off-idle mixture (aircraft fuel metering system adjustment). The fuel-air mixture ratio produced by a
fuel metering system during the time the engine is transitioning from its idle RPM to a speed at which fuel is metered through the main metering system.
off-route obstruction clearance altitude (air traffic control). An off-route altitude which provides obstruction clearance with a 1,000-foot buffer in nonmountainous terrain areas and a 2,000-foot buffer in designated mountainous areas within the United States. This altitude may not provide signal coverage from ground-based navigational aids, air traffic control radar, or communications coverage.
off-route vector (air traffic control). A vector by ATC which takes an aircraft off a previously assigned route. Altitudes assigned by ATC during such vectors provide required obstacle clearance.
offset parallel runways. Staggered runways having center lines which are parallel.
offset rivet set (sheet-metalworking tool). A rivet set, used in a pneumatic rivet gun, in which the cup that fits the manufactured head of the rivet is offset from the center line of the rivet set shank. Offset rivet sets are used to drive rivets in a location where a straight set cannot be used.
offset screwdriver. A screwdriver whose blade is perpendicular to the handle. Offset screwdrivers are used to turn screws where there is not enough clearance to allow the use of a regular screwdriver.
offset throw (crankshaft design). Crank arms on a reciprocating engine crankshaft. The arms, or throws, to which the connecting rods and pistons are attached are offset from the center of the crankshaft to move the pistons in and out of the cylinder. The amount of the offset determines the stroke of the engine.
off-the-shelf item. A standard production item. An off-the-shelf computer program, for example, is a standard program that can be bought and used, rather than having a custom program written.
OFZ (obstacle free zone) (air traffic control). A three dimensional volume of airspace which provides protection for the transition of aircraft to and from the runway. The OFZ clearing standard precludes taxiing and parked airplanes and object penetrations, except for frangible navaid locations that are fixed by function. Additionally, vehicles, equipment, and personnel may be authorized by air traffic control to enter the area using the provisions of FAA Order 7110.65, Air Traffic Control, paragraph 3-1-5. The runway OFZ, and where applicable, the inner-approach OFZ and the inner-transitional OFZ, comprise the OFZ.
ohm (Ω). The standard unit of electrical resistance. One ohm is the resistance of a column of mercury weighing 14.4521 grams, formed into a column of uniform cross section and a length of 1,006.3 centimeters. This standard resistance is measured with the mercury having a temperature of 0°C. More practically, one ohm is the amount of resistance that will cause a voltage drop of one volt when one ampere of current flows through it.