet, and occur with nearly equal frequencies above and below assigned altitudes. A scatterplot shows that large and small altitude deviations are not strongly associated with high and low altitudes, respectively. The magnitudes of the altitude deviations show marked concentrations at integer multiples of 1,000 feet. Less than 20 percent of this concentration is attributed to rounding. Rather, the concentrations reflect the tendency of deviating aircraft to be flying level at cardinal altitudes or for their deviation to be detected at cardinal altitudes. For approximately 100 reports involving conflicts where avoidance or evasive action was taken, a scatterplot shows that large altitude deviations are not associated with small miss distances. The magnitudes of altitude deviations, without regard to sign, are found to be exponentially distributed with a mean altitude deviation of approximately 1,080 feet. Exponential distributions are also found for various sub-groups of the reports that include: failures-to-maintain assigned altitudes, including premature departures; and failures-to-attain assigned altitudes, including failures to meet crossing restrictions. The exponential distributions of the altitude deviations for these subgroups have mean altitude deviations of 770, 1,240, and 1,960 feet, respectively. Exponential distributions of altitude deviations are also obtained for other subgroups that include: reports involving pilot-initiated and controller-directed evasive actions, reports received from pilots, reports received from controllers, and reports involving military and non-military aircraft.