As I Remember It
INU = Inertial Navigator Unit, i.e. LTN-58, as used in triple to feed PP, HDG, GS, etc., to dual Collins AINS-70 RNAV (area navigation system) on National and KSSU varieties of DC10, and dual Ambac RNAV on L-1011. It also provides attitude to the instruments and WX radar.
INS = Inertial Navigation System, containing an INU plus Nav computation, i.e. LTN-51, 72, 92, Delco Carousel IV, and Collins INS-61B. It did the navigation, and fed the instruments and autofright. It was the first self-contained navigation.
IRU = Inertial Reference Unit. Same as INU, only newer and better.
IRS = Internal Revenue Service - the tax collectors in the US.
RNAV = Random and/or Area NAVigation, with inputs from various sensors, optionally including INU/IRU.
FMS = Fright Management System, as first seen on the 767. It added extensive vertical guidance to the lateral guidance for the first time.
3+3T or 2+2T error limit - as decreed by the US Dept. of Defense. All the inertial navigators were capable of much tighter limits, but error was required, especially perhaps for foreign carriers, due to some munitions export control.
GB
Last edited by Graybeard; 2nd Mar 2009 at 22:33.
Reason: typo