You are flying a planned track, you pinpoint your position, and you find you are a few miles off. How much should you turn, and which way? The 1 in 60 rule answers that in seconds, without a navigation computer. In this guide you will learn how to use the 1 in 60 rule for the DGCA Air Navigation exam, work out track error and closing angle, and avoid the mistakes that cost easy marks.
What is the 1 in 60 rule?
The 1 in 60 rule says that if you are 1 nautical mile (NM) off track after flying 60 NM, your track is in error by about 1 degree. The same ratio scales up and down: 2 NM off after 60 NM is about 2°, and 1 NM off after 30 NM is also about 2°.
It works because one radian is about 57.3°, and for small angles the angle in radians is almost equal to "distance off divided by distance flown". Rounding 57.3 to 60 makes the arithmetic easy to do in your head, and the small error this adds hardly matters for the angles pilots normally correct.
The general formula is:
Angle (degrees) = (distance off track ÷ distance flown) × 60
Track error and closing angle explained
The two angles you need are track error and closing angle. Together they tell you how far to turn to reach your destination.
- Track error (TKE): the angle between the required track and the track you have actually made good. It is based on the distance gone from your last fix.
- Closing angle (CA): the extra angle needed to converge on the destination from where you are now. It is based on the distance to go.
The formulas are:
TKE = (distance off track × 60) ÷ distance gone
CA = (distance off track × 60) ÷ distance to go
Both angles always use the same "distance off track". Only the distance below the line changes.
Heading correction to regain track
To fly direct to your destination, alter heading by TKE + CA, turning back towards the required track. The track error cancels the drift you were not allowing for, and the closing angle points you at the destination.
If instead you want to rejoin the original track rather than go direct, a common method is:
- Alter heading by double the track error towards the track.
- After flying the same distance you have already flown since the last fix, you should be back on track.
- Then alter heading by one track error back the other way, so the new heading corrects for the drift and keeps you on track.
Both methods assume the wind stays the same. In a real aircraft you then check the next fix and refine.
Worked example: 1 in 60 rule step by step
A leg is 100 NM long on a required track of 090°(T). After 40 NM you fix your position 4 NM right of track. Your heading has been 090°(T).
Distance gone = 40 NM
Distance to go = 100 − 40 = 60 NM
Distance off track = 4 NM (right)
TKE = (4 × 60) ÷ 40 = 6°
CA = (4 × 60) ÷ 60 = 4°
Correction to fly direct = 6° + 4° = 10° left
New heading = 090° − 10° = 080°(T)
You are right of track, so the correction is to the left. As a check, the exact track error here is about 5.7°, so the rule's 6° is close enough for practical flying and for exam answer options.
Using the 1 in 60 rule for descent planning
The same idea helps with vertical navigation. One NM is about 6,076 ft, so a 1° slope drops roughly 6,076 ÷ 60 ≈ 100 ft for every NM flown.
- A 3° glide path is therefore about 300 ft per NM. (The exact figure is close to 318 ft per NM.)
- A common rule of thumb for the rate of descent on a 3° path is groundspeed × 5, in feet per minute. At 120 kt groundspeed that is about 600 ft per minute.
These are quick estimates for planning and cross-checking, not exact answers. If a question gives you a formula or asks for precise values, use what the question asks for.
Common mistakes in DGCA air navigation mental calculations
- Mixing up distance gone and distance to go. TKE uses distance gone; CA uses distance to go.
- Turning the wrong way. If you are right of track, turn left, and the reverse.
- Measuring distance gone from the wrong point. Measure from the last known position (the last fix), not always from the departure point.
- Using the rule for large angles. It becomes less accurate as the angle grows. It is normally treated as reliable up to about 20°.
- Forgetting the double-track-error turn back. After regaining track, you must turn back by one track error, or you will cross the track and drift off the other side.
Track error uses distance gone, closing angle uses distance to go, and the correction to the destination is the sum of both.
Frequently asked questions
What is the 1 in 60 rule in aviation?
The 1 in 60 rule is a navigation rule of thumb: 1 NM off track after 60 NM flown means a track error of about 1 degree. Pilots use it to work out track error, closing angle and heading corrections mentally, without a navigation computer, and it is a regular topic in DGCA Air Navigation.
How do you calculate track error?
Multiply the distance off track by 60, then divide by the distance gone since your last fix. For example, 5 NM off track after 50 NM gives a track error of 6 degrees. The answer tells you how far the track made good differs from the required track you planned.
What is closing angle in navigation?
Closing angle is the additional angle needed to converge on the destination from your present off-track position. Multiply the distance off track by 60 and divide by the distance to go. Add it to the track error to find the total heading change needed to fly directly to the destination.
Is the 1 in 60 rule accurate for large angles?
No. The rule relies on a small-angle approximation, so its error grows as angles increase. It is generally treated as accurate enough up to about 20 degrees. For larger angles, use a navigation computer such as the CRP-5 or trigonometry, especially when an exam question needs a precise answer.
How do you use the 1 in 60 rule for descent?
Because a 1-degree slope loses about 100 ft per nautical mile, a 3-degree glide path is roughly 300 ft per NM. Multiply your groundspeed by 5 to estimate the rate of descent in feet per minute. At 120 knots groundspeed, that gives about 600 ft per minute.
Practise the 1 in 60 rule
The 1 in 60 rule becomes second nature once you have solved a few dozen problems. Test yourself with our free DGCA practice questions, and use the wind triangle solver to see how wind creates the drift that the 1 in 60 rule corrects. Fly with Sudharshan Aviation Academy (FSAA) teaches the 1 in 60 rule alongside every other navigation calculation in the DGCA Air Navigation course, in Bengaluru and online.