Page:NTSB Southern Airways Flight 932 report.pdf/18

 The captain's altimeter (type E42459 10 113, S/N 115) and the first officer's altimeter (type A40179 10 020, S/N 420), both from N97S, were taken to the manufacturer's facility where a detailed teardown was made. The captain's barometric setting counter was determined to be reading approximately 29.67. The synchrotel reading on a servoed angle position indicator was 3.65°. This was calculated to represent an indication of approximately 568 feet; however, the rotor being measured was free to rotate. The outer and inner drums of the assembly, which were held in proper alignment by light spring tension, were displaced so as to indicate an offset of approximately 600 feet. A small area of paint was missing from the drum at an indicated altitude of approximately 1,250 feet. This mark was very similar in size and location to the drum index, bu there was no paint adhering to the underside of the drum index.

The first officer's altimeter was determined to have been set at a barometric setting between 29.73 and 29.24. The displacement from normal alignment between the outer and inner drum was equivalent to approximately 3,000 feet. No impact marks could be found on the altimeter dial, but a portion of the dial next to the drum window revealed an area, similar in shape to the pointer tip, which had been protected from heat damage evident on the surrounding area. The orientation of the protected area indicated that the needle would have to have been either distorted or dislodged prior to the heat damage in order to mask this area of the dial. The masked area was near the outer dial hash mark indicating "3".

A test program was conducted by the Kollsman Instrument Corporation to determine the effect on an altimeter of (1) a 135° roll about the longitudinal axis of the aircraft and (2) sudden stoppage from impact during a rull. The altimeter, mounted on an aluminum bar, 24 inches from the point of rotation, in a standard instrument panel cutout, was set at 875 feet and 29.67. It was rotated about the offset axis at varying speeds from 18°/second to 90°/second. No significant pointer travel was noted due to rotation. Next, the altimeter was allowed to free fall from various heights to a sudden stop. The stop was adjusted to strike the altimeter housing at the rear, midpoint, and panel on successive drops.

The indicated altitude increased to approximately 1,00 feet on each occasion, and was as high as 1,230 feet on one drop from a height of 10 inches. The test was discontinued at this point to avoid damage to the instrument because the estimated shock valves were approximately 50 g's, and the indicated valve compared favorably with that found on the captain's altimeter drum.