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AIM

10/12/17

7−2−4

Altimeter Setting Procedures

TBL 7−2−3

ICAO Cold Temperature Error Table

Reported T

emp 

C

Height Above Airport in Feet

200

300

400

500

600

700

800

900

1000 1500 2000 3000 4000 5000

+10

10

10

10

10

20

20

20

20

20

30

40

60

80

90

  0

20

20

30

30

40

40

50

50

60

90

120

170

230

280

−10

20

30

40

50

60

70

80

90

100

150

200

290

390

490

−20

30

50

60

70

90

100

120

130

140

210

280

420

570

710

−30

40

60

80

100

120

140

150

170

190

280

380

570

760

950

−40

50

80

100

120

150

170

190

220

240

360

480

720

970

1210

−50

60

90

120

150

180

210

240

270

300

450

590

890

1190 1500

EXAMPLE−

Temperature−10 degrees Celsius, and the aircraft altitude is 1,000 feet above the airport elevation. The chart shows that

the reported current altimeter setting may place the aircraft as much as 100 feet below the altitude indicated by the altimeter.

7−2−4. High Barometric Pressure

a. Cold, dry air masses may produce barometric

pressures in excess of 31.00 inches of Mercury, and

many altimeters do not have an accurate means of

being adjusted for settings of these levels. When the

altimeter cannot be set to the higher pressure setting,

the aircraft actual altitude will be higher than the

altimeter indicates.

REFERENCE−

AIM, Paragraph 7−2−3 , Altimeter Errors.

b. When the barometric pressure exceeds

31.00 inches, air traffic controllers will issue the

actual altimeter setting, and:

1. En Route/Arrivals. Advise pilots to remain

set on 31.00 inches until reaching the final approach

segment.

2. Departures. Advise pilots to set 31.00 inch-

es prior to reaching any mandatory/crossing altitude

or 1,500 feet, whichever is lower.

c. The altimeter error caused by the high pressure

will be in the opposite direction to the error caused by

the cold temperature.

7−2−5. Low Barometric Pressure
When abnormally low barometric pressure condi-

tions occur (below 28.00), flight operations by

aircraft unable to set the actual altimeter setting are

not recommended.

NOTE−

The true altitude of the aircraft is lower than the indicated

altitude if the pilot is unable to set the actual altimeter

setting.