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jagged edge. A sharp and irregular edge on a piece of metal, wood, or plastic material.
jam acceleration (gas turbine engine operation). Rapid movement of the power control lever of a gas
turbine engine which calls for maximum acceleration of the engine.
jamming (radar and radio). Electronic or mechanical interference used to disrupt the display of aircraft
on radar or the transmission/reception of radio communications or navigation information.
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jam nut. A thin nut screwed down on top of a regular nut to lock it onto the bolt. The jam nut keeps the
regular nut from backing off. A jam nut is sometimes called a check nut.
JAN specifications (joint Army-Navy). Specifications for technical equipment that have been established
by a joint board of the United States Army and Navy. These specifications describe the equipment in detail.
They are usable for civilian equipment as well as for equipment built specifically for the military.
JATO (jet assisted takeoff). A system of auxiliary thrust used for heavily loaded aircraft to assist their
takeoff. JATO units are small rocket engines fastened to the aircraft structure when a difficult takeoff is to
be made.
The JATO units are fired the moment the aircraft rotates for takeoff, and the boost from the rocket
engines provides the additional thrust needed to get the aircraft airborne. JATO is more properly called
RATO for Rocket Assisted TakeOff.
javelin. The streamlined wood or metal rod that is secured at the intersection of the landing and flying
wires of a biplane. Javelins prevent the wires from vibrating in flight.
jerry can. A flat-sided five-gallon can, used for carrying fuel. Jerry cans are made so they stack together
and fit in special racks on vehicles.
jet (fuel metering system component). A special threaded plug with a specifically designed hole drilled
through it. The diameter and length of the hole and the approach angles to the hole determine the amount of
fuel that can flow through the jet for a given pressure drop across it.
Jet-A fuel (gas turbine engine fuel). A kerosine-type fuel used in most commercially operated
jet-propelled aircraft. Jet-A is similar to military JP-5 fuel. Its flash point is between 110° and 150°F, and
its freezing point is –40°F.
Jet-A1 fuel (gas turbine engine fuel). A kerosine-type fuel similar to Jet-A fuel except that it contains
additives that decrease its freezing point to –58°F. Jet-A1 fuel is used in aircraft that remain at high
altitudes for long periods of time. Jet-A1 fuel is similar to NATO JP-8 fuel.
jet assisted takeoff. See JATO.
Jet-B fuel (gas turbine engine fuel). A gasoline-type fuel used in most military jet-propelled aircraft.
Jet-B fuel has a flash point of 0°F and a freezing point of –76°F. Jet-B fuel is similar to the military JP-4
fuel.
JetCal analyzer (gas turbine engine test equipment). The registered trade name for a piece of test
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equipment used to check the engine RPM and various temperatures and pressures inside an operating gas
turbine engine. A JetCal also checks the accuracy of the instruments installed in the aircraft.
jet fuel. Fuel designed and produced to be used in aircraft gas turbine engines.
jet nozzle (gas turbine engine component). The opening at the rear of the exhaust duct of a gas turbine
engine. A jet nozzle is also called an exhaust nozzle.
jet propulsion. A method of propulsion by thrust produced as a relatively small mass of air is accelerated
through a large change in velocity.
jet pump (aircraft fuel system). A form of fluid pump that produces a low pressure by moving fluid at a
high velocity through a venturi. A jet pump can be used to remove vapor from fuel before it enters a fuel
control unit. Some of the fuel from the main fuel pump is returned to the tank through a venturi (the jet
pump). The venturi is connected to the top of the chamber in which the vapors collect. The low pressure at
the throat of the venturi pulls the vapors out of the chamber and returns them with the fuel back to the tank.
jet pump (environmental control system). A special venturi in a line carrying air from certain areas in an
aircraft that need an augmented flow of air through them. High-velocity compressor bleed air is blown into
the throat of a venturi where it produces a low pressure that pulls air from the area to which it is connected.
Jet pumps are often used in the lines that pull air through galleys and toilet areas.
jet route. A route designated to serve flight operations from 18,000 feet MSL, up to and including flight
　
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