Dead Reckoning

Dead reckoning (DR) is the process of calculating a current position based on a previously known position, elapsed time, speed, and heading — without reference to external position fixes. It is the fundamental navigation technique that underpins all other navigation methods.

The DR Triangle

Dead reckoning depends on three elements working together: the aircraft’s heading (where the nose is pointed), the true airspeed (speed through the air mass), and the wind (which moves the entire air mass over the ground). Combining these three using the navigation triangle gives: track made good (direction of actual movement) and groundspeed (actual speed over the ground).

Error Accumulation

DR errors accumulate over time. Wind forecast errors, heading errors, and airspeed instrument errors all contribute. For this reason, DR position estimates should be updated with actual fixes (GPS, VOR, visual, radar) as frequently as possible. The longer the time since the last fix, the larger the potential DR error.

On the TC Written Exam

DR is fundamental to the navigation section of both PPL and CPL exams. Know how to use the flight computer (or mental arithmetic) to solve wind triangle problems: given track, TAS, and wind, find heading and groundspeed.

Related Terms

See also: Pilotage, Heading, Course, Groundspeed.