4/20/23
AIM
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
1. Air Traffic Control (ATC) will assign this flight level.
TBL 7
−
2
−
1
Lowest Usable Flight Level
Altimeter Setting
Lowest Usable Flight
(Current Reported)
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. 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
1) plus 500 feet).
Barometric Altimeter Errors and Setting Procedures
7
−
2
−
3