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Old 25th Sep 2008, 08:00
  #27 (permalink)  
BOAC
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The FMS does the navigation, the IRS only tells it where it is.
- to be strictly accurate, I think you'll find an 'IRS' merely "tells you which way up you are". Of course, the software etc that control an IRS can easily be adapted to give motion and therefore position information. To give one example, in the 60's the English Electric (BAE) Lightning used a basic inertial platform taken from the Blue Steel ICBM as an 'IRS' which fed the instruments and weapons system computers, but fed TAS from the aircraft ADC into the platform to allow correction for pitch reference as it flew around the globe (not for very long, obviously).

As soon as you add any output from an 'IRS' platform to give "where you are" it becomes an 'INS'.
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