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6 – i ndex
Transition Level:
The lowest flight level available for useabove the
transition altitude.
TransitionalSurface:
An inclinedplaneassociatedwith the runway
stripand the approach surfaces.
Transponder:
A receiver/transmitterwhichwill generatea reply
signal uponproper interrogation; the interrogationand replybeingon
different frequencies.
UnalertedSee-and-Avoid:
Aprocedurewhereflight crew, whohave
no specific knowledgeof other aircraft in their vicinity, rely solelyon
their ability tophysically sight and avoid collidingwith aircraft that
maybe in their vicinity.
UndershootShear:
Awind shear occurrencewhichproduces an
INITIAL effect of undershooting thedesiredapproachpathand/or
decreasing air speed.
UNICOM (UniversalCommunications):
UNICOM is anon-ATS
communications serviceprovided to enhance the valueof information
normally available about anon-towered aerodrome.
UnserviceableArea:
Aportionof themovement areanot available
for usebyaircraft becauseof thephysical conditionof the surface, or
becauseof anyobstructionon thearea.
Vectoring:
Provisionof navigational guidance to aircraft in the formof
specific headings, basedon theuseof anATS surveillance system.
VFRClimbandDescent:
ATC authorisation for an IFRflight inVMC, at
or below FL180, in classesD andE airspace, to conduct a visual climb
or descent.
VFR-on-Top:
ATC authorisation for an IFRflight tooperate inVMC, at
or below FL180, inClass E airspace at any appropriateVFR altitudeor
flight level (in accordancewithENR 1.2Section 2., ENR 1.7Section 5.
andas restrictedbyATC).
VHFOmni-directionalRadioRange (VOR):
AVHF radio
navigational aidwhichprovides a continuous indicationof bearing
from the selectedVORground station.
definitions