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MAINTENANCE MANUAL
AUTO FLIGHT — INSPECTION / CHECK
1. Air Data Computer Calibration — Check
A. Preparation
SPECIAL TOOLS AND TEST EQUIPMENT
Power supply ............................................................................................................................ 28 Vdc
B. Procedure
NOTE: FAA approval for this test is required and can be granted only if test facility satisfies FAA
requirements for equipment, personnel and documentation to perform tests which meet
qualifications specified in FAR 91.411 and FAR 43, APPENDIX E.
Tests must be performed at about 25°C or temperature compensation must be applied to
test equipment readings. Test equipment must have a high degree of accuracy to permit
hysteresis and after effect testing. It must deliver a steady rate of pressure change to
perform friction tests. Finally, it must be stable to perform case leak and barometric scale
error tests. Sperry ADT-222A, VPT-10 or VPT-30 test set should satisfy these requirements.
When equivalency of pneumatic test set used on aircraft has been approved, the on aircraft
test can be accomplished with checkout procedure.
If repair station elects to perform a bench test instead of an on aircraft test, fabrication of a
test cable for units under test will be necessary.
Sperry Field Engineering will provide assistance to repair stations for construction of
interconnect cables to test air data computer and servoed altimeters. The same procedure
will apply to bench test after units are removed from aircraft and connected to interconnect
cables on test bench.
CAUTION: TO PREVENT FALSE TARGETS ON AIRCRAFT EQUIPPED WITH TCAS, DO
NOT TURN ON TRANSPONDER WITH AIRCRAFT PITOT / STATIC SYSTEM
PUMPED UP UNLESS TRANSPONDER ANTENNA SHIELDS (P/N 7005-8142-
500 OR EQUIVALENT) ARE INSTALLED. KEEP TRANSPONDER ″ON TIME″ TO
A MINIMUM.
(1) Disconnect pitot / static lines from air data computer. Cap these disconnected lines.
(2) Connect pitot / static lines from approved test set to air data computer.
NOTE: If a reverting altimeter (baro-servo) is used on aircraft, static line from test set must
also be connected to altimeter. A simple T-connection will allow connection to reverting
altimeter, air data computer, and test set.
(3) Apply ac and dc power to system under test. When altimeter flag is out of view, set 29.92 HG on
altimeter using BARO SET knob. MB counter should read 1013.
(4) Increase test set altitude as per FAR 43 (Appendix E). Compare altimeter readings with
tolerances specified. Do not exceed 1000 feet per minute during these tests.
NOTE: Test data for this and other tests should be recorded and maintained in test facility
files.
(5) Perform hysteresis tests at 50% and 40% of maximum altitude. Do not exceed 5000 fpm during
these tests.
(6) Perform after effect test.
(7) Perform friction test. Maintain 750 fpm rate for this test.
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MAINTENANCE MANUAL
(8) Reduce altitude to 18,000 feet and perform case leak test.
(9) Perform barometric scale error tests.
(10) Set airspeed and altitude. Press SSEC DISABLE button (if applicable) on front of air data
computer. Read altitude with button pressed. Ensure altitude does not change.
(11) Remove static pressure to present field elevation and reduce airspeed to zero. Disconnect test
set. Uncap and connect pitot / static lines disconnected above.
(12) Perform a system pitot / static leak check per your approved procedures per FAR 43 (Appendix
E).
(13) Install decal, on altimeter and air data computer. This will show units have been tested in
accordance with FAR 91.411. Also, record data of test and other necessary particulars in aircraft
log book.
(14) Record all maintenance actions in accordance with current Federal Aviation Regulations.
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