Survival Flying

Dead Reckoning & the Deliberate Offset

With no GPS you do not arrive at a point, you arrive in a cone — widened by every degree you failed to hold and every knot of wind you did not know about. Aim straight at a small field and you reach the road beside it not knowing which way to turn. Aim deliberately to one side and you always know.

Looking straight down · north up

planned track where you might be—

Leg distance120 nmSixty-to-one: one degree of error is one mile off for every sixty flown. Error grows with the leg, so break a long trip into short ones.Heading you actually hold± 3°Not how well you meant to fly it — how well you did, over an hour, hand-flying, with the compass swinging.Wind you didn't know about5 ktThe crosswind your forecast missed. At 100 knots, 10 knots of unexpected drift is about 6° — bigger than most heading errors.Deliberate offset0°Aim to one side on purpose. It has to be bigger than everything above it, or it buys you nothing.

Could be off by

nm, either side

Offset puts you

nm right

Offset costs

nm extra

Which way do you turn?

Arrival

The trade is the whole technique: you give up a couple of miles of flying and a known error you chose, and in exchange you delete a fifty-fifty guess you would otherwise have to make with the fuel running down. It only works if the offset is larger than your uncertainty — and if there is something long beyond the field to run into, so that crossing it means something. Aim off, hit the road, turn the way you already know.