MTTUR  Mean Time To Unscheduled Removal. A performance figure calculated by dividing the summation of times to unscheduled removal for a sample of removed items by the number of removed items in the sample. This is different from MTBUR since no allowance is given to items that have not been removed. 
MU  ACARS Management Unit 
MULT  Multiplier 
MUS  Minimum Use Specification. A generic description by parameter and characteristics of the test equipment and resources required for testing a unit or system. 
MUX  Multiplexer 
N 
N1  Fan speed 
N2  Intermediate compressor speed 
N3  High speed compressor 
NACA  National Air Carriers Association 
NADIN  National Airspace Data Interchange Network 
NAS  National Airspace System 
NASA  National Aeronautics and Space Administration 
NASPALS  NAS Precision Approach and Landing System 
NAS/TRB  National Academy of Science,Transportation Research Board 
NAT  North Atlantic Region 
NAT SPG  North Atlantic Systems Planning Group 
NATCA  National Association of Air Traffic Controllers 
NATRSSIG  ICAO North Atlantic ReducedSeparation Standard Implementation Group 
NATS  (1) North Atlantic Track System (2) UK National Air Traffic Services 
NAV  Navigation 

NAVAID  Navigational Aid 
Navigation  A medium holding the customized navigation 
Datacard  database. 
NAVSTAR  The NAVSTAR global positioning system (GPS) is a 
system using 24 satellites,all reporting precise time 
signals,along with location keys. Eight satellites are 
in each of three 63-degree inclined plane circular 
orbits at 11,000 nmi in altitude. The system is used 
for navigation and determining exact position. 
Nautical Mile  Equivalent to 6,076.1 feet, or approximately 1.15 
(nmi)  statute miles. 
NBAA  National Business Aircraft Association 
NC  Numerical Control 
N/C  New installation Concept 
NCA  National Command Authority 
NCD  No Computed Data 
NCR  National Cash Register 
NCS  Network Coordination Station 
ND  Navigation Display. An EFIS presentation substituting 
for the horizontal situation indicator (HSI). 
NDB  (1) Non-Directional Radio Beacon. A ground station