The overall errors of the service altimeter installations of a variety of civil transport, military, and general-aviation airplanes have been experimentally determined during normal, landing-approach and take-off operations. The average height above the runway at which the data were obtained was about 280 feet for the landings and about 440 feet for the take-offs.nAn analysis of the data obtained from 196 airplanes during 415 landing approaches and from 70 airplanes during 152 take-offs showed that:n1. The overall error of the altimeter installations in the landing-approach condition had a probable value (50 percent probability) of ±36 feet and a maximum probable value (99.7 percent probability) of ±159 feet with a bias of +10 feet.n2. The overall error in the take-off condition had a probable value of ±47 feet and a maximum probable value of ±207 feet with a bias of -33 feet.n3. The overall errors of the military airplanes were generally larger than those of the civil transports in both the landing-approach and take-off conditions. In the landing-approach condition the probable error and the maximum probable error of the military airplanes were ±43 and ±189 feet, respectively, with a bias of +15 feet, whereas those for the civil transports were ±22 and ±96 feet, respectively, with a bias of +1 foot.n4. The bias values of the error distributions (+10 feet for the landings and -33 feet for the take-offs) appear to represent a measure of the hysteresis characteristics (aftereffect and recovery) and friction of the instrument and the pressure lag of the tubing-instrument system.
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