The Duncan Download Blog: Business Aviation Advice & Observations

Gary Harpster, Duncan Aviation Avionics Sales Rep continues the Understanding WAAS & LPV video series.

WAAS is supported by a sophisticated infrastructure across the United States consisting of Wide Area Reference Stations (WRS), Master Stations (WMS) and a terrestrial satellite network. Learn how the WAAS signal interacts with GPS, eliminating inaccuracies and providing precision approach information.

View the complete WAAS/LPV video series at www.DuncanAviation.aero/videos.

Gary Harpster, Duncan Aviation Avionics Sales Rep explains all you need to know about WAAS & LPV for corporate aircraft and what's going on in our industry, covering operations, safety and efficiency benefits.

Business Aviation has another group of letters to add to its alphabet soup of acronyms. WAAS, Wide Area Augmentation System, is an extremely accurate navigation service which utilizes a combination of the Global Positioning System (GPS) satellites and Geostationary Satellites to improve the GPS navigational service. But what is it? How does it work? And will it be where I need it?

Questions about WAAS/LPV? Ask them on the What is WAAS? video page.

View the complete WAAS/LPV video series at www.DuncanAviation.aero/videos.

Gary Harpster, Duncan Aviation Avionics Sales Rep introduces the Understanding WAAS & LPV 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, NextGen criteria and how to determine if your aircraft is a candidate for an upgrade.

NextGen is the next generation of air traffic control and aviation communication/navigation. WAAS/LPV is the latest in aircraft avionics and will be necessary to meet NextGen criteria. But there are many things you must consider before heading down the road towards this upgrade.

Questions about WAAS/LPV? Ask them on the WAAS Considerations video page.

View the complete WAAS/LPV video series at www.DuncanAviation.aero/videos.

WAAS is a complicated subject. We've written a book, a whitepaper, magazine articles and press releases on the subject, and the questions are still rolling in.

Of the hundreds of WAAS inquires I've seen, this one stood out. Someone asked, "Why?"

The question was, "You mentioned that some installations may require two WAAS receivers to be certified to fly LPV approaches. Why? I don't see that as a requirement in any of the FAA advisory material. What is it about WAAS and LPV that requires two Flight Management Systems and two GPS receivers?"

The answer, of course, is complicated. The following explanation was provided by Avionics expert and AEA Vice Chairman, Gary Harpster: 

Prior to WAAS receivers, the Flight Management Systems were certified under TSO C129. TSO C129 allowed an operator to use a single FMS for a GPS approach as long as it was an overlay approach. This also required alternate navigational imputs, such as VOR, DME, ADF, etc.

The new WAAS receivers and Flight Management Systems are certified under TSO C145 and C146, allowing a very precise GPS approach without any additional inputs. These systems also have a unique feature: they are constantly doing an analysis of the GPS integrity. Part of this analysis is a cross check of the secondary system, which adds a high degree of reliability. 

One of the challenges of Air Traffic Control is to put multiple aircraft into a confined corridor and keep them properly separated. The new WAAS receivers are designed to accomplish this- the secondary system is a necessary backup in case of the failure of the primary system.  

Some manufacturers have designed WAAS monitors to act as a secondary FMS without a Cockpit Display Unit. This configuration provides the required redundancy without the expense of an entire second system. 

Do you have a question about WAAS? Ask it here.