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lethal envelope
mainly with controlled adoption of successively lower
flight levels rather than with the landing; thus * procedure.
lethal envelope Volume, often spherical, within which
parameters can be met for successful employment of
particular munition.
letter boxing Becoming squeezed between cloud layer
and rising ground.
letter-box inlet Large semi-rectangular air inlet along
part of wing (or other) leading edge.
letter-box slot Fixed slot at about 8% chord, usually
ahead of aileron; further aft than slot formed by open slat.
letter of intent Formal letter serving as notice by
customer of intention to purchase, before negotiation of
contract.
LEU Leading edge up (surface angular movement).
leurre Decoy [lure] (F).
l e v Tip chord of vertical tail.
levanter Strong easterly wind [straits of Gibraltar].
Leveche Pronounced. ‘levetchay’, hot, dry S wind
[Spain].
level Air intercept code: “Contact is at your angels”.
level bust Failure by dangerous margin [usually ± 300 ft]
to fly at assigned FL.
level landing Tail-up landing by tailwheel aeroplane;
also known as a wheeler.
levelling circuit AC filter circuit used to smooth out variation
in bias voltage.
level of escape Base of exosphere at which upwardmoving
particle has probability 1/e of colliding with
another on way out of atmosphere.
level off To pull out of dive or gentle let-down and hold
height constant.
levels of similarity Quantified lists of differences in aerodynamics
and systems between early prototypes.
leverage 1 Ratio between variables (eg, if ∆ DOC due to
∆ sfc is 8 times the cost of engines and spares to achieve ∆
sfc then * of improved sfc is 8).
2 Ratio of effect of destroying target to its own intrinsic
value.
leveraged lease Lease of aircraft on any of several forms
of sliding scale.
levered suspension Landing gear wheel(s) carried on arm
pivoted to bottom of leg such that vertical travel of wheel
is greater than that of shock strut.
LEVL Leading-edge vortex lift.
LEW Large eye/wheel distance, ie pilot must allow for
his height above wheels at touchdown.
Lewis NASA research centre for aeronautics,
Cleveland, Ohio, Abb. LeRC.
Lewis aerial Othogonal radar scanning sawtooth profile
generated by electromechanical means to give flapping
beams.
Lewis number Le = Pr (Prandtl)/Sc (Schmidt), used in
hypersonics.
LEWK Loitering electronic-warfare killer (UAV).
LEWP Line echo wave pattern.
LEX Leading-edge extension (US terminology).
Lexan Commercially produced polycarbonate plastic,
usually transparent.
LF 1 Load factor (structural).
2 Load factor (traffic).
3 Local forces, or landing force.
4 Launch facility.
LGI
l.f., LF Low frequency (see Appendix 2).
l F Moment arm of fin [vertical stabilizer], from c.p. to
aircraft c.g.
L + F Leather and fabric.
LFA 1 Landing fuel allowance.
2 Low, or local, flying area.
3 Luftfahrtforschungsanstalt (G).
4 Low-frequency active.
5 Lawyers’ Flying Association [office London], (UK).
LFAC Ligne Française d’Aéronefs de Collection
[aircraft preservation; office, F-75116 Paris] (F).
LFADS Low-frequency active dipping sonar.
LFAS Low-frequency active sonar.
LFATS Low-frequency active towed sonar.
LFB Lie-flat bed [seat conversion].
LFBB Liquid-fuel flyback booster.
LFC 1 Laminar flow control (see BLC).
2 Longitudinal friction coefficient.
3 Level of free convection.
LFD 1 Lamp failure detector.
2 Large freight door.
LfE Learning from experience.
LFH Lunar far horizon.
LFI Light tactical fighter (R).
LFICS Landing force integrated communications
system.
LFL Lower flammability limit.
LFM 1 Low-powered fan marker.
2 Laminated, or limited, fine mesh [weather model].
3 Low-powered frequency modulation.
LFP Loaded flank pitch (fir-tree blade root).
LFR 1 Local flight regulations.
2 Low/medium-frequency radio range.
LFRED Liquid-fuelled ramjet engine development.
LFRJ Liquid-fuelled ramjet (in solid rocket case).
LFR, LFRR Low-frequency radio range.
LFS Low-flying system (UK military).
LFSMS Logistic force-structure management
system(s).
LFT Live-fire testing.
LF 2 Liquid fluorine rocket propellant.
LFV Luftfartsverket = navigation services provider
(Sweden).
LFW 1 Linear friction welding.
2 Large-footprint weapon.
LFX Limited-output full-area automatic extraction.
LG 1 Landing gear; also, for F-22, * trainer (ground
support item).
2 Laser gyro.
3 Landing ground.
4 Lehrgeschwader, instructional group (G).
L G Landing-gear wheelbase.
LGA 1 Low-gain antenna.
2 Local Government Association [office, London, has
two aviation groups] (UK).
LGB Laser-guided bomb.
LGCIU Landing-gear control and interface unit; typically
controls LG and doors, monitors cargo door locks,
senses flap/slat position and interfaces with ECAM, MRS
and BITE (Dowty).
LGDM Laser-guided dispenser munition.
LGE speed Speed at which landing gear may be
extended. See landing gear.
LGI Laser glide slope indicator.
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