WAAS up?

Nothing is more gratifying for IFR pilots than flying an approach down to minimums, breaking out of the clouds at the last second and greasing the landing. This is especially rewarding when the approach you’re flying has a 200’ DH with ½ mile visibility, and you take it right to the bottom. Traditionally minimums this low have only been available for ILS approaches at an airport that is lucky enough to be equipped with such.
But what happens when you’re at a smaller field, in bad weather and there isn’t an ILS available? You may be stuck with a non-precision approach that has minimums significantly higher than a precision approach, which may limit your ability to get into the airport.

This is where the beauty of WAAS-enabled RNAV approaches comes in.
WAAS is the Wide Area Augmentation System and we use it with RNAV (Area Navigation, mostly GPS approaches for GA aircraft). If you’re flying a newer aircraft, or an older airplane with upgraded avionics, you may already have WAAS—and if you do it’s an amazing tool in your IFR toolbox because you get a precision-like approach using only your WAAS-enabled GPS receiver.

WAAS uses error-correcting and signal integrity monitoring to provide a computer-generated glidepath (note–not a glideslope and not a BARO-VNAV glidepath) enabling a vertical track and lateral track on an instrument approach.

And WAAS delivers tangible benefits.

First, WAAS approaches within the continental United States have signal coverage that allows minimums down to 200’ and ½ mile visibility, the same as an ILS. This doesn’t guarantee that a particular WAAS approach at your local airport will have minimums that low, but they can be when the approach meets the appropriate terrain, obstacle and missed approach criteria.

Second, a WAAS approach flies just like an ILS. Outside of learning the particulars of your avionics suite, this approach will operate from a flying perspective just like every other precision approach that you’ve flown, which lowers the learning curve.

How do you know if an approach has WAAS? On a Jeppesen chart it’s easy.

Looking at the procedure name, you can see that the approach is an RNAV (GPS), since it has to be RNAV for WAAS to be even an option. On the second line, below the communication frequencies, you’ll see the first box identifies the approach as WAAS. Moving along the Briefing Strip sequence, you’ll notice in the minimums box it says LPV, which stands for Localizer Performance with Vertical Guidance. These are the WAAS minimums.

When you scroll down to the minimums section of the chart, note that the first set of minimums, if WAAS enabled, are LPV minimums.

If the approach doesn’t have WAAS, LPV won’t be listed. 
Here’s one other item of consideration. If you don’t have WAAS or lose signal integrity, the WAAS LPV minimums won’t apply and you’ll need to find the appropriate minimums on the chart.


About the Author: Craig Thighe is an Airline Transport Pilot, Gold Seal Flight Instructor, FAA Designated Pilot Examiner and recognized Technologically Advanced Aircraft expert. He has served in multiple capacities at Jeppesen and currently serves as a Business Partner in the Government Industry Affairs organization.

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