Speed and Spacing

Hey everyone!

Everyone loves flying with Air Traffic Control, especially Approach/Radar Services. This post is meant to give you an idea of how to help us out, make our jobs a little less stressful, and guarantee you better service.

Speed, and managing your energy, is important in any aircraft. We all know that landing too fast or too slow can have a big effect on just how much butter is left on the runway. But what about up in the air?

Setting the Stage
The majority of this post covers interactions with Radar Facilities. If you’re unfamiliar with anything, it might be good to read up here:

You’re talking to approach… now what?
Approach Tips | The Zipper Method

The first topic covers some terminology relating to approach and radar operations. The second is a good look at vectoring aircraft into a pattern from a controller’s perspective.

Effects of Speed on Turning Radius
An aircraft traveling in straight and level flight has a certain amount of inertia. Inertia is the principle of Newton’s First Law of Motion: An object in motion will stay in motion unless acted upon by an outside force. An aircraft in motion requires a certain amount of force to the side in order for it to overcome that inertia and turn. When an aircraft banks, the force of lift is divided into two components – vertical and horizontal. The vertical component of lift is what keeps the aircraft flying, it opposes gravity. The horizontal component is what fights inertia, causing the aircraft to turn; it is directed toward the center of rotation, and called the centripetal force (not to be confused with centrifugal force, which is what pushes you down into your seat).

You might think that’s a lot of words, and I agree. Let’s look at some pictures:
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The Glider Flying Handbook, Page 3-13

Two big things affect the turning radius of an aircraft: Speed and angle of bank. Since most of us use autopilot to comply with approach vectors, we will assume that everyone is banking the same amount, and that it isn’t a factor. Speed is a different story.

Speed is an important part of vectoring, especially when setting up a pattern and planning turns. Read more about how controllers set up patterns in the second article in Setting the Stage. Having every aircraft turn at the same airspeed/groundspeed helps ATC create patterns that are organized and reproducible, and will help get you on the ground quicker. Changes in airspeed have a large effect on the radius of a turn; the radius of a turn varies directly with the square of the airspeed. Meaning that an increase of 2x in airspeed will cause an increase of 4x in turning radius. This is because an aircraft traveling at a high rate of speed has more in If you’re buzzing around at 240 knots indicated, your turning radius will be almost 1.8 times bigger than what it would be if you were traveling at 180 knots indicated!

Flying slower, especially on a base leg, will help the approach controller give you an accurate vector to final. Has a controller ever cleared you, only for you to find yourself swinging way past the runway? This might be the reason why. It is easier for us to vector aircraft traveling slower accurately than it is to vector aircraft going full speed. I would recommend you not exceed 180 knots indicated airspeed on base unless otherwise directed.

Spacing: What Are The Requirements?
Radar controllers have some strict rules for keeping the sky organized. At all times, we are required to maintain 3 nautical miles of horizontal separation or 1,000 feet of vertical separation between you and any other aircraft. This means there should never be an aircraft within 3nm of you – ahead, behind, left, right, any direction. Any aircraft that is that close laterally must be at least 1,000 feet higher or lower than you. In practice, it is good to have more. As a pilot you should try to maintain roughly 5nm spacing with other aircraft, especially if you are behind them in an approach line.

Here’s a nice picture representing the separation requirements in Infinite Flight:
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IFATC Radar Manual

Josh’s article about the Zipper Method shows how controllers often try to get aircraft to follow a set path into an airport. It keeps us organized and makes things efficient for you. Controllers will also often have aircraft on the same leg at the same altitude. I tend to use 5,000’ AAL for downwind, 4,000’ AAL for base, and 3,000’ for intercept/final. If you find yourself in this position, it is imperative that you look around and listen. Know the callsign of the aircraft in front and behind you, and know where they are. If the aircraft in front of you is showing a ground speed of 160 knots, that’s annoying, but maintaining 240 knots won’t help the situation. Pull back on the throttle, and slow down to accommodate them. If you’re traveling along at 180 knots, and the aircraft behind you is instructed to maintain 220 knots or greater, you should speed up.

If you don’t do this, approach has ways of dealing with it, sure. Maybe you’re going to be directed to fly one leg of the pattern 1,000 feet high or low, to maintain separation. For us, we’re going to have to turn you and the other plane at different times, likely making our pattern bigger and messier. If this happens near final approach, you run the significant risk of being directed to execute a missed approach. Would you rather fly 40 knots slower, or go around the pattern again?

What Can I Do?
Remember that for all the aviation knowledge on this forum, no one was born knowing any of this. Be patient with yourself and others. When flying, especially when under approach control, look at the traffic around you, and pick a speed that’s in line with your neighbors. If one of them is told to speed up or slow down, maintain your spacing with them. If you’re getting close to being directed to turn to final, slow down to roughly 180 knots airspeed (if you haven’t already). Remember that as you go faster, your turning radius gets bigger, and it becomes harder for ATC to give you good vectors. Above all, follow all ATC instructions given to you.

Happy landings!

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Nicely done. Speed is the #1 reason why I see pilots not being able to make their approach intercept turn to final thus resulting in a missed approach. Trying to make that 30 degree turn going 245kts is going to send you wide.

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Just because you can go fast doesn’t mean you should go fast! Appreciate it.

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The other whippage is covered, nice. :)

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More information about whippage than anyone ever wanted!

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Absolutely great information. Thank you for taking the time to explain all that. Truly Awesome!!

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Yeah! Great explanation! Thanks @tomthetank! This is what I like about the IFC! We all keep learning thanks to posts like this. Great work!

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Really nicely put together! Very informative!

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