Under the 1-in-60 rule, an aircraft 1 nautical mile off track after flying 30 nautical miles has an estimated track error of 2 degrees.

### Why this is right The estimate is displacement divided by distance flown, multiplied by 60. Here, 1 / 30 × 60 equals 2 degrees. ### The concept The 1-in-60 rule is a practical approximation for small navigation angles. The same lateral displacement represents a larger angle over a shorter distance and a smaller angle over a longer distance. The distance used for a track error is the distance already flown, not the distance left to the destination. ### Worked numbers - **Given**: displacement 1 NM; distance flown 30 NM. - **Find**: track error angle. - **Formula**: angle = displacement / distance × 60. - **Solve**: 1 NM / 30 NM × 60 = 2 degrees. - **Answer**: 2 degrees. - **Check**: 30 NM is half of 60 NM, so the same displacement gives twice the 1-degree-per-NM-at-60-NM reference angle. ### Terms - **NM**: Nautical mile, an aviation distance unit. - **Track error**: The angular difference associated with an aircraft's lateral displacement from its planned track. ### Remember A fixed displacement means more angular error when it occurs over less distance.