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within ±30 feet of the nominal transition point. (i.e. while ascending, the digitizer should
transition from 29,900 feet to 30,000 feet at 29,950 feet nominally.)
5. Increase pressure until the digitizer's output just makes the transition from 100 feet to 0 feet.
Verify that the altitude digitizer reports within ±125 feet of the primary flight altimeter. If not,
adjust the low potentiometer until the transition point is within ±30 feet of the nominal transition
point. (i.e. while descending, the digitizer should transition from +100 to 0 feet at +50 feet
nominally.)
6. Repeat steps (4) and (5) until the ±125 foot tolerance is achieved for both the maximum
calibration altitude and the minimum calibration altitude.
7. Exercise the aircraft's static system over the operating range of the altitude digitizer and, with
increasing and decreasing pressure, verify at a minimum of ten test points that the altitude
digitizer and primary flight altimeter correspond within the ±125 foot tolerance. Lightly tap the
altimeter before each reading to eliminate friction. If correspondence is not achieved at any test
point, the altimeter may require calibration.
8. Verify that the digitizer's output is disabled when the transponder is not in mode "C", or when
the "Altitude Disable" switch is in the off position.
CAUTION: Always refer to the altimeter and VSI manufacturer's data for maximum rate of climb or
descent, and any special test conditions which must be complied with.
Page 16 of 57
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