Calculators › Separation calculator
ATC separation calculator
Will two aircraft keep their separation? See the closing speed, the closest point and how long you have.
Conflict check
Assumes both aircraft hold their track and groundspeed. Try an example:
In-trail time and distance
Type a distance or a time, and the other follows.
Spacing with speed control
How long a speed difference takes to build or close a gap between aircraft on the same track.
How it works
The calculator treats each aircraft as moving in a straight line at a steady groundspeed and works out how the distance between them changes. Closing speed is how fast that distance is falling right now. It equals the two speeds added together when they’re head-on, and the difference between them when one follows the other. For aircraft on crossing tracks it falls in between, and it changes as they pass.
The closest point of approach is the moment they’re nearest. If that’s less than the minimum you set, the calculator also tells you when the minimum is reached, which is how long you have to act.
Separation minimums
Radar separation is commonly 3 NM in a terminal area and 5 NM en route, with 1,000 ft vertically up to FL410. The real figure depends on the airspace and the radar, and wake turbulence can require more behind a heavier aircraft. This calculator only looks at horizontal distance: aircraft 1,000 ft apart are separated even if their paths cross.
Why groundspeed?
Separation is measured over the ground, so wind matters. Use groundspeed rather than indicated or true airspeed. The speed converter can work it out from IAS, altitude and wind.
Time and distance
Distance in trail is groundspeed × time: at 240 kt an aircraft covers 4 NM a minute, so a 2-minute gap is 8 NM. When a stream slows on approach, the leader slows first and the time gap stays much the same, so the distance shrinks. That’s why spacing that looks generous further out can compress at the runway.
Quick answers
How do you calculate closure rate?
Head-on, add the two groundspeeds. On the same track, take the difference. On crossing tracks it depends on the angle and on where the aircraft are, which is what this calculator works out.
How long until two aircraft reach the minimum?
Take the distance minus the minimum, divide by the closing speed, and multiply by 60 for minutes. Two aircraft 40 NM apart closing at 800 kt reach 3 NM in 37 ÷ 800 × 60, about 2.8 minutes.
What is the closest point of approach?
The moment two aircraft on steady tracks are nearest to each other, and how far apart they are then. If that distance is under the minimum, they’re in conflict unless one of them changes.
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For training and simulation only. These calculators are for learning and for games. Their results are automatic, and they don’t account for everything a real operation does. Never use them for real flight planning, navigation or air traffic control. Use your official charts, approved tools and procedures.
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