# Why would a commercal flight circle while enroute?

While selecting random flights to learn about FlightRadar24, I came across AC7311 flying from Toronto, ON (CYYZ) to Indianapolis, IN (KIND), and saw that it flew a couple of circles southwest of Lima, OH (near KAOH).

What are some of the reasons Air Traffic Control would direct the pilots to do that?

• that point is about 100 miles out from the airport, (at least on google maps' measure distance it is, – ratchet freak Feb 6 '15 at 19:38

As others have noted, this is called a holding pattern, which is used to delay an aircraft while in the air. Of course, this takes time and fuel, so the system works to prevent this from being necessary.

The primary use of holding patterns is by ATC to delay arrivals. This could for traffic reasons, to delay the aircraft until it can join the line of arriving aircraft. It could also be for facility reasons. Bad weather can reduce the rate at which an airport can accept aircraft, meaning some will have to enter a hold. An airport can also be closed for weather, or for another reason, in which case all aircraft must enter a hold, or land at an alternate airport.

Pilots sometimes need to use holding patterns as well. If they have an issue with the plane, they may need time to follow their checklists and diagnose the problem. ATC will give them a place to hold for this time.

Standard arrival procedures generally have holding points published for these cases. When a holding pattern isn't defined, one can be created. The aircraft will fly for a standard time before turning around, and repeating as necessary.

A better FlightRadar example is perhaps the following image, showing three aircraft in the stack and one leaving it

Source

• If I may ask -- which of the Heathrow stacks is depicted here? – UnrecognizedFallingObject Feb 6 '15 at 23:09
• @UnrecognizedFallingObject Based on the image here it appears to be Ockham. – fooot Feb 6 '15 at 23:22

It's called Holding Pattern.

ATC can direct a plane to enter the pattern in order to ensure separation between landings: two planes might reach the airport almost at the same time, the first might be directed to land, the second will have to wait.

• They would have them hold that far from their destination? I always envisioned holding patterns to be much closer to the destination airport. – FreeMan Feb 6 '15 at 19:37
• far is relative. Remember that you have to proceed to the approach and for large aircraft/airport it usually is several nautical miles long. – Federico Feb 6 '15 at 19:39
• @FreeMan Yes. Airliners fly quite fast (around Mach 0.85,) so their turn radius is not small and their descent/approach pattern is also quite long. Furthermore, they want to keep holding aircraft somewhat distant from the airport just for separation purposes with arriving and departing aircraft. Also, several different holding patterns may all be in use at once, so they need sufficient separation from each other as well. For example, when a thunderstorm passes over Atlanta International, a lot of arriving flights can back up very quickly and they all have to go somewhere. – reirab Feb 6 '15 at 22:42
• They don't typically fly at Mach 0.8 in a holding pattern, though :p – Jon Story Feb 7 '15 at 0:57

This maneuver of doing a 360° turn is issued by ATC. There are two reasons for this:

• to increase spacing between your flight and another airplane
• it was one or more circles in a holding pattern

By looking at the map, it appears that what your interested flight did was a holding pattern, because it is not too far to the airport.

• It's a holding pattern. Note that it's actually not a 360 degree turn. It's 2 180 degree turns with straight sections in between them, as is normal for a holding pattern. 360s are just that - 360 degree turns with no straight section and you just roll back out at the same point that you entered. – reirab Feb 6 '15 at 22:46