You planned a leg due east. Thirty nautical miles out, a pinpoint fix puts you 3 nm left of track. How much do you turn to get back? The 1-in-60 rule lets you answer that in your head — no E6B, no calculator.
What the rule says
At a range of 60 nautical miles, 1 nm of lateral displacement subtends an angle of 1°. In other words:
angle (°) ≈ (distance off ÷ distance along) × 60
It's a small-angle approximation, not a physical law — but inside 30° or so it's accurate to within a few tenths of a degree.
Why it works
For a small angle θ in radians, tan θ ≈ θ. One radian is 180 / π ≈ 57.3°, which is just a whisker under 60°. So if a right triangle has
an opposite side of 1 nm and an adjacent side of 60 nm, the
angle at the far vertex is:
- exactly
atan(1 / 60) = 0.9549° - the 1-in-60 approximation gives
(1 / 60) × 60 = 1°
An error of 0.045° at 60 nm — nothing in cockpit arithmetic.
The approximation holds well up to about 20°–25°. At 30° it's off by about 6% (reading 30° where the true angle is 26.6°). That's the edge of its useful range.
Three ways to use it
1. Track Error Angle — how far off the planned track are you?
You've flown the planned heading for some distance and pinpointed your position. The angle between the planned track and your actual ground track is the Track Error Angle (TEA):
TEA = (distance off-track ÷ distance gone) × 60
A TEA of 6° means you're crabbing 6° away from the planned track. If you simply turn your heading by 6° in the opposite direction and hold it, you'll fly parallel to the planned track — you won't regain it, but you'll stop getting further off.
2. Closing Angle — how much more would you need to hit the next waypoint?
Knowing your current off-track distance and the range still to go, the angle you'd need to turn just to reach the next waypoint is the Closing Angle (CA):
CA = (distance off-track ÷ distance to go) × 60
3. Combined correction — back on track at the waypoint
To both stop the drift and intercept the track at the next waypoint:
Total correction = TEA + CA
Apply this correction in the direction that brings you back to track. You'll fly a new constant heading and pass over the waypoint exactly on the planned track.
Worked example
You're flying a 120 nm leg from A to B on a planned track of 090°. After 40 nm a fix puts you 4 nm south (right of track — planned track is due east). Distance to go to B is 80 nm.
Track Error Angle:
TEA = (4 ÷ 40) × 60 = 0.1 × 60 = 6°
Your ground track is 6° south of planned. A 6° turn left (to 084°) would make your new heading parallel to the planned track.
Closing Angle:
CA = (4 ÷ 80) × 60 = 0.05 × 60 = 3°
A further 3° left turn is needed to converge on B.
Combined correction:
Total = TEA + CA = 6° + 3° = 9°
New heading = 090° − 9° = 081°. Hold it and you'll cross B on track.
Common mistakes
- Forgetting to add TEA and CA. Correcting by TEA alone flies parallel to the planned track — you'll miss the waypoint by the same distance you were off when you started correcting.
- Using the rule at long range. At 200 nm with 10 nm off-track, the rule gives 3°, but the true angle is 2.86° — fine. At 60 nm with 30 nm off, the rule gives 30° where the truth is 26.6° — now you're chasing a bad number. Above ~25° the approximation breaks down.
- Sign errors. If the drift is to the right of track, the correction is to the left, and vice versa. Work out the direction first, do the arithmetic second.
- Measuring off-track parallel to the planned track. The formula uses the perpendicular distance from your actual position to the planned track line. If you read off-track as a diagonal, the math is wrong.
Why it matters
The 1-in-60 rule is the single most-used piece of mental nav arithmetic in dead-reckoning flying. It shows up repeatedly on ATPL General Navigation papers — often hidden inside chart questions as "how much should the pilot alter heading to reach the next waypoint" — and it's the backstop when GPS drops off and you're back to map, clock, and compass.