DR position is an estimated position of the aircraft
based on initial data (time elapsed, wind direction/velocity, heading,
airspeed) that is used when overflying areas with no radio navigation coverage,
or with no visual checkpoint available.
Positioning in dead reckoning navigation is obtained by adding translation/displacement vectors.
The next new position using the aircraft’s speed and
course being calculated is the DR position. Correcting the DR position for
crosswind, steering error results in an estimated position (EP). INS develops a
very accurate EP. A line joining the last known position and the actual DR
position is an estimated track, which differs from the actual track depending
on the accuracy.
Accuracy of DR position depends on the following factors:
- flight time since last known position update,
- difference between actual and forecasted wind,
- accuracy of the forecasted wind,
- accuracy of heading (steered HDG), airspeed and TAS,
- pilot skill and navigation accuracy flown.
DR technique is also used when operating using RNAV and
the there is no signal received from either VOR or DME. Then the system selects
the DR mode for a short time, based on the last computed values. The RNAV is
trying to update the aircraft’s position based on the current TAS (from Air
Data Computer) and HDG (from compass).
To sum it up, dead reckoning is an algorithm used
to extrapolate entity states, used in modern navigation methods.
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