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direction rounded off to the nearest ten degrees, such as Runway 01 or Runway 25.
runway gradient. The average slope, measured in percent, between two ends or points on a runway.
Runway gradient is depicted on government aerodrome sketches when the total runway gradient exceeds
0.3%.
runway incursion. The act of entering an active runway.
runway temperature. Temperature of the air just above a runway, ideally at engine and/or wing height.
Runway temperature is useful for determining density altitude when computing engine and aircraft
performance.
runway visibility (meteorology). The meteorological visibility along an identified runway, determined
from a specified point on the runway. Runway visibility may be determined by a transmissometer or by an
observer.
rust. A red oxide that forms on ferrous metal (metal that contains iron). Rust has no strength, it is porous,
and it continues to eat the metal until it is completely destroyed. Rust can be prevented by keeping all
oxygen away from the metal, by painting it, or by coating it with a film of oil or grease.
ruthenium. A hard, white, acid-resistant, metallic chemical element. Ruthenium’s symbol is Ru, its atomic
number is 44, and its atomic weight is 101.07. Ruthenium is used as an alloying agent for platinum and
palladium and is also used in the manufacture of electrical contacts.
RVR (Runway Visual Range). An instrumentally derived horizontal distance a pilot should see down the
runway from the approach end. RVR is based on either the sighting of high-intensity runway lights or on
the visual contrast of other objects, whichever yields the greatest visual range.
S
saber saw. An electrically operated, hand-held jigsaw. A saber saw uses a short, stiff blade, motor driven
in a reciprocating (in-and-out) fashion.
sacrificial corrosion. A form of corrosion in which an active material is used as the anode in the corrosion
process to protect a less active material. The anode is sacrificed to save the cathode.
Steel parts are often plated with cadmium to sacrificially protect them from corrosion. If the
coating of cadmium is scratched through to expose the steel, a corrosion cell is formed between the
cadmium and the steel. The cadmium, being more anodic (more chemically active) than the steel, will be
changed into a salt and it, rather than the steel, will corrode.
saddle gusset. A piece of plywood glued to an aircraft structural member. The saddle gusset has a cutout to
hold a backing block or strip tightly against the skin to allow a nailing strip to be used to apply pressure to a
glued joint in the skin.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 500
saddle-mount oil tank (gas turbine engine component). A type of lubricating oil tank used with a gas
turbine engine. A saddle-mount tank is shaped in such a way that it fits around the curvature of the engine
compressor case in much the same way a saddle fits a horse.
SAE (Society of Automotive Engineers). A professional organization that formulates standards for the
automotive and aviation industries.
safety alert (air traffic control). An alert issued by ATC to aircraft under their control if ATC is aware
that the aircraft is at an altitude which, in the controller’s judgment, places it in unsafe proximity to terrain,
obstructions, or other aircraft. The controller may discontinue the issuance of further alerts if the pilot
advises he is taking action to correct the situation or has the other aircraft in sight.
safety belt. A belt installed in an aircraft to hold the occupants tight in their seat. Safety belts are also
called seat belts or lap belts.
safety factor (structural design). The ratio of the maximum load a structure is designed to support, to the
maximum load it will ever be required to support. If a beam is expected to support a maximum load of
10,000 pounds and is designed in such a way that it can support 20,000 pounds, it has a safety factor of
two.
safety gap (magneto ignition system). A location inside a high-tension magneto in which a portion of the
metal housing is close enough to the high-voltage terminal to prevent the secondary voltage building up
high enough to damage the coil insulation. The spark plug normally provides the gap for the spark to jump,
but if a lead is off a spark plug, the secondary voltage could build up high enough to damage the coil
insulation. Rather than the voltage building up this high, it jumps the safety gap.
safety glass. A type of glass that does not leave jagged fragments when it breaks. Safety glass may be made
by laminating a layer of resilient transparent plastic material between two sheets of glass. This type of
safety glass will break, but all of the pieces stick to and are held by the center plastic layer. Another form of
　
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