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Notices to Airmen, or other media, serving the purpose of providing operational flight data essential to safe
and efficient aircraft operations.
national search and rescue plan (air traffic control). An interagency agreement which provides for the
effective utilization of all available facilities in all types of search and rescue missions.
natural aging (metal heat treatment). A step in the heat treatment of aluminum alloys in which the metal
is removed from the quench bath and allowed to gain its full strength at room temperature.
In artificial aging, the metal is held at an elevated temperature for it to gain its full strength in a
shorter period of time.
naturally aspirated engine (reciprocating engine). A reciprocating engine that uses atmospheric pressure
to force the charge of fuel-air mixture into the cylinders. A naturally aspirated engine differs from a
supercharged engine that uses a mechanical air compressor to increase the pressure of the air and force the
fuel-air mixture into the cylinders.
natural numbers. Positive integers (numbers, such as 1, 2, 3, 4, 5, etc.). Natural numbers are also called
counting numbers.
Zero, negative numbers, and fractions are not natural numbers.
nautical mile. A measure of distance used in air and sea navigation. One nautical mile is equal to the
length of one minute of latitude along the earth’s equator. One nautical mile is nominally considered to be
6,080 feet, or 1,853.2 meters. However, when the United States accepted the metric system in 1959, the
nautical mile was officially set as 6,076.115 feet.
nautical twilight. The period of time before sunrise and after sunset when the sun is not more the 12°
below the horizon.
navaids (navigational aids). Any visual or electronic device, airborne or on the surface, which provides
point-to-point guidance information or position data to aircraft in flight.
Electronic navaids have been installed around airports and along airways to help pilots navigate
without reference to visual features of the terrain. Very-high-frequency OmniRange navigation equipment
(VOR), Instrument Landing Systems (ILS), and Distance Measuring Equipment (DME) are examples of
navaids.
navaid classes. Classification of navigational aids according to their operational uses. The three classes are:
T – Terminal, L – Low altitude, and H – High altitude.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 398
navigable airspace. 14 CFR Part 1: “Airspace at and above the minimum flight altitudes prescribed by or
under this chapter, including airspace needed for safe takeoff and landing.”
navigation lights (aircraft). Colored lights on an aircraft used at night to show the direction the aircraft is
moving. A red light is installed on the left wing tip, a green light is on the right wing tip, and a white light
is installed on the tail of the aircraft.
N-channel FET (semiconductor device). A field-effect transistor in which the resistive area between the
source and drain is made of N-type semiconductor material.
NDB (nondirectional beacons). A L/MF or UHF radio beacon transmitting nondirectional signals. The
pilot of an aircraft equipped with direction finding equipment can determine his bearing to or from the
NDB and home on or track to or from the station.
needle and ball indicator (aircraft flight instrument). An old name for a turn and slip indicator. See turn
and slip indicator.
needle bearings. A type of anti-friction bearing. Needle bearings are made of a series of relatively long,
small-diameter rollers (the needles) made of hardened steel. The needles ride between two hardened and
polished steel races. One race is pressed into the housing, and the other race is pressed onto the rotating
shaft. Needle bearings are effective for radial loads only.
needle valve. A fluid control valve that uses a long tapered needle to control the amount of fluid that can
flow through an orifice. The needle valve can be moved into or out of the orifice. When the needle is
completely in the orifice, the fluid flow is minimum, and when it is completely out of the orifice, the flow
is limited by the size of the orifice. When the needle is neither fully in nor fully out, its position controls the
effective size of the orifice and thus the amount of fluid allowed to flow.
“Negative” (air traffic control). A term used by ATC to mean “no,” or “permission not granted,” or “that
is not correct.”
negative (electrical condition). A condition in which there are more electrons (negative charges) than
there are protons (positive charges). A negative condition is indicated by a minus sign (–) in front of the
　
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