Order 7110.65R Air Traffic Control February 16, 2006 describes Timed Approaches from the Controller's perspective. The key here is that aircraft leave the approach fix inbound at a specified time. (A time check is issued to the aircraft before being given a specified time to leave the approach fix.) While Timed Approaches are less common "these days," they are still legal, and they can be (contrary to above posts) used in a radar environment.


As far as describing the approach goes, I think you may be looking for something far more complicated than it really is. For a timed approach, the pilot must adjust his timing to arrive over the Approach Fix (usually the Final Approach Fix) at the time assigned by ATC. How? By adjusting the holding patterns. The prescribed leg lengths for holding are maximum times. There is no minimum. If you chose to fly 360's over the holding fix, that would be legal. (It might be tough with a crosswind, but it would be legal.) So, consider a hypothetical clearance and a hypothetical holding pattern. Let's make this one no-wind for simplicity, and use a 1-minute maximum leg length. Including a standard rate turn on both ends, an inbound and an outbound leg, the maximum time for a single holding pattern is 4 minutes. Chop the leg length to zero, and the minimum time for a single holding pattern is 2 minutes (a 360 degree turn). Now, consider that you've just received a time check and a time to commence the approach. The difference between those times is, say, 15 minutes. Let's also say that you're currently inbound in the holding pattern, having just rolled out of your turn, and you have 1 minute until you arrive back at the holding fix/Final Approach Fix.

When you get to the Holding Fix/FAF, you will have used up one of those fifteen minutes, so you'll have fourteen more minutes to kill. How will you do it? One full turn in holding will take 4 minutes, leaving 10. Another will take 4 more minutes, leaving 6. Another full turn will take another 4 minutes, leaves 2. And you can do a 360 in 2 minutes, so you'd be golden, right?

Well, in a perfect world, that's true. Seldom do I find myself in a perfect world, and seldom do I fly perfectly, so I try to anticipate problems and avail myself of strategies to deal with them. Given the choice, I'd like to make the last holding pattern a complete pattern, or close to it, so I can have a little straight and level time approaching the Final Approach Fix -- after all, it's gonna be a busy action point, and I need to get myself prepared.

I might try something in between full patterns (4 minutes) and 360s (2 minutes) to put myself on a full pattern to end. With 14 minutes to kill, I might try one 4-minute pattern and two 3-minute patterns (30 seconds outbound, 30 seconds inbound), so that I can end with a 4-minute pattern. If it looks like I'm a little behind, I can turn inbound early on that last pattern to adjust. Or, if I plan on making the last pattern a 3-minute pattern, I can adjust both ways -- longer or shorter -- to make the time over FAF good.

Of course, when you throw in winds, you make the math a bit more complicated. Driving outbound for 40 seconds might result in a 60 second inbound leg -- how do you adjust the outbound leg to shave 20 seconds off the next pattern?


Right away you can see there's a good chance the pilot will screw this up -- and then you can put yourself in the controller's shoes and understand why they probably don't use them much if they don't have to. It's easier for them to vector us than give us a time that we will probably screw up. We screw it up, it screws up their plan, what should have been less work for them now becomes more work... well, you get the picture.


I think it was a good Instrument Ground question.






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