Tip: to find a specific term, use the Acrobat search : click N on the binocular icon in the window bar menu
Nominal Routes Overlap (MTCD) Two aircraft are involved in a nominal routes overlap (MTCD) if the distance between the nominal position of one aircraft at a certain moment in time, and the nominal position of the other aircraft at the same moment, will be less than the required separation criteria (MTCD). Nominal Routes Overlap Data (MTCD) It consists of: system trajectory identifications (2 aircraft); time of first infringement of separation criteria (MTCD) between aircraft nominal positions, plus nominal positions of both aircraft at this time. Non Conformance Warning A message sent to a sector suite that serves to warn controllers of actual or anticipated deviations from the system trajectory. Non Precision Approach A standard instrument approach procedure in which no electronic glide slope is provided (e.g. VOR, TACAN, Loran-C, or NDB). Non-Aircraft Segment See Total System
That portion of the total system located external to the aircraft and includes elements on the ground and/or in space.
Non-Directional Beacon A medium-frequency navigational aid which transmits non-directional signals, superimposed with a Morse code identifier and received by an aircraft's automatic direction finder.
Non-Radar Control Provision of air traffic control service based on aircraft position information derived from sources other than radar. Non-Radar Separation The separation used when aircraft position information is derived from sources other than radar. Non-Validated Mode A See Validation bit.
The Mode A validation bit is FALSE. Non-Validated Mode C See Validation bit.
The Mode C validation bit is FALSE. Norm-Reference Test An instrument to cumulate findings form a number of validity studies to estimate the validity of the procedure for the kinds of jobs or groups of job and settings included in the studies. (SIOP, 1987). Norms 1- Statistics or tabular data that summarise the test performance of specified groups (e.g. test takers throughout the country) (SIOP, 1987).
2- A norm is a standard of achievement in tests or questionnaires usually derived from the average achievement of a large group of individuals. The interpretation of results in tests or questionnaires is normally based on a comparison of the individuals response with those previously obtained to establish the appropriate standard for the test scores.
North American Region
See ICAO Region.

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North American Route System
A system which provides for an air traffic interface between the North Atlantic (NAT) oceanic and domestic airspace in order to organise the fluctuating and reversing traffic flows in the most efficient manner, consistent with the needs of the Aircraft Operators and Air Traffic Services. The system expedites flight planning and reduces the complexity of route clearances thereby minimising the confusion and error potential inherent in lengthy transmissions and readbacks.