TB 9-4920-457-35
(e) SENSITIVITY pushbutton to HIGH.
(f) Press RESET pushbutton.
(3) Close VERTICAL SPEED control fully.
(4) Open CROSSBLEED CONTROL valve fully. This prevents airspeed indicator
from increasing. Adjust barometric adjustment knob (on front of TI) for 29.92 (1013.3 mb)
indication on barometric indicator.
(5) Slowly open PRESSURE CONTROL valve until pneumatic pressure standard
indicates 0 (zero ft altitude); then close PRESSURE CONTROL valve. If TI altimeter
does not indicate 0 50 ft (30 ft for 55,000 ft altimeters), perform b below.
(6) Slowly open PRESSURE CONTROL valve until TI altimeter indicates -500 ft,
then close. Pneumatic pressure standard will indicate between -450 and -550 ft (-470 and -530 ft
for 55,000 ft altimeters).
(7) Slowly open PRESSURE CONTROL valve until TI altimeter indicates -1000 ft, then
close. Pneumatic pressure standard will indicate between -950 and -1050 ft (-970 and -1030 ft for
55,000 ft altimeters). Record TI error.
(8) Slowly open VACUUM VENT to return system pressure to ambient. Close vent
valve. Record indication on pneumatic pressure standard for hysteresis check.
(9) Slowly open VACUUM CONTROL valve until TI altimeter indicates 500 ft,
then close valve. Pneumatic pressure standard will indicate between 450 and 550 ft (470
and 530 ft for 55,000 ft altimeters). Record TI error.
NOTE
Tap indicator gently to reduce effects of friction.
(10) Repeat technique of (9) above for TI altimeter indications listed in table 4.
Record pneumatic pressure standard indications at 16,000 and 18,000 ft (20,000 and 25,000
ft for 50,000 ft altimeters) for hysteresis check. Also record TI error at each altitude listed
in table 4.
Test instrument
Pneumatic pressure standard indications
indications
(ft)1 2
(ft)
Min
Max
1000
925
(925)
[960]
1075
(1075)
[1040]
1500
1425
(1425)
[1450]
1575
(1575)
[1550]
2000
1900
(1900)
[1940]
2100
(2100)
[2060]
See footnotes at end of table.
6
