1 in 60 rule
In air navigation, the 1 in 60 rule is a rule of thumb which states that if a pilot has travelled sixty miles then an error in track of one mile is approximately a 1° error in heading, and proportionately more for larger errors. The rule is used by single pilots with many other tasks to perform, often in a basic aircraft without the aid of an autopilot, who need a simple process that can be performed in their heads. This rule is also used by air traffic controllers to quickly determine how much to turn an aircraft for separation purposes.
The rule is based on the small-angle approximation (which states that, for small angles, sin θ ≈ θ, where θ is in radians), along with the fact that one radian is approximately 60°. In reality a 1 mile in 60 error is 0.96°, and the rule becomes increasingly inaccurate for larger errors. But since even a skilled pilot cannot manually fly with better than about 2° accuracy, and winds are constantly varying, the rule remains useful for most realistic situations.
If a pilot is flying a leg of 120 miles and finds after travelling 60 miles that they are two miles to the right of track then a correction of 4° to the left (2° to fly parallel to the intended track and another 2° to bring them to their target) will bring them to their destination.
If a pilot is flying a 120 mile leg and finds after 30 miles that they are two miles left of track then they have flown 4° left of their intended track, i.e.
- 2 × 60/30
left of track. Changing the heading four degrees right will now bring them to parallel the intended track. At that point they still have 90 miles to their next waypoint. They are thus two miles to the left of that and thus the waypoint is 4/3 of a degree (2 × 60/90) to the right or approximately 1° right. The pilot then adds these two to get 5° and flies 5° right of their previous heading.
You can also use the 1 in 60 rule to approximate your distance from a VOR by flying 90 degrees to a radial and timing how long it takes to fly 10 degrees (the limit of the course deviation indicator). The time in seconds divided by 10 is roughly equal to the time in minutes from the station at your current ground speed.