Instrumentation

18
Inertial Navigation Systems
Present Position
The aircraft’s present latitude is shown to the
nearest tenth of a minute of arc in the LH
window.
The aircraft’s present longitude is shown to
the nearest tenth of a minute of arc in the RH
window.
The aircraft’s position is therefore shown as
34°31.5’N 117°11.3’W.
Waypoint Positions
The waypoint positions are shown in latitude
(LH window) and longitude (RH window) to
the nearest tenth of a minute of arc.
Figure 18.21 POS (Present position)
In the system which we are considering there
are 10 possible waypoint selections (0 through
9). Waypoints 1 through 9 are simply selected
turning points, and are normally placed into
the system by the operator before the flight.
Waypoint 0 represents the aircraft’s
position at the last time a track change from
present position to a specified waypoint
was selected by the operator.
18 Inertial Navigation Systems
Let us consider briefly how this could be useful.
Suppose that you are half way between, say, Figure 18.22 WPT (Waypoint position)
waypoints 3 and 4 and air traffic control clear
you direct to waypoint 6. By selecting a track
change from waypoint 0 (the aircraft’s present position) to waypoint 6 and inserting it, the
aircraft will fly you directly to Wpt 6 if coupled to the flight director/autopilot.
Figure 18.23 Waypoint Zero
Waypoint zero is reserved for the computer to establish a track from the aircraft’s present
position and will not accept operator entered waypoint co-ordinates.
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