Section 7. Altimeter Settings
2-7-1. CURRENT SETTINGS
a. Current altimeter settings shall be obtained
from direct-reading instruments or directly from
weather reporting stations.
REFERENCE-
FAAO JO 7210.3, Chapter 2, Section 10, Wind/Altimeter Information.
b. If a pilot requests the altimeter setting in
millibars, ask the nearest weather reporting station
for the equivalent millibar setting.
c. USAF/USA. Use the term "Estimated Altimeter" for altimeter settings reported or received as
estimated.
REFERENCE-
FAAO JO 7110.65, Para 3-9-1, Departure Information.
FAAO JO 7110.65, Para 3-10-1, Landing Information.
FAAO JO 7110.65, Para 4-7-10, Approach Information.
2-7-2. ALTIMETER SETTING ISSUANCE
BELOW LOWEST USABLE FL
a. TERMINAL. Identify the source of an altimeter
setting when issued for a location other than the
aircraft's departure or destination airport.
b. EN ROUTE. Identify the source of all altimeter
settings when issued.
PHRASEOLOGY-
THE (facility name) (time of report if more than one hour
old) ALTIMETER (setting).
c. Issue the altimeter setting:
1. To en route aircraft at least one time while
operating in your area of jurisdiction. Issue the setting
for the nearest reporting station along the aircraft's
route of flight:
NOTE-
14 CFR Section 91.121(1) requires that the pilot set his/her
altimeter to the setting of a station along his/her route of
flight within 100 miles of the aircraft if one is available.
However, issuance of the setting of an adjacent station
during periods that a steep gradient exists will serve to
inform the pilot of the difference between the setting he/she
is using and the pressure in the local area and better enable
him/her to choose a more advantageous setting within the
limitations of 14 CFR Section 91.121.
2. TERMINAL. To all departures. Unless specifically requested by the pilot, the altimeter setting
need not be issued to local aircraft operators who have
requested this omission in writing or to scheduled air
carriers.
REFERENCE-
FAAO JO 7110.65, Para 3-9-1, Departure Information.
3. TERMINAL. To arriving aircraft on initial
contact or as soon as possible thereafter. The tower
may omit the altimeter if the aircraft is sequenced or
vectored to the airport by the approach control having
jurisdiction at that facility.
REFERENCE-
FAAO JO 7110.65, Para 4-7-10, Approach Information.
FAAO JO 7110.65, Para 5-10-2, Approach Information.
4. EN ROUTE. For the destination airport to
arriving aircraft, approximately 50 miles from the
destination, if an approach control facility does not
serve the airport.
5. In addition to the altimeter setting provided
on initial contact, issue changes in altimeter setting to
aircraft executing a nonprecision instrument
approach as frequently as practical when the official
weather report includes the remarks "pressure falling
rapidly."
d. If the altimeter setting must be obtained by the
pilot of an arriving aircraft from another source,
instruct the pilot to obtain the altimeter setting from
that source.
NOTE-
1. The destination altimeter setting, whether from a local
or remote source, is the setting upon which the instrument
approach is predicated.
2. Approach charts for many locations specify the source
of altimeter settings as non-FAA facilities, such as
UNICOMs.
e. When issuing clearance to descend below the
lowest usable flight level, advise the pilot of the
altimeter setting of the weather reporting station
nearest the point the aircraft will descend below that
flight level.
f. Department of Defense (DOD) aircraft which
operate on "single altimeter settings" (CFR Exemption 2861A) shall be issued altimeter settings in
accordance with standard procedures while the
aircraft are en route to and from their restricted areas,
MOAs, and ATC assigned airspace areas.
g. When the barometric pressure is greater than
31.00 inches Hg., issue the altimeter setting and:
1. En Route/Arrivals. Advise pilots to remain
set on altimeter 31.00 until reaching final approach
segment.
2. Departures. Advise pilots to set altimeter
31.00 prior to reaching any mandatory/crossing
altitude or 1,500 feet AGL, whichever is lower.
PHRASEOLOGY-
ALTIMETER, THREE ONE TWO FIVE, SET THREE ONE
ZERO ZERO UNTIL REACHING THE FINAL
APPROACH FIX.
or
ALTIMETER, THREE ONE ONE ZERO, SET
THREE ONE ZERO ZERO PRIOR TO REACHING
ONE THOUSAND THREE HUNDRED.
NOTE-
1. Aircraft with Mode C altitude reporting will be
displayed on the controller's radar scope with a uniform
altitude offset above the assigned altitude. With an actual
altimeter of 31.28 inches Hg, the Mode C equipped aircraft
will show 3,300 feet when assigned 3,000 feet. This will
occur unless local directives authorize entering the
altimeter setting 31.00 into the computer system regardless
of the actual barometric pressure.
2. Flight Standards will implement high barometric
pressure procedures by NOTAM defining the geographic
area affected.
3. Airports unable to accurately measure barometric
pressures above 31.00 inches Hg. will report the
barometric pressure as "missing" or "in excess of
31.00 inches of Hg." Flight operations to or from those
airports are restricted to VFR weather conditions.
REFERENCE-
AIM, Para 7-2-2, Procedures.
FAAO JO 7110.65, Para 3-10-1, Landing Information.
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