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visibility prevailing
visibility prevailing Distance at which known fixed
objects can be seen round at least half horizon.
visibility value Distance (see visibility) along runway, in
miles and tenths.
visible horizon Circle around observer where Earth and
sky appear to meet (USAF). Also called natural horizon.
visible light EM radiation to which human eye responds,
typically with wavelength from 400 to 700 mm, 0.4 to
0.7 µ.
visible line Full line on drawing representing a line
visible in assembled subject item.
visible radiation See visible light.
visible spectrum See visible light.
visionics Collective term for optical and electronic
devices, operating at many EM wavelengths, which
enhance human vision, especially at night and in bad
weather or smoke or other adverse conditions.
vision-in-turn window Eyebrow window in roof of flight
deck or cockpit.
visitor Person entering a foreign state for period less
than three months.
Vismir Visible to medium infra-red.
Visol Butyl ether + 15% aniline; rocket fuel with Salbei
(G).
visor 1 Pivoting or translating fairing for forward-facing
cockpit windows of supersonic or hypersonic aircraft, in
latter case with thermal-protection coating.
2 Hinged screen, transparent clear or tinted,
protecting eyes against solar radiation and/or micrometeorites
in space exploration.
Visrep Visual report by reconnaissance pilot.
VISSR Visible IR spin/scan radiometry (or radiometer).
Vis-STAR Vision-based software for track, altitude and
range [or ranging].
Vista 1 Very intelligent surveillance and target
acquisition.
2 Variable-stability inflight-simulator test aircraft.
3 Virtual integrated software testbed for avionics.
4 Visual imagery simulation training aid.
Visual Visual imaging system for approach and landing,
based on a 3.5-µ Flir.
visual See visual contact.
visual acuity Human ability to see clearly, as tested by
letter card.
visual approach Landing approach conducted by visual
reference to surface, esp. by aircraft on IFR flightplan
having received authorization.
visual approach path indicator Simple Vasi for private
pilots with red/amber/green sectors (Lockheed-Georgia).
visual approach slope indicator Systems of visible lights
arranged in pattern at landing end of runway providing
descent (and limited lateral guidance) information. Basic
* comprises downwind and upwind bars each of three
lights on each side of runway (in US, total of 2, 4 or 12),
each light projecting red lower segment and white upper.
When correctly on glidepath, as close as possible to ILS
glidepath, pilot sees pink. For long or LEW aircraft extra
light bars are added in 3-bar *, 3-bar Avasi, T-Vasi and
AT-Vasi. FAA-adopted 1970.
visual arrow Modern equivalent of finger four
(fingertip), too tight for tactical use but common on
recovery to airfield.
visual/aural range See VAR.
visuals
visual contact To catch sight of, or a sudden good view
of, target or Earth’s surface.
visual cue Visual contact of object outside vehicle, esp.
Earth, sufficient to give pilot orientation and position
information; eg first glimpse of ground through cloud
during letdown in remote place far from electronic aids.
visual descent point Optional point on final approach
course of non-precision landing, identified by a navaid,
from which VASI should be visible.
visual envelope Plot of flight-deck window areas
showing range of P1 vision.
Visual Flight Operations Panel Permanently reviews
what is permissible in each class of airspace (ICAO).
visual flight rules Those rules as prescribed by national
authority for visual flight, with corresponding relaxed
requirements for flight instruments, radio etc; in US
typically demands flight visibility not less than 3 st. miles
(1 outside controlled airspace) with specified distances
from any clouds; * on top gives a VFR clearance to an IFR
flight above the weather or cloud.
visual head-up image Imagery created outside simulator,
focused at infinity; alternative or addition to terrain
model or CGI.
visual hold[ing] Over fixed feature easily recognized
from altitude.
visual identification Control (ATC) mode in which
aircraft follows a radar target and is automatically
positioned to allow visual identification (NESN); ie interceptor
pilot looks at other aircraft and, if possible,
identifies type and registration or other identity.
visualization Making fluid flow visible, eg by injection of
carbon tetrachloride or other liquid, smoke, tufting,
schlieren, spark photo, hot wire, china clay on surface,
liquid films etc.
visually coupled Night/all-weather sensor(s) are slaved
to pilot’s helmet-mounted system, so pilot appears to ‘see’
normally (field of regard and FOV impose limitations).
Visually Coupled System Specific system linked with
Tiara, providing monochromatic overlain with aircraft
performance data, on pilot’s HMD.
visual meteorological conditions Generally UK counterpart
to VFR, requiring visibility 5+ miles and 1,000 ft
vertical and 1 n.m. horizontal from any cloud [variations
if a/c below 3,000 ft a.m.s.l.].
visual/optical countermeasures Those directed against
human eyesight, ranging from reduction of night adaptation
to blinding.
visual photometry Luminous intensity judged by eye.
visual range Distance under day conditions at which
apparent contrast between specified target and background
becomes equal to contrast threshold of observer
(there is also night *) (see RVR, RVV).
visual reference Earth’s surface, esp. that clearly identified
and thus giving geographical position as well as
attitude and orientation guidance, used as reference in
controlling flight trajectory, if necessary down to touchdown.
visual report Identical to hot report but based solely on
aircrew observations; answers specific questions
concerning target for which sortie was flown (ASCC).
(ASCC adds ‘not to be confused with inflight report’,
while DoD states ‘not to be used; use inflight report’).
visuals Lifelike scenes viewed through windows of
simulator, almost always wholly synthetic and computer-
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