a. Current altimeter settings shall be obtained from direct reading
instruments or directly from weather reporting stations.
REFERENCE -
FAAO 7210.3, Chapter 2, Section 8, 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 7110.65, Departure Information, paragraph 3-9-1.
FAAO 7110.65, Landing Information, paragraph 3-10-1.
{New-98-3 Revised February 26, 1998}
FAAO 7110.65, Approach Information, paragraph 4-7-11.
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 -
CFR 91.121 (1) requires that the pilot set his altimeter to the setting
of a station along his 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 is using and the pressure in the
local area and better enable him to choose a more advantageous setting
within the limitations of FAR 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 7110.65, Departure Information, paragraph 3-9-1.
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.
{New-98-3 Revised February 26, 1998}
REFERENCE -
FAAO 7110.65, Approach Information, paragraph 4-7-11.
FAAO 7110.65, Approach Information, paragraph 5-10-2.
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.
{New-98-3 Added February 26, 1998}
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" (FAR 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, Procedures, paragraph 7-2-2.
FAAO 7110.65, Landing Information, paragraph 3-10-1.