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4.4 Span Adjust Procedure
1. Connect the pitot-static test equipment to the aircraft=s static line, and
2. Apply power to the altitude digitizer/transponder.
3. Set the primary flight altimeter barometric pressure to 29.92 In. Hg. (1013
4. Interrogate the transponder with the ramp tester, while observing the
5. Increase pressure until the digitizer=s output just makes the transition from
6. Repeat steps (4) and (5) until the "125 foot tolerance is achieved for both
7. Exercise the aircraft=s static system over the operating range of the altitude
8. Verify that the digitizer=s output is disabled when the transponder is not in
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.
connect the transponder test set per the manufacturer=s recommendations.
The digitizer=s two altitude adjustment potentiometers are identified as L
and H, representing low and high altitude. The low adjustment is closest to
the edge of the housing, and the high adjustment is closer to the center of
the housing.
MB).
altitude code, decrease pressure to the point where the altitude code just
makes a transition to the maximum altitude encoded. Verify that the
digitizer is within "125 feet of the altimeter=s reading. If not, adjust the
high potentiometer until the transition point is within 30 feet of the
altimeter reading.
0 feet to -100 feet. Verify that the altimeter reads within "125 feet of the
digitizer. If not, adjust the low potentiometer until the transition point is
within 30 feet of the altimeter reading.
the maximum calibration altitude and the minimum calibration altitude.
digitizer and, with increasing and decreasing pressure, verify at a
minimum of ten test points that the 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.
mode AC@, or when the AAltitude Disable@ switch is in the off position.
-14-
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