Understanding WAAS & LPV: What is WAAS?

What is WAAS?

Part 1 of 4: Find out how WAAS is a part of the FAA's Next-Gen initiative, the system network and coverage, and why installing WAAS-capable equipment doesn't mean you're ready to fly LPV approaches.

Questions? Ask us!

"What is WAAS" Video Transcript

Why Next-Gen?
GPS Augmentation
What is WAAS?
How Accurate is the System?
The WAAS Network
What is WAAS Coverage?
Is WAAS Worldwide?
Common Questions

Download the presentation slides.

My name is Gary Harpster and you're watching Understanding WAAS & LPV part 1 of 4: What is WAAS?

This presentation will be discussing what you need to know about WAAS for corporate aircraft and what's going on in our industry. I'll cover WAAS and LPV background and operations, and safety and efficiency benefits.

Why Next-Gen?

In 2025, the United States air traffic is predicted to more than double its current capacity. “Next Generation” is a word you hear floating around quite a bit, and it's a transformation of the existing National Airspace System (NAS). The goal is to increase capacity, decrease delays, and improve safety and security.

We move towards performance-based navigation (RNP). The terrestrial-based navigation that we're used to at this point in time will switch over to space-based navigation. All traffic surveillance and communications systems (CNS/ATM) will be satellite-based.

Current space-based navigation systems are incapable of supplying enough accuracy, integrity, continuity and availability for the most strenuous phases of flight with precision instrument approaches.

GPS Augmentation

GPS has to be augmented in order to give you the accuracy needed for this type of approaches. There are three methods to augment the GPS signal:

space-based (SBAS),
ground-based (GBAS),
and aircraft-based (ABAS).

Satellite-based system, or SBAS, is the WAAS satellite system. It is capable of providing accurate lateral and vertical navigation. It is a key enabler to provide RNP and SAAAR capable approaches worldwide. This is the direction that Next-Gen is taking us.

What is WAAS?

It stands for "Wide Area Augmentation System." WAAS is an extremely accurate navigation system which utilizes a combination of the global positioning satellites and geostationary satellites to improve the GPS navigational service.

Satellite-based navigation fits within the Next-Gen framework. It provides the same capability as a 60 year old Cat-1 ILS type of approach to more runways.

It's an FAA cost saver. So many decisions today are based upon cost and this is one that saves the FAA a lot of money. It eliminates the need for ground equipment infrastructure. It's a core element to transitioning to a satellite-based air traffic control system of the next generation.

How Accurate Is The System?

One to two meters (see presentation slides). That's about as accurate as you can get.

The WAAS Network

There's 31 constellations that make up the GPS network. There's 38 precisely located Wide Area Reference Stations across the country. These units provide correction to the GPS signal. They cover the continental U.S., Hawaii, Puerto Rico, Alaska, Canada and Mexico.

They collect and process the GPS information and send it to the WAAS master stations. There's two wide area master stations. They develop a WAAS correction message that's sent to user receivers via navigational transponders on the geo satellites.

There's two geosynchronized satellites. The WAAS messages, which improve the accuracy, availability and safety of the GPS position, give it one and half to two meters of horizontal and vertical accuracy.

There are four ground uplink stations and two operational control centers.

What is WAAS Coverage?

WAAS coverage covers the United States, Alaska, all the way down to Latin America and part of the Caribbean. On this slide (see presentation slides), it shows you where the vertical protection level is and the lateral protection level shows you have accurate signal all across the United States.

Is WAAS Worldwide?

No. WAAS is a regional augmentation.

There’s several space-based systems similar to the FAA’s plan that provide interoperability with WAAS avionics. Europe is working on a system (EGNOS). Japan is working on a system (MSAS). India is also working on a system (GAGAN). All of those units should be compatible with what we have in the United States.

Common Questions

A Question that is often asked is if I install WAAS-capable equipment, am I ready to fly LPV approaches? The answer is no.

WAAS receivers cannot be installed under a straight field approval. There’s a lot more to the field approval process. Once it’s installed in the aircraft, the installing agency needs to make sure that all equipment in the airplane is properly functioning. That means the autopilot, the scaling, everything that becomes a part of this equation needs to be checked. So it’s a lot more stringent than a straight field approval. Most WAAS receivers are installed under an STC.

WAAS-capable avionics do not automatically mean that you can fly to an LPV minimum. To accomplish the LPV minimums, you need dual WAAS receivers. They must be certified under TSO 145 or 146.

We’re often asked the question can I upgrade my existing navigational system to a WAAS receiver. And the answer is no.

Current systems are certified under TSO C129, a completely different criteria. TSO C145 and 146 means that the units are certified as a stand-alone receiver. No other signal needs to go into that box in order to give it the accuracy that it will present on your aircraft instruments.

It also requires an antenna change. The antenna’s are different from a TSO 129 box to what’s certified on a 145 or 146. Installation is currently being done by STC. It requires dual GPS receivers, other equipment mods such as the scaling and auto pilot, annunciation whether it’s external or on EFIS systems, and a flight test procedure are all required.

Contact Gary Harpster or a member of Duncan Aviation's Avionics Installation Sales team for more information.

Understanding WAAS/LPV Video Series

	WAAS Considerations: Introduction July 1, 2010 - Gary introduces the video series with a brief overview of key topics to consider if your aircraft isn't equipped with WAAS, including legacy interface problems, field approvals, annunciators, Next-Gen criteria, and how to determine if your aircraft is a candidate for an upgrade. » Watch "WAAS Considerations"
	Part 1: What is WAAS? July 8, 2010 - Find out how WAAS is a part of the FAA's Next-Gen initiative, the system network and coverage, and why installing WAAS-capable equipment doesn't mean you're ready to fly LPV approaches.. » Watch "What is WAAS?"
	Part 2: How WAAS Works July 15, 2010 - Learn how WAAS interacts with GPS signals, what augmentation messages do, and how they're processed. » Watch "How WAAS Works"
	Part 3: WAAS Benefits July 22, 2010 - Learn how WAAS changes navigational system accuracy, approaches, flexibility, precision, fuel savings and government and airport costs. Operational benefits and Next-Gen considerations are also discussed. » Watch "WAAS Benefits"
	Part 4: What is LPV? July 29, 2010 - Learn what LPV approaches are, how they benefit operators, and common equipment questions. » Watch "What is LPV?"