AIM 8/15/19  7/16/20  TBL 7 − 2 − 2 Lowest Flight Level Correction Factor 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 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). 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. 7 − 2 − 3 Barometric Altimeter Errors and Setting Procedures