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With WAAS, Everyone Should Know


October 15, 2007
By Rob Seaman

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wso4In the beginning there was GPS – and we were all amazed and felt comfortable venturing into the unknown. But there were a lot of “could be” problems – like when the military decided to tune things down during moments of crisis (after all, they do control the satellites that run this whole system). Or atmospheric influences and a range of other things.

Then we started to hear about DGPS – Differential GPS.  With DGPS, an airfield places a special transmitter on the ground that sends a signal to a “Differential Receiver.”  This receiver plugs into a GPS and the resulting signal removes all of the error caused by slight errors in satellite orbit, errors introduced by the atmosphere and the minuscule errors on the GPS atomic clocks. The objective is to improve the accuracy of the GPS receiver to enable an ILS approach with it, possibly down to CAT III.

So what could possibly be better, you ask? Well hang on, because here comes WAAS!

Garmin, unquestionably one the leaders in GPS technology, describes WAAS (Wide Area Augmentation System) as a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three metres 95 percent of the time. The exciting news is that the FAA, DOT and Nav Canada are developing WAAS for use in many aspects of current and planned navigation system upgrades and aids. Among these is the capability for precision flight approaches. As it stand today, GPS alone does not have the accuracy, integrity or availability to do this. But because WAAS corrects for GPS signal errors caused by ionospheric disturbances, timing, and satellite orbit errors, and it provides vital integrity information regarding the health of each GPS satellite, it allows for such improvements.

How does WAAS Work?
WAAS is a series of ground reference stations that monitor GPS satellite data. The collected data from the reference stations creates a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal. WAAS was first approved for use in Canada in October 2005. The lack of Canadian-based ground reference stations has made the service spotty; but this year WAAS systems have been established at Gander, Goose Bay, Winnipeg and Iqaluit. This means that by the end of 2007, most Canadian airspace will be WAAS-capable.

At the recent CBAA convention in Calgary, one of the leading presentations was a joint effort by Nav Canada, Transport Canada and International Business Aviation Council (IBAC) to discuss CNS/ATM (Communication Navigation Surveillance/Air Traffic Management) and the changes to air navigation systems not only in Canada – plus the role that this will play in corporate aviation. WAAS has an integral role in this. As IBAC’s director general, Donald Spruston, stated in his presentation, CNS/ ATM is a complicated but exciting game. There are several components to this – technology is an important one, performance is another – and SAT/Voice Data is a unique conversation unto itself.

Spruston’s biggest concern is whether the business aviation industry will be ready for the challenge. He illustrated how CNS/ATM will be implemented in all corners of the world at some point and how it will be phased in at different times in regions. Many of the elements are already implemented, particularly on the NAT (North Atlantic Tracks) and in Europe. IBAC’s role in changes of this magnitude is to make certain that corporate aviation’s interests are properly addressed as the CNS/ATM systems and changes come into play.

Ross Bowie is Nav Canada’s director of ANS Service Design. As part of the same presentation, he went on to state that over the coming years there will be fewer ground-based navigation aids in Canada as WAAS moves to become the new standard. In support of this he pointed out how traditional GNSS (Global Navigation Satellite System) signals are weak and prone to interference or compromise (something we are more aware of in the enlightened security consciousness of today). Bowie also pointed out that those who do not like WAAS do so more for political than technical reasons. An example is nations that are developing a competitive system – Russia, for instance. Other governments are developing similar satellite-based differential systems. In Asia, it’s the Japanese Multi-Functional Satellite Augmentation System (MSAS), while Europe has the Euro Geostationary Navigation Overlay Service (EGNOS).

So apart from improved accuracy, how does WAAS help? Improved and more accurate navigation is a benefit at many levels. More accurate navigation simply means you can get from point A to B better and faster. From a cost perspective there is better use of fuel burns. And as the result of all of this, lower emissions from aircraft into the now sensitive environment. That in turn means we as an industry are contributing less to the carbon emissions bank (a term and process we will all need to be familiar with in the coming years). So, by refining and improving the overall CNS/ ATM system – and in particular increasing the use of WAAS – everyone benefits.

Currently, WAAS satellite coverage is only available in North America. There are no ground reference stations in South America, so even though GPS users there can receive WAAS, the signal has not been corrected and thus would not improve the accuracy of their unit. For some users in the US, the position of the satellites over the equator makes it difficult to receive the signals when trees or mountains obstruct the view of the horizon. WAAS signal reception is ideal for open land and marine applications. WAAS provides extended coverage both inland and offshore compared to the land-based DGPS. Another benefit of WAAS is that it does not require additional receiving equipment, while DGPS does.
Eventually, GPS users around the world will have access to precise position data using these and other compatible systems.

Is WAAS demand up today?
Kitchener Aero/Mid-Canada Mod Center president Barry Aylward says WAAS GPS is arguably the hottest topic in the marketplace this year. He adds that both shops have been extremely busy with Garmin GNS-430/530 WAAS upgrading. And Universal Avionics has now confirmed its WAAS upgrade program for the UNS family of Flight Management Systems, so activity will likely ramp up quickly with that product line as well.

And just so you don’t think Garmin are the only folks in this business of GPS/WAAS, at the most recent edition of the EAA’s AirVenture in Oshkosh, Wis.,  Honeywell’s Bendix/King division unveiled two new products designed to win back market share from their rival. The Bendix/King KSN 770 is a GPS WAAS navigator with integrated VHF navcom radios, joystick cursor controller and 5.7-inch-diagonal VGA display. It goes head-to-head with the Garmin GNS 530W navigator. So the OEMs are ramping up, the nav system providers are sending and setting things in place and the public is getting on board with the systems and upgrades. Given that WAAS is a satellite based system – dare we finish by saying the OEM wars in this area could be – are you ready – Star Wars? Only time will tell.


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