A helicopter may be operated at less than the minimums prescribed in paragraph
(2) or (3) of this section, provided each person operating the helicopter complies
with any routes or altitudes specifically prescribed for helicopters by the FAA.
A powered parachute or weight-shift-control aircraft may be operated at less than
the minimums prescribed in paragraph (3) of this section.
Each person operating an aircraft shall maintain the cruising altitude or flight level of
that aircraft, as the case may be, by referring to an altimeter that is set as follows:
1. Below 18,000 feet MSL
The current reported altimeter setting of a station along the route and
within 100 nautical miles of the aircraft.
If there is no station within the area prescribed above, then the current
reported altimeter setting of an appropriate available station.
In the case of an aircraft not equipped with a radio, the elevation of the
departure airport or an appropriate altimeter setting available before
departure is used.
2. At or above 18,000 feet MSL, all altimeters must be set to 29.92 inches.
The lowest usable flight level is determined by the atmospheric pressure in the area of
operation as shown in Table 8-2.
Current altimeter setting
Lowest usable flight level
29.92 (or higher)
29.91 through 29.42
29.41 through 28.92
28.91 through 28.42
28.41 through 27.92
27.91 through 27.42
27.41 through 26.92
Table 8-2 -- Altimeter settings (lowest usable flight level)
To convert minimum altitude prescribed under CFR 91.119 and 91.177 to the minimum
flight level, the pilot shall take the flight level equivalent of the minimum altitude in feet