release time (air traffic control). A departure time restriction issued to a pilot by ATC (either directly or through an authorized relay) when necessary to separate a departing aircraft from other traffic.
reliability. The ability of an aircraft engine to perform its designed functions under widely varying operating conditions.
relief hole (sheet metal fabrication). A hole drilled at the point at which two bend lines meet in a piece of sheet metal. When a piece of sheet metal is formed into a pan, a square is cut from the corners of the sheet, and the sides are bent upward. The metal where the two bends meet will usually buckle and crack.
To prevent this cracking, a relief hole whose diameter is approximately twice the radius of the bend is drilled at the point the two bends meet. This relief hole spreads the stresses so the metal does not crack.
relief map. A three-dimensional map in which mountains and valleys are formed so they show the way the
land actually looks.

relief tube. A urinal installed in some special-purpose aircraft.

relief valve. A pressure-control valve that relieves any pressure over the amount for which it is set.
Pressure relief valves are used in both hydraulic and pneumatic systems to prevent damaging high pressures
that could be caused by a malfunctioning pressure regulator, or by thermal expansion of fluid trapped in
portions of the system.

reluctance. Opposition to the passage of lines of magnetic flux through a material. Reluctance in a
magnetic circuit compares with resistance in an electrical circuit.

remainder (mathematics). The number left in a mathematical problem when one number is subtracted
from another. The remainder is also the number left in a division problem when the divisor does not go into
the dividend an even number of times.

remanufactured engine. An aircraft engine that has been completely rebuilt by the original engine
manufacturer or by a facility approved by them. A remanufactured engine is considered to be a zero-time

engine and is usually given the same warranty as a new engine.
The term “remanufactured” does not have any official meaning to the FAA, but it is often used to mean the same as the FAA term “rebuilt.” See rebuilt engine.
remote control. Control of an object from a location different from that of the device being controlled. Remote control can be accomplished by fluid power, by electrical current carried through wires, or by signals transmitted by radio or light.
remote scope (radar meteorology). A slave radarscope remotely operated from a weather radar.
Rene metal. The registered trade name for a series of high-strength, high-temperature, nickel-chromium alloys, used in the manufacture of gas turbine engines.
repair. A maintenance procedure in which a damaged component is restored to its original condition or at least to a condition that allows it to fulfill its design function.