Page:NTSB Aircraft Accident Report, United Airlines Flight 389.pdf/28

 experiments measuring reading time and accuracy with both pilots and non-flying enlisted men. The same instruments were also compared by the pilots in flight, using the questionnaire technique to elicit pilot judgments. The results of the various phases of laboratory research showed that the three-pointer altimeter consistently ranked poorest. The pilot preference in the flight tests was overwhelmingly in favor of one of the other types of altimeter. In all objective measurements taken, the three-pointer altimeter ranked the poorest among the instruments tested. The finding that the three-pointer was poorest proved to be statistically reliable in every study in which tests of statistical significance were applied. In a preceding part of this study the mean exposure tune and number of errors on each altimeter was recorded for the two test groups, one consisting of pilots, and the other of non—pilot enlisted men. In 1080 readings of the four altimeters by 18 pilots the mean exposure time in seconds was 0.80 for the CP, 0.84 for the CDP, 1.38 for the DP, and 2.28 for the 3P. The number of reading errors was 7 for the CP, 14 for the CDP, 26 for the DP, and 80 for the 3P. The same data collected during 420 reading trials using 7 non-pilot enlisted men resulted in mean exposure times of 0.85 for the CP, 0.86 for the CDP, 1.50 for the DP, and 2.93 for the 3P. The number of errors by this group were 5 for the CP, 2 for the CDP, 10 for the DP, and 52 for the 3P. The mean number of errors made on each altimeter for pilots was 0.39 CP, 0.78 CDP, 1.44 DP, and 4.44 3P, and for enlisted men 0.71 CP, 0.29 CDP, 1.43 DP, and 7.43 3P.