(See ULTRAHIGH FREQUENCY.)
ULTRAHIGH FREQUENCY- The frequency band
between 300 and 3,000 MHz. The bank of radio
frequencies used for military air/ground voice
communications. In some instances this may go as
low as 225 MHz and still be referred to as UHF.
ULTRALIGHT VEHICLE- A single-occupant
aeronautical vehicle operated for sport or recreational
purposes which does not require FAA registration, an
airworthiness certificate, nor pilot certification.
Operation of an ultralight vehicle in certain airspace
requires authorization from ATC
(Refer to 14 CFR Part 103.)
UNABLE- Indicates inability to comply with a
specific instruction, request, or clearance.
UNASSOCIATED- A radar target that does not
display a data block with flight identification and
UNDER THE HOOD- Indicates that the pilot is
using a hood to restrict visibility outside the cockpit
while simulating instrument flight. An appropriately
rated pilot is required in the other control seat while
this operation is being conducted.
(Refer to 14 CFR Part 91.)
UNFROZEN- The Scheduled Time of Arrival (STA)
tags, which are still being rescheduled by the time
based flow management (TBFM) calculations. The
aircraft will remain unfrozen until the time the
corresponding estimated time of arrival (ETA) tag
passes the preset freeze horizon for that aircraft's
stream class. At this point the automatic rescheduling
will stop, and the STA becomes "frozen."
UNICOM- A nongovernment communication facil-
ity which may provide airport information at certain
airports. Locations and frequencies of UNICOMs are
shown on aeronautical charts and publications.
(See CHART SUPPLEMENT U.S.)
(Refer to AIM.)
UNMANNED AIRCRAFT (UA) - A device used or
intended to be used for flight that has no onboard
pilot. This device can be any type of airplane,
helicopter, airship, or powered-lift aircraft.
Unmanned free balloons, moored balloons, tethered
aircraft, gliders, and unmanned rockets are not
considered to be a UA.
UNMANNED AIRCRAFT SYSTEM (UAS)- An
unmanned aircraft and its associated elements related
to safe operations, which may include control
stations (ground, ship, or air based), control links,
support equipment, payloads, flight termination
systems, and launch/recovery equipment. It consists
of three elements: unmanned aircraft, control station,
and data link.
UNPUBLISHED ROUTE- A route for which no
minimum altitude is published or charted for pilot
use. It may include a direct route between NAVAIDs,
a radial, a radar vector, or a final approach course
beyond the segments of an instrument approach
(See PUBLISHED ROUTE.)
UNRELIABLE (GPS/WAAS)- An advisory to
pilots indicating the expected level of service of the
GPS and/or WAAS may not be available. Pilots must
then determine the adequacy of the signal for desired
(See TRAFFIC PATTERN.)
URGENCY- A condition of being concerned about
safety and of requiring timely but not immediate
assistance; a potential distress condition.
(See ICAO term URGENCY.)
URGENCY [ICAO]- A condition concerning the
safety of an aircraft or other vehicle, or of person on
board or in sight, but which does not require
(See ARMY AVIATION FLIGHT INFORMATION