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APPA
4 Association des Pilotes Privés (F).
5 Association of Priest Pilots (US).
6 Autopilot panel.
APPA 1 Associação de Pilotos e Proprietarios de
Aeronaves [ office, São Paulo] (Brazil).
2 Association des Pilotes Privés Avions (F).
apparent precession Apparent tilt of gyro due to rotation
of Earth; vertical component = topple, horizontal = drift.
apparent solar day Length of Earth day determined by
two successive meridian passages of apparent Sun; longer
than sidereal day by time taken by Earth to turn
additional increment to nullify distance travelled in solar
orbit during this day. Basis of most human timescales,
being divided into 24 h, hour being thus defined.
apparent wander Apparent precession.
APPC Advanced program-to-program communications.
APP CON Approach control (FAA).
Apple 1 American pilots participating in local education.
2 Aircraft precise-position location equipment.
Appleton layer F layer (F 1 and F 2 ) of ionosphere, most
useful for reflection of EM radiation (see F-layer).
Appleyard scale Circular slide-rule.
application-specific integrated circuit Self-explanatory,
an ASIC is designed specifically for one application, and
expects to be made by the million in order to play its role
in what may be a giant system. Of course, the same i.c.
may later find other applications.
appliqué Adhesive in the form of thin foils or polymerbased
film, usually on aircraft external surface.
APPP, AP3 Airport Privatization Pilot Program (FAA
from 1996).
APPR Approach.
approach BS.185: ‘To manoeuvre an aircraft into
position relative to the landing area for flattening-out and
alighting’. Now subdivided into various categories, each
of which needs pages of explanation defining circumstances,
clearances and procedure. Following are brief
notes. VFR * may be made with no radio at uncontrolled
airport or airfield. Visual * may be made in IFR by pilot
in contact with runway either not following other traffic
or else in visual contact with it, with ceiling at least 500 ft
above minimum vectoring altitude and visibility at least
three miles. Various types of instrument * are admissible
in IFR with radio TWR authorization: straight-in,
circling, precision (with g/s and runway centreline
guidance) and parallel (two parallel ILS runways, or, in
military aviation, two parallel runways, each with PAR).
In certain circumstances pilot may receive clearance for
contact *, even in IFR. ILS * is most important IFR
precision *. If required and available, pilot can be ‘talked
down’ in GCA or RCA, his only necessary equipment
being primary instruments and operative R/T.
approach area Airspace over designated region of
terminal area controlled by approach control unit (in
some cases serving two or more airfields).
approach beacon 1 Historically, short-range track
beacon (see BABS).
2 Today, beacon giving fix before or after approach
gate (rare).
approach control BS.185: ‘A service established to
provide ATC for those parts of an IFR flight when an
aircraft is arriving at, or departing from, or operating in
approach surveillance radar
the vicinity of, an aerodrome’. DTI (Air Pilot): ‘ATC
service for arriving or departing IFR flights’. FAA adds
‘and, on occasion, VFR aircraft’.
approach control radar ACR, radar at approach control
facility displaying PPI positions (and, in advanced
models, height or alphanumeric data) of all aircraft within
its range (which is not less than radius of furthest point in
the controlled airspace).
approach coupler Electronic linkage between aircraft
ILS receiver and autopilot and hence to AFCS; thus
aircraft can make ‘hands off’ approach.
approach fix From or over which final approach (IFR)
to airport is executed (FAA). On projected centreline 3–5
miles from threshold.
approach glide “A glide preliminary to alighting” (B.S.,
1940).
approach gate Point on final-approach course 1 mile
beyond approach fix (ie further from airport) or 5 miles
from landing threshold, whichever is greater distance
from threshold (FAA).
approach indicator Ambiguous: could mean ILS or
other cockpit instrument or any of several visual systems
on ground indicating angle of approach.
approach lights 1 In modern large airfields, any of
several systems of lights extending along projected centreline
of runway in use towards approaching aircraft to
provide visual indication of runway location, distances,
alignment, glide path slope, and, probably, transverse
horizontal.
2 In smaller or older airfields, one or more lights (often
green) at, or extending from, downwind end of landing
area to show favourable direction of approach.
approach noise Measured on extended runway centreline
1 nm (one nautical mile = 6,080 ft = 1,853 m) from
downwind end of runway, with aircraft at height of 370 ft
(112.58 m). [See Noise].
approach operations Flight operations within approach
area, esp. those of aircraft arriving or departing, designated
as IFR or VFR.
approach plane Approach surface, sloping plane below
which no aircraft should penetrate; in UK ** to grass
airfield extends at inclination of 1:30 in all directions from
periphery of landing area.
approach plate Flight-planning document relevant to
specific airfield, giving details of minimum heights, safe
headings and weather minimums (UK = minima), and
including horizontal map and often also vertical profile
for approach to each instrument runway.
approach power That used on landing approach, often
about 58 percent MTO.
approach power compensator Autothrottle, esp. on
combat aircraft. The APCS [S adds system] was devised
to hold constant AOA (3) during carrier landings.
approach radar See PAR, GCA, SRE.
approach receiver 1 ILS receiver.
2 Historically, radio receiver ‘capable of interpreting
the special indications given by an approach beacon
installation’.
approach sequence Order in which aircraft are placed
while awaiting landing clearance and in subsequent
approach. In busy TMA traffic drawn in blocks from
alternate landing stacks.
approach speed Usually means IAS.
approach surveillance radar Approach control radar.
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