reference datum /ref(.)r.ns
de.t.m/ noun a line fixed by the designer from which measurements are made when checking or adjusting wing angles, etc.

reference point /ref(.)r.ns p..nt/
noun a fixed datum near the centre of the airfield landing area
reference signal /ref(.)r.ns s.n(.)l/ noun a signal against which telemetry data signals are compared
refinement /r.fa.nm.nt/ noun an
improvement . An internal locking device is one of the numerous refine-ments to the simple actuator.
reflect /r.flekt/ verb to throw back something such as radio waves or light
. Snow surfaces reflect up to 90% of radiation while rock, sand and concrete reflect only 10–20%.
reflection /r.flek..n/ noun the proc-ess of throwing back of something such as radio waves or light . Glare caused by reflection of sunlight from the top of a layer of fog or haze can seriously reduce the air-to-ground visibility.
reflective /r.flekt.v/ adjective able
to throw back something such as radio waves or light . Reflective power means that at low angles of elevation of the sun, water reflects a great amount of solar radiation thus slowing down the rise in sea surface temperatures.
reflector /r.flekt./ noun a device which throws back something such as light . The shape of a water droplet makes it a good reflector, so water in the atmosphere absorbs and scatters radio waves.
refract /r.frkt/ verb to cause a wave, such as light or sound, to change direction or turn as it passes from one medium into another of different den-
sity . A sky wave starts life as a direct wave and, on reaching the ionosphere, the direct wave is refracted and returns to the Earth’s surface.
refraction /r.frk..n/ noun the
change in direction or turning of a wave, such as light or sound, as it passes from one medium into another of differ-ent density
refrigerant /r.fr.d.r.nt/ noun a
substance to provide cooling either as the working substance of a refrigerator or by direct absorption of heat . Heated air from the main air supply system passes through the evaporator matrix and by induction releases heat into the liquid refrigerant.
refuel /rifju.l/, re-fuel verb to fill with fuel again . Fire risk is always present when you defuel and refuel.
regain /r.e.n/ verb to obtain again or to acquire again . The omni-bearing selector/course deviation indicator is a demand instrument which indicates which way to turn to regain the required bearing.
regard /r.ɑd/ noun a particular point or aspect . in this regard con-cerning this or with reference to this . with regard to concerning or with ref-erence to . With regard to the turbo-propeller engine, changes in propeller speed and pitch have to be taken into account. . verb to look upon or con-sider in a particular way . Thoughtful concern for others is regarded as an essential component of good airman-ship.
regardless /r.ɑdl.s/ preposition
in spite of, despite, with no thought of .