NIST  National Institute of Standards and Technology 
N-Layer  N is set for any layer name (such as link,network, 
etc.) or for the initial (e.g.N-SDU mean LSDU at the 
link layer). OSI model definition. 
NL  Low Pressure Gas Generator RPM 
NLR  Netherlands National Aerospace Laboratory 
NLT  Not Less Than 
nm  Nautical Mile 
NMI  Nautical Mile 
NMOS  N-type Metal Oxide Semiconductor 
NMT  Not More Than 
NOAA  National Oceanic and Atmospheric Administration 
NOC  Notice Of Change 
NO COM  No Communication. A NO COM annunciation indi-
cates that a downlink message has not been acknowl-
edged in an ACARS system. 
Noise  Undesired random electromagnetic disturbances or 
spurious signals which are not part of the transmitted 
or received signal. 
NOTAM  Notice to Airmen 
NPA  Non-Precision Approach 
NPDU  Network Protocol Data Unit 
NPRM  Notice of Public Rule Making 
NRP  National Route Program 
NRZ  Non-Return to Zero 
NSEU  Neutron Single Event Upset 
NSSL  National Severe Storms Laborator y 
NTF  No Trouble Found (referring to testing or checkout of 
unit/module) 
NTSB  National Transportation Safety Board 
NVM  Non-Volatile Memory 

NWA  Northwest Airlines 
NWS  National Weather Service. The NWS provides a ground-based weather radar network throughout the United States. The radar network operates continu-ously and transmits the data to the National Meteorological Center, where it correlates with other weather observations. 
O 
OAC  Oceanic Area Control Center 
OAG  Official Airline Guide 
OAT  (1) Optional Auxiliary Terminal. The OAT may be in the form of a CRT/Keyboard device capable of inter-facing with other sources of data on the aircraft and supplying data to a hard copy printer. (Used in an ACARS system.) (2) Outside Air Temperature. The uncorrected reading of the outside temperature gauge. Different types of gauges require different correction factors to obtain static air temperature.