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permeability tuning
2 In aerostat, measure of rate at which gas at STP can
pass through fabric, usually expressed in litres per 24 h.
3 In amphibian, ratio of volume of landing-gear
compartments that can be occupied by water to whole
buoyant volume.
permeability tuning Radio tuning by varying permeability
of inductor core, usually with translating bar of
ferrite.
Perminvar Family of low-hysteresis alloys of Fe/Ni/Co.
permissive action link Highly secure, jam-proof data
links (various categories) which enable bomber crew to
trigger nuclear weapon live from cockpit when bomber is
at safe distance (hi-alt laydown only).
permittivity Dielectric constant: relative * is ratio of
electric flux density in medium to that which same force
would produce in vacuum, symbol r , unit farads per
metre; absolute * o is in vacuum, often called free space
(see Coulomb law).
Permit to fly Issued to categories, such as homebuilts,
warbirds, classic GA aircraft and micros, that do not
qualify for a C of A but may be flown with restrictions.
(UK CAA).
Permly Permanently (FAA).
PERP Peak effective radiated power.
perpendicular-heading square Training manoeuvre in
which helicopter is flown around square, crabbing at 90°
sideways along each of the four sides.
persistence A measure of flight endurance, especially
over target area or other hazardous environment.
persistent area-denial Use of loitering robotic systems
[ie, UAVs] to provide non-stop surveillance/attack over
battlefield for period of days to months.
Pervivs Persistremt elevated recon[naissance] surveillance
intelligence unmanned system (USN).
personal equipment connector Quick-make/break multichannel
coupling for aircrew oxygen, R/T, intercom,
g-suit and EC. Not necessarily synonymous with AEA.
Personal Proficiency Index Assessment of pilot experience
and capability, principally prior to qualification on
VLJ (2005–).
personal transprt unit Airlift bed providing intensive
care.
personnel locator beacon Miniature transmitter sending
coded signal and worn on flying clothing.
personnel reaction time Time from nuclear warning to all
defensive measures taken.
Perspex Family of methyl methacrylate plastics
important as aircraft transparent material (ICI).
Pert, PERT Programme Evaluation and Review
Technique; critical path method.
perturbation velocity Difference between local and freestream
velocities, symbol usually V p .
PES 1 Passenger entertainment system, audio plus film.
2 Polyethersulphone.
3 Pre-entry [to inlet] streamline.
Pesa, PESA Passive electronically-scanned antenna.
PESO Product engineering services office.
PET 1 Piston-engine time.
2 Positron emission tomography.
3 Polyethylene terephthalate.
4 Point of equal time.
5 Pacific engineering trials.
PETA, Peta Pulsed-ejector thrust augmentor.
peta Prefix, × 10 15 , symbol P.
PFF
Petal Preliminary Eurocontrol test of air/ground data
link; II adds Phase II, IIe adds Phase II Extension.
petal cowling One divided into large hinged segments
opening like petals of flower.
PETF Practice emergency training frequency.
PETN Pentaerythritol tetranitrate (explosive).
petrol Fuel or solvent tailored from hydrocarbons [eg
heptane, hexane, octane] plus additives. Density
0.708–0.72, giving typical mass 3.93 kg (8.65 lb) gal –1 , 3.27
kg (7.2 lb) US gal –1 , different fractions boil at from 41°C.
US = gasoline, universal name in aviation Avgas. Today
almost all petrol available at airfields is of 100LL grade
(*100-octane, low-lead”), also called F-18 (NATO) or
Avgas 100/130 (UK Joint Service), density about 0.715,
colour blue. Preserved warbirds and a few other aircraft
require Avgas 115/145, NATO F-22, density about 0.708,
colour purple. See low-lead, octane number.
Petroseal A film-forming foam fire-extinguishant.
Pett, PETT Project engineers & technologists for
tomorrow.
petticoat In airship gas duct, pleated sleeve able to seal
duct yet leaving clear passage when released.
Petty valve Operated manually after fighter mission to
release pressure in gun-firing pneumatic circuit (pre-
1950).
PEU Pod, power or processing electronics unit.
PF 1 Pilot flying (others being PNF).
2 Plastics factor.
3 Preformed fragment.
4 See p.f.
PF, P/F 1 Powder forging (or forged).
2 Primary/final talkdown.
P f Pressure in fan duct of turbofan.
pF Picofarad, 10 –12 farad.
p.f. Power factor.
PFA 1 The popular Flying Association [formed 1946 as
ULAA; office, Turweston airfield, NN13 5YD] (UK).
2 Pulverised fuel ash.
3 Porous friction asphalt.
4 Probability of false alarms.
PFAA Professional Flight Attendants Association
(US).
PFB Preliminary flying badge.
PFC 1 Primary flight control, or computer.
2 Powered flight (or flying) control(s).
3 Pre-flight console.
4 Passenger facility charge[s].
5 Porous friction course (see PFA (3)).
5 Protocol functional collection.
PFCES Primary flight-control electronic system.
PFCP Passenger facility charge program (FAA).
PFCS Primary flight-control, or computer, system.
PFCU Powered flying-control unit, surface power unit.
PFD 1 Primary flight display, or director; /ND adds
navigation display, S subsystem.
2 Planned flight data.
3 Personal flotation device.
PFE 1 Purchaser-furnished equipment.
2 Path-following error.
Pfenninger wing Strut-braced, yet high-subsonic wing
with exceptional aspect ratio and reduced thickness,
yielding L/D of up to 40.
PFF 1 Pathfinder Force (RAF, WW2).
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