background image

AIM

10/12/17

7−2−2

Altimeter Setting Procedures

(f) For aircraft operating IFR and unable to set

the current altimeter setting, the following restric-

tions apply:

(1) To determine the suitability of depar-

ture alternate airports, destination airports, and

destination alternate airports, increase ceiling

requirements by 100 feet and visibility requirements

by 

1

/

4

 statute mile for each 

1

/

10

 of an inch of Hg., or

any portion thereof, over 31.00 inches. These

adjusted values are then applied in accordance with

the requirements of the applicable operating

regulations and operations specifications.

EXAMPLE−

Destination altimeter is 31.28 inches, ILS DH 250 feet

(200−

1

/

2

). When flight planning, add 300−

3

/

4

 to the

weather requirements which would become 500−1

1

/

4

.

(2) On approach, 31.00 inches will remain

set. Decision height (DH) or minimum descent

altitude must be deemed to have been reached when

the published altitude is displayed on the altimeter.

NOTE−

Although visibility is normally the limiting factor on an

approach, pilots should be aware that when reaching DH

the aircraft will be higher than indicated. Using the

example above the aircraft would be approximately

300 feet higher.

(3) These restrictions do not apply to

authorized Category II and III ILS operations nor do

they apply to certificate holders using approved QFE

altimetry systems.

(g) The FAA Regional Flight Standards

Division Manager of the affected area is authorized to

approve temporary waivers to permit emergency

resupply or emergency medical service operation.

b. At or above 18,000 feet MSL. To 29.92 inch-

es of mercury (standard setting). The lowest usable

flight level is determined by the atmospheric pressure

in the area of operation as shown in TBL 7−2−1.

TBL 7−2−1

Lowest Usable Flight Level

Altimeter Setting

(Current Reported)

Lowest Usable

Flight Level

29.92 or higher

180

29.91 to 29.42

185

29.41 to 28.92

190

28.91 to 28.42

195

28.41 to 27.92

200

c. Where the minimum altitude, as prescribed in

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.

TBL 7−2−2

Lowest Flight Level Correction Factor

Altimeter Setting

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

29.42 inches of mercury, the lowest usable flight level will

be 195, which is the flight level equivalent of 19,500 feet

MSL (minimum altitude plus 500 feet).