The Zipper Method
Greetings, ladies and gentlemen. Today’s post is intended to inform you all of a method approach controllers use when conducting approaches for aircraft into an airport. Broken into three distinct techniques, the “zipper method” is a great way to increase airport capacity and amount of aircraft handled. Below are some infographics and captionings to explain the concepts presented. Cheers!
- Disclaimer: altitudes, speeds, and downwind widths are theoretical concepts and not representative of actual commands an controller might give, not to be taken with a grain of salt.
Basic Zipper Example
- This is what you will often see when we split up our approach paths. Instead of all planes following one downwind, multiple aircraft are divided into two downwinds. Depending on the airport, there are a number of different techniques an approach controller can use to achieve maximum arrival efficiency for aircraft.
Technique #1- The Manual Zip
- At its most basic form, the zipper method consists of turning one plane’s base at a time, as demonstrated in the picture above. One runway airports such as San Diego benefit greatly from this.
- Although effective in modest traffic, following this technique based on vectoring alone has one drawback- lengthening the final approach line. You can tell from the arrows that each subsequent plane has to go further and further out.
- If all planes approach the final base turn at the same time and same speed, the controller would be required to send the second, third, fourth plane, etc, further out to build some spacing.
- The problems of this method can be solved with two simple solutions, depending on the type of runways available at the destination airport.
Technique #2- Speedy Zip
- As you can see here, the planes on right downwind to the runway have been assigned 180 knots IAS. The planes on left downwind are at 220.
- This type of method used in the zip allows the planes on left downwind to reach the base turn first, turning onto final before the planes on right downwind approach their turning point.
- Of course, slowing to final approach speed withstanding.
- This solves the issue of having to lengthen the approach line significantly, allowing for a true “zip,” turning one plane in after another consistently and seamlessly.
Technique #3- Parallel/Alternating Zips
- In this specific example, we have planes on both downwinds turning to Atlanta airport. Due to the multitude of parallel runways at the airport, it’s simply a matter of having both planes turn base when appropriate without worrying about them stacking on the same runway.
- One problem, however. With the “zip” concept putting both planes on the final turn so close to each other, separation has to be made.
- Therefore… the solution is to send one of the two aircraft at a lower altitude.
- 1,000 feet MINIMUM!
- The reasoning for this is to prevent both planes from colliding with each other if they fail to intercept and line up with the localizer at an appropriate time. Which, to be quite frank, happens to 70% of planes most of the time. Hence, it being a must.
- Essentially, you’ve killed two birds with one stone, making a double zip. You’ve increased your capability by twice as much and can funnel aircraft in on a rapid-fire basis.
What do you take away?
Hopefully, you may better understand why a controller is utilizing one of the techniques listed above while flying your aircraft. And, perhaps, if you control on occasion, you may find the information useful in creating a zipper method of your own.
Although there are even more techniques developed by our outstanding controllers, those are some of the most common, tried-and-true ones you will find. Try to work off a solid foundation of what you are given, and then add your own modifications on top of that. Everyone is different with how they control!
- Further disclaimer: Yes, I know. The name. But there’s really no better way than to call it the zipper method.