AIP ENR 1.6−1
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
ENR 1.6 [RESERVED]

AIP ENR 1.7−1
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
ENR 1.7 Altimeter Setting Procedures
1. General
1.1The accuracy of aircraft altimeters is subject to
the following factors:
1.1.1Nonstandard temperature of the atmosphere.
1.1.2Nonstandard atmospheric pressure.
1.1.3Aircraft static pressure systems (position
error).
1.1.4Instrument error.
1.2EXTREME CAUTION SHOULD BE
EXERCISED WHEN FLYING IN PROXIMITY TO
OBSTRUCTIONS OR TERRAIN IN LOW
TEMPERATURES AND PRESSURES. This is
especially true in extremely cold temperatures that
cause a large differential between the Standard Day
temperature and actual temperature. This
circumstance can cause serious errors that result in
the aircraft being significantly lower than the
indicated altitude.
NOTE−
Standard temperature at sea level is 15 degrees Celsius
(59degrees Fahrenheit). The temperature gradient from
sea level is minus 2 degrees Celsius (3.6 degrees
Fahrenheit) per 1,000 feet. Pilots should apply corrections
for static pressure systems and/or instruments, if
appreciable errors exist.
1.3The adoption of a standard altimeter setting at the
higher altitudes eliminates station barometer errors,
some altimeter instrument errors, and errors caused
by altimeter settings derived from different geographical
sources.
2. Procedures
2.1The cruising altitude or flight level of aircraft
shall be maintained by reference to an altimeter
which shall be set, when operating:
2.1.1Below 18,000 feet MSL.
2.1.1.1When the barometric pressure is
31.00inches Hg. or less:to the current reported
altimeter setting of a station along the route and
within 100 NM of the aircraft, or if there is no station
within this area, the current reported altimeter setting
of an appropriate available station. When an aircraft
is en route on an instrument flight plan, air traffic
controllers will furnish this information to the pilot at
least once while the aircraft is in the controller’s area
of jurisdiction. In the case of an aircraft not equipped
with a radio, set to the elevation of the departure
airport or use an appropriate altimeter setting
available prior to departure.
2.1.1.2When the barometric pressure exceeds
31.00 inches Hg.:the following procedures will be
placed in effect by NOTAM defining the geographic
area affected:
a)For all aircraft.Set 31.00 inches for enroute
operations below 18,000 feet MSL. Maintain this
setting until beyond the affected area or until reaching
final approach segment. At the beginning of the final
approach segment, the current altimeter setting will
be set, if possible. If not possible, 31.00 inches will
remain set throughout the approach. Aircraft on
departure or missed approach will set 31.00 inches
prior to reaching any mandatory/crossing altitude or
1,500 feet AGL, whichever is lower. (Air traffic
control will issue actual altimeter settings and advise
pilots to set 31.00 inches in their altimeters for
enroute operations below 18,000 feet MSL in
affected areas.)
b)During preflight, barometric altimeters shall be
checked for normal operation to the extent possible.
c)For aircraft with the capability of setting the
current altimeter setting and operating into airports
with the capability of measuring the current altimeter
setting, no additional restrictions apply.
d)For aircraft operating VFR, there are no
additional restrictions; however, extra diligence in
flight planning and in operating in these conditions is
essential.
e)Airports unable to accurately measure barometric
pressures above 31.00 inches of Hg. will report the
barometric pressure as missing" or in excess of
31.00 inches of Hg." Flight operations to and from
those airports are restricted to VFR weather
conditions.
f)For aircraft operating IFR and unable to set the
current altimeter setting, the following restrictions
apply:
1)To determine the suitability of departure
alternate airports, destination airports, and destination
alternate airports, increase ceiling requirements
ENR 1.7−2 AIP
15 MAR 07 United States of America
Nineteenth Edition Federal Aviation Administration
　
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