unserviceable /nsv.s.b(.)l/
adjective not operative . The aircraft cannot be flown because the radio is unserviceable. (NOTE: It is often abbre-viated in spoken English as U (you) S (ess).)
unstick /nst.k/ (informal) verb to
cause an aircraft to take off, or take off in an aircraft . noun a take-off in an air-craft
update /pde.t/ verb to bring up to date, to add the latest information to something . Forecasts are updated and reissued every four hours.
updraft /pdrɑft/ noun US same as
updraught updraught /pdrɑft/ noun a rising current of air . In cumulonimbus clouds, there are updraughts of tremen-dous force. Opposite downdraught (NOTE: It is written updraft in US Eng-lish.)
uplift /pl.ft/ noun the lifting of air by surface features . Thunderstorms are
243 UV
triggered off by convection and/or oro-graphic uplift.
upper /p./ adjective 1. at high alti-tude . upper air . upper winds . In modern meteorological practice, upper air analysis and the construction of contour charts is carried out by compu-
ter. 2. top. Opposite lower . the upper surface of the wing the surface of the wing facing upwards, as opposed to the underside

upper air chart /p. e. t.ɑt/
noun a chart showing airflow pattern and distribution of temperatures at spe-cific altitudes above about 10,000 feet
upper air route /p. e. rut/ noun
a route above FL245, approximately 24,500 ft. Abbreviation UAR upper airspace /p. e.spe.s/
noun the airspace above FL245, approximately 24,500 ft. Abbreviation

UAS upper information region noun
airspace which covers the same geo-graphical area as a flight information region but above 24,500 ft. Abbrevia-tion UIR
upward /pw.d/ adjective moving or directed up . As the aircraft accelerates down the runway, the forces on the wing tips and wing surfaces start reversing direction and instead of being only downward forces of weight, they become upward forces of lift. (NOTE: In US English, upward is used as an adjective and as an adverb.)
upwards /pw.dz/ adverb towards the top . Heat is transferred from the Earth’s surface upwards by convection.
Opposite downwards upwind /pw.nd/ adverb against the wind . The glider was released from the aero-tow 3 miles upwind of the airfield.
Opposite downwind urgency /d.nsi/ noun importance or need for prompt or fast action .
Warnings, cautions and advisory mes-sages are displayed only when neces-sary and are colour coded to communi-cate the urgency of the fault to the flight crew.
USA, US abbreviation United States of
America usable /juz.b(.)l/ adjective capable of being used . On receiving the evacu-ate order, cabin crew must assess if their exits are usable.
usage /jus.d/ noun the act of using something, consumption . Fuel flight planning combines navigation data with fuel usage.