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On a typical Navigation Display (ND) the current in-flight Wind Velocity (W/V) is displayed. Where is the W/V information derived from?
  • A
    It is uploaded by data link from the latest available meteorological forecasts.
  • B
    It is determined by the FMC from inputs of heading, drift, True Airspeed (TAS) and ground speed.
  • C
    It is manually entered by the pilots, based on the latest information available.
  • D
    It is entered into the FMC by either the pilots or dispatch/operations.

Navigation Display (ND) shows ‘instant’ wind velocity based upon on board computations are now quite accurate when instant variation is not required.
Updating of on-board readouts of wind velocity depends on the system which generates them.
FMS wind is the most accurate, because it is based upon changes of GPS or DME/DME position, but it may only be re-calculated every 30 seconds.

The FMC (Flight Management Computer) is the box that calculates the wind.
The inputs are:
Track, heading and groundspeed from the nav system (varies between models, but typically inertial with updates from GPS and terrestrial navaids); and TAS from the ADC (Air Data Computer)

The FMS solves for the final side of the vector triangle and computes wind (side 1- HDG/TAS; side 2- TRK/GS; side 3- Wind direction/magnitude). In a perfect world, the difference between TRK/GS and HDG/TAS is actual wind (direction, magnitude).

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