Wednesday, October 29, 2014

TAA's and ILSes (and other acronyms!)

Be ready for a few acronyms!

The FAA has recently begun adding GPS routes into ILS procedures, which in my opinion is a great thing! This combination of GPS and ground-based navigation allows for more flexibility for routing and easier flyability among other benefits. Here's what I'm talking about, see this example at Statesville, NC (KSVH).

If you're not familiar with TAA's (Terminal Arrival Areas), they are on many RNAV (GPS) approaches already but are just now being added to ground-based approaches as well:

TAA's allow you to be cleared for the approach anywhere within the depicted area, usually within 30nm of the fix shown (in this case PEGTE). The minimum altitude you must be at depends on distance and what your course is to that fix. So, in this example, coming from the west the minimum altitude is 4300 until within 6 nm of PEGTE, then 3400. From the east it's simpler, just 3400 all the way to PEGTE. Also notice that any course to the fix from 195 clockwise to 015 is considered a "NoPT" segment, so you can skip the depicted Hold-in-lieu-of-Procedure-Turn (HILPT). From the western half of the TAA you are still required to execute the HILPT in the example.

Another benefit of the TAA is that they do not require a VOR-based route into the procedure. Notice that the IF, PEGTE, is not anywhere on the Low Enroute chart (though there are some crossing radials, it's not on an airway). The TAA gives you the flexibility to be on a published segment of the approach, flying direct to PEGTE from anywhere within 30nm.

Another example is that at Rock Hill, SC (KUZA).

This one has a complete "T" setup of IAFs and the TAA to match. Unlike at KSVH, this allow you to come from essentially any direction and avoid flying the HILPT. If you're coming from the northwest, you'd fly direct to GUCRE, then be on a NoPT segment after reaching GUCRE headed to CONEL. The same idea with TAGCU from the northeast. From the south, you'd fly to CONEL and then proceed straight-in after reaching it.

One caution - if like in many airplanes, you're displaying both your GPS and ILS guidance on the same CDI, make sure to switch the CDI source as you reach the IF.

Another great benefit of a TAA is that ATC can clear you for the approach from a long way away. In order for ATC to clear you for the approach, you are required to either be on radar vectors OR established on a published segment of that approach. Since being within the TAA is considered to be on a published segment of the approach, you might be 28nm from GUCRE and hear a very simple "N123, Cleared ILS Y runway 2 approach"!

Now, many of these TAA-to-ILS approaches probably also have an RNAV (GPS) approach to the same runway with LPV minimums. In that case, if you have a WAAS-equipped GPS receiver, you'd probably just fly the GPS approach. But sometimes the minimums aren't quite the same, or there isn't an LPV approach to that runway for various reasons, so the TAA-to-ILS might be a benefit even with a WAAS receiver. If you AREN'T WAAS equipped, then the TAA-to-ILS is great, because it doesn't take a WAAS receiver to fly it!

For more about TAA's themselves, please see BruceAir's great blog post about them here. Highly recommended reading!

I expect to see more and more of these published as time goes on. Let me know if you see a new one!

(Acronym count: 12. I guess that's not too bad.)

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