T-45C TS INav-08
Fuel, Weather, and Alternate Airfield Planning
The primary use of the Wind Side of the Air Navigation Computer is to calculate the forecast ground
speed, which of course is utilized to determine time enroute and fuel required for each leg of the flight.
Another important use is a point-to-point calculation to determine a course and distance from destination
Initial Approach Fix (IAF) to the alternate Initial Approach Fix.
To solve these problems on any model of the circular computer consists of a simple arrangement for
setting up vector triangles.
The Wind Triangle
The wind triangle consists of:
The Wind Vector, made up of wind direction and velocity. Plotted on the wind
side starting at the grommet in the direction of the wind, its length represents
the velocity. On a plotting board it would be a solid line with three
The AIR vector, comprised of the TRUE heading (TH) and the TRUE airspeed (TAS).
The air vector always ends at the beginning of the wind vector (the grommet on the
computer) and represents the path assuming no wind. On a plotting board it would be
depicted as a dashed line, with a single arrowhead.
The GROUND vector is made up of COURSE (CUS) and
GROUND SPEED (GS) and represents the path of the aircraft
caused by the wind. Its origin is the same as the air vector, and
ends at the head of the wind vector (or wind dot). On a plotting
board it would be depicted as a solid line, with a single arrowhead.