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AIM

4/20/23

7

2

3

Barometric Altimeter Errors and Setting Procedures

200 feet and visibility 1/2 mile (200

1/2). Subtract 31.00 “Hg. from 31.21 “Hg. to get .21 “Hg. .21 “Hg rounds up to .30 “Hg. Calculate

the increased requirement: 100 feet per 1/10 equates to a 300 feet increase for .30 “Hg. 1/4 statute mile per 1/10 equates to a 3/4 statute
mile increase for .30 “Hg. The destination weather requirement is determined by adding the 300

3/4 increase to 200

1/2. The destination

weather requirement is now 500

1 ¼.

.

[b]

31.00 “Hg. will remain set during the complete instrument approach. The aircraft has arrived at

the DA or minimum descent altitude (MDA) when the published DA or MDA is displayed on the barometric
altimeter.

NOTE

The aircraft will be approximately 300 feet higher than the indicated barometric altitude using this method.

[c]

These restrictions do not apply to authorized Category II/III ILS operations and certificate

holders using approved atmospheric pressure at aerodrome elevation (QFE) altimetry systems.

(7)

The FAA Flight Procedures & Airspace Group, Flight Technologies and Procedures Division may

authorize temporary waivers to permit emergency resupply or emergency medical service operation.

2.

At or above 18,000 feet MSL. All operators will set 29.92 “Hg. (standard setting) in the barometric

altimeter. The lowest usable flight level is determined by the atmospheric pressure in the area of operation as
shown in  TBL 7

2

1. Air Traffic Control (ATC) will assign this flight level.

TBL 7

2

1

Lowest Usable Flight Level

Altimeter Setting

(Current Reported)

Lowest Usable Flight

Level

29.92 or higher

180

29.91 to 28.92

190

28.91 to 27.92

200

3.

When the minimum altitude per 14 CFR Section 91.159 and 14 CFR Section 91.177 is above 18,000 feet

MSL, the lowest usable flight level must be the flight level equivalent of the minimum altitude plus the number
of feet specified in TBL 7

2

2. ATC will accomplish this calculation.

TBL 7

2

2

Lowest Flight Level Correction Factor

Altimeter Factor

Correction Factor

29.92 or higher

None

29.91 to 29.42

500 feet

29.41 to 28.92

1000 feet

28.91 to 28.42

1500 feet

28.41 to 27.92

2000 feet

27.91 to 27.42

2500  feet

EXAMPLE

The minimum safe altitude of a route is 19,000 feet MSL and the altimeter setting is reported between 29.92 and 29.43 “Hg,
the lowest usable flight level will be 195, which is the flight level equivalent of 19,500 feet MSL (minimum altitude
(TBL 7

2

1) plus 500 feet).