TB 9-4920-457-24
(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 for use in step (14).
(8) Slowly open VACUUM VENT to return system pressure to ambient. Close vent
valve. Record indication on pneumatic pressure standard for use in step (13) (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 for use in step (14).
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 use in steps (11) through (13) below (hysteresis check).
Record TI error at each altitude listed in table 4 for use in step (14).
Table 4. Altimeter Accuracy Check
Test instrument
Pneumatic pressure standard indications
(ft)1 2
indications
(ft)
Min
Max
1000
925
(925)
[960]
1075
(1075)
[1040]
1500
1425
(1425)
[1450]
1575
(1575)
[1550]
2000
1900
(1900)
[1940]
2100
(2100)
[2060]
4000
3900
(3900)
[3930]
4100
(4100)
[4070]
5000
4900
(4900)
[4930]
5100
(5100)
[5070]
6000
5900
(5900)
[5930]
6100
(6100)
[6070]
8000
7850
(7825)
[7920]
8150
(8175)
[8080]
10,000
9850
(9825)
[9910]
10,150
(10,175)
[10,090]
12,000
11,800
(11,800)
[11,900]
12,200
(12,200)
[12,100]
14,000
13,800
(13,775)
[13,880]
14,200
(14,225)
[14,120]
3
16,000
15,800
(15,760)
[15,860]
16,200
(16,240)
[16,140]
3
18,000
17,800
(17,725)
[17,840]
18,200
(18,275)
[18,160]
20,0003
19,800
(19,700)
[19,820]
20,200
(20,300)
[20,180]
22,000
21,700
(21,660)
[21,800]
22,300
(22,340)
[22,200]
3
25,000
24,700
(24,625)
[24,760]
25,300
(25,375)
[25,240]
30,000
29,700
(29,550)
[29,740]
30,300
(30,450)
[30,260]
See footnote at end of table.
6
