TM 55-4920-231-14
(10) Perform the case leak test on the instru-
CAUTION
ment being tested by turning knob (8, figure 4)
The case leak valve lever must be in
to fully close external case leak valve (10) at
NOR position and the safety valve
40,000 ft. reading on altimeter (3, figure 7). Ob-
closed to isolate the airspeed indicator
serve and time the reading on the altimeter be-
from the vacuum source and prevent
ing tested for excessive leakage. (Refer. to
damage to the instrument.
table 3.)
(5) Place case leak valve lever (3, figure 8)
(11) When case leak test has been com-
in NOR position, case leak valve lever (4) in
pleted, turn knob (8, figure 4) slowly to open
CL position, and turn knob (14, figure 4) to
external case leak valve (10).
close safety valve (13).
(6) Make test hose connections (paragraph
(12) Turn vacuum INCREASE knob (17,
38) and start the tester (paragraph 36).
DECREASE knob (19) to allow instrument
CAUTION
readings to return to normal when the tests have
Do not exceed 3000 fpm while testing
been completed.
altimeters, nor 6000 fpm while testing
(13) Stop the tester (paragraph 37).
rate-of-climb indicators. Exceeding these
limits will damage the instruments.
b. 0 to 80,000 FT. Test.
NOTE
(1) Perform the master instrument tests
Tap altimeter lightIy to remove friction before
(paragraph 39 b).
recording readings at all calibration points.
(2) Set altimeter being tested and altimeter
(7) Turn vacuum INCREASE knob (17,
(3, figure 7) barometric scale (4) at 29.92 with
connection knob (22).
13) and stabilize readings on altimeter (3, fig-
ure 7) by adjusting vacuum DECREASE knob
(3) Place PRESSURE selector knob (10) in
(19).
OFF position and turn knobs (11 and 12) to
(8) Observe reading on instrument being
open valves.
tested at each check point and record on cali-
(4) Turn VACUUM selector knob (20) to
bration card (8, figure 7).
ALT & R.O.C. 0-80,000 FT position and turn
(9) Perform the case leak test on the instru-
knobs (17 and 19) to close valves,
ment being tested by turning knob (8, figure 4)
to fully close external case leak valve (10) at
80,000 ft. reading on altimeter (3, figure 7). Ob-
serve reading on instrument being tested and
time for excessive leakage. (Refer to table 3.)
ALTIMETER
(10) When case leak test has been completed,
STANDARD
INDICATOR
STANDARD
INDICATOR
turn knob (8, figure 4) slowly to open external
ALTITUDE
READING
ALTITuDE
READING
case leak valve (10),
IN FEET
IN FEET
IN FEET
IN FEET
(11) Turn vacuum INCREASE knob (17,
20000
0
500
22000
DECREASE knob (19) to allow instrument read-
1000
25000
ings to return to normal when the tests have
2000
30000
been completed.
4000
35000
(12) Stop the tester (paragraph 37).
40000
6000
c. Negative Altitude.
45000
8000
(1) Perform the master instrument tests
10000
50000
(paragraph 39c).
12000
60000
(2) Set altimeter being tested and altimeter
70000
14000
(3, figure 7) barometric scale (4) at 29.92 with
16000
80000
correction knob (22).
18000
(3) Place VACUUM selector knob (20) in
INSTR. NO.
DATE
OFF position and burn knobs (17 and 19) to
open valves.
AV 001473
(4) Turn PRESSURE selector knob (10) to
NEGATIVE ALTITUDE position and turn
knobs (11 and 12) to close valves.
Figure 13. Altimeter Test Readings.
