Page:NTSB Southern Airways Flight 932 report.pdf/34

 variables as winds aloft and flight recorder accuracy. Any lateral adjustment to the flightpath may change the height of the aircraft above the hilly terrain. The time correlation between the flight recorder and cockpit voice recorder may not be exact and could alter the analysis. The individual delay, anticipation, or approximation in each of the callouts could have some bearing on the tabulation. Finally, there is no way of determining whether those variables which could be involved would offset each other or would be cumulative. However, with respect to the tolerances, the aircraft was apparently flying parallel to a 600-foot contour line at the time of the 1,000 foot callout, and the flightpath would have to be shifted approximately 350 feet horizontally before a difference of 100 feet in the terrain clearance would be indicated on a radio altimeter. The second and third callouts occurred when the flight was near the flat terrain of the riverbed and the flightpath would have to be shifted approximately 700 feet horizontally before the terrain clearance would appear to change 100 feet. When the final callout was made, the flight was crossing perpendicularly to a steep ridge which rises sharply to an elevation of approximately 700 feet on the east bank of the river. The flightpath must be shifted at least 400 feet horizontally before a change of 100 feet would be indicated in the terrain clearance.

Analysis of the tabulation suggests that all but the initial callout of "A thousand feet above the ground..." could have been made with reference to the radio altimeter, but even it was couched in terms generally associated with the radio altimeter. The readings that would derive from subtracting the field elevation from the barometric altimeter reading are consistently above 200 feet low, and assuming that the barometric altimeter was accurate, the first officer would have been reporting different values if he had been using that method. On the other hand, the altitude values derived by reference to the radio altimeter are all within 100 feet of the altitudes reported by the first officer. Moreover, the final exclamation recorded prior to the commencement of the sound of impact ("HUNDRED") accords with the altitude which would have been reflected by the radio altimeter at that time and therefore is further evidence that the first officer may have been using that instrument during the approach.

Southern's training program distinguished between the use of radio