NORTH AND SOUTH AMERICA - CNATRA - The US Navy

3-60 UNITED STATES
airport on an appropriate altimeter setting available before
departure shall be used.
b. AT AND ABOVE 18,000’ MSL - The standard setting QNE
(29.92” Hg) will be used at all times during flight. When using the
standard altimeter setting, all reference to altitudes shall be made
in Flight Levels. Procedures for determining the lowest usable
Flight Level will be found in the Flight Information Handbook in
Section B, Altimeter Changeover Procedures.
EXAMPLE: FL250 represents a standard pressure differential of
25,000’. In order to assure that the Flight Level is actually at or
above 18,000’ MSL, pilots will not select nor controllers assign
certain Flight Levels when the altimeter setting is below 29.92” Hg.