Glossary of Terms


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N

Navigation specification

Navigation specification. A set of aircraft and flight crew requirements needed to support performance-based navigation
operations within a defined airspace. There are two kinds of navigation specifications:
Required navigation performance (RNP) specification. A navigation specification based on area navigation that includes
the requirement for performance monitoring and alerting, designated by the prefix RNP, e.g. RNP 4, RNP APCH.
Area navigation (RNAV) specification. A navigation specification based on area navigation that does not include the
requirement for performance monitoring and alerting, designated by the prefix RNAV, e.g. RNAV 5, RNAV 1.


Note.— The Performance-based Navigation (PBN) Manual (Doc 9613), Volume II, contains detailed guidance on
navigation specifications.


NCD

NCD - No cloud detected


NDV

NDV - No directional variation (meteorology)


Near-parallel runways

Near-parallel runways. Non-intersecting runways whose extended centre lines have an angle of convergence/divergence of 15
degrees or less.


Newton

Newton (N). The force which when applied to a body having a mass of 1 kilogram gives it an acceleration of 1 metre per
second squared.


Night

The hours between the end of evening civil twilight and the beginning of morning civil twilight or such other period.


between sunset and sunrise, as may be prescribed by the appropriate authority.
Note.— Civil twilight ends in the evening when the centre of the sun’s disc is 6 degrees below the horizon and begins in the
morning when the centre of the sun’s disc is 6 degrees below the horizon.


Night-Ireland

“night” means the hours between the end of evening civil twilight and the beginning of
morning civil twilight, or such other period between sunset and sunrise as may be specified
by the appropriate authority. In or over the State, “night” shall be deemed to be, during the
period beginning on the 1st day of April, and ending on the 30th day of September, the
time between half an hour after sunset and half an hour before sunrise, and during the
remainder of the year, the time between sunset and sunrise, and for the purpose of this
definition sunset shall be determined at surface level.


NM

Nautical mile (NM). The length equal to 1 852 metres exactly.


Non-instrument runway

Non-instrument runway. A runway intended for the operation of aircraft using visual approach procedures.


Normal operating differential pressure

‘Normal operating differential pressure’ means the pressure differential between the cabin
pressure and the outside ambient pressure, including the tolerances of the normal pressure regulating
system.



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