WAAS In It For You?

by Brandon Ray · January 28, 2014

Innovation Procrastination?

In the age of rapidly changing technology it is nearly impossible to keep up with the latest computer, tablet, or smart phone. Aviation is beginning to see similar technological innovation at a pace unmatched in any previous period of history. It’s amazing that until the past decade or so, our IFR system depended heavily on outdated and archaic systems of navigation

Did you know that some of the navigation technology in our modern planes has been around for over 80 years? NDBs (non-directional beacons) were first used in the 1930’s. While very simplistic, NDBs were an early step in building a foundation for IFR navigation. However, there were also limitations that spurred the need for more advanced navigation equipment, such as VORs in the 1950s and 1960s (very-high frequency omni range), which allowed for selection of specific radials, and a more complex and accurate IFR system.

Later came LORAN (Long Range Navigation) and RNAV (area navigation) which promised great capability of point to point navigation which meant no longer wasting time flying indirect routing to stay on the designated airways.

GPS (global-positioning system) was next and simplified point-to-point navigation and improved accuracy while relying only on satellites for the position calculation.

Now let’s talk about the latest and greatest innovation, WAAS – Wide Area Augmentation System. WAAS is basically GPS on steroids. It takes the existing infrastructure of the GPS satellite constellation and also uses a limited number of ground-based stations called wide area reference stations to improve the sensitivity of the position calculation. WAAS improves accuracy in both the lateral and vertical directions, allowing us to now fly GPS approaches which feature angular course guidance (similar to a localizer), and a glidepath (similar to a glideslope). Approaches with LPV minimums often have decision heights as low as 200 or 250 ft. AGL.

Before you start to criticize this young whippersnapper who is eager to adopt new technology, I’ve already heard all the horror stories and conspiracy theories about “the day the government decides to shut down GPS”. Yes, the US Department of Defense does control the GPS satellite constellation, and for a period of time they downgraded the GPS sensitivity to limit accuracy to an acceptable level for security concerns. This intentional degradation was called “selective availability” and was discontinued in May of 2000. Future satellites known as GPS III will not support this ability, so rest assured that GPS is here to stay.

What are the Benefits of WAAS?

  • RNAV/GPS Approaches with Vertical Guidance, many of which are just as good or close to ILS minimums
  • Lower minimums than traditional GPS approaches (LPV, LNAV/VNAV, or LP minimums)
  • More approaches at smaller airports
  • Encourages flying a “stabilized approach” rather than “dive and drive”
  • Improved safety during the approach phase of flight even in VFR conditions

How Does WAAS Work?

(Image source: www.faa.gov)

  1. GPS information is gathered by wide area reference stations (WRS). These stations are placed in precise locations where any necessary signal adjustments can be calculated. WAAS
  2. This information is relayed to the WAAS Master Station (WMS). WAAS step 2
  3. The augmentation messages are then sent from the WMS to the ground uplink stations to be transmitted to the geostationary satellites. The geostationary satellites stay above the US to support our country’s WAAS system. WAAS
  4. The corrected signals from the geostationary satellites get passed down to the end users to improve the accuracy and sensitivity of the GPS-calculated position. These geostationary satellite signals can also be used by the WAAS receiver as an additional source for calculation of the user’s position. WAAS

On an interesting side note: Other countries have their own WAAS-like systems, like EGNOS (European Geostationary Navigation Overlay Service) and MSAS (Multi-functional Satellite Augmentation System) that serve the same purpose. These are all considered types of satellite-based augmentation systems (SBAS).

What if I Lose WAAS?

The key term for GPS users prior to WAAS was RAIM – Receiver Autonomous Integrity Monitoring. We could check RAIM availability at any location to check for adequate signal coverage at a desired location. WAAS, on the other hand, features built-in integrity monitoring capabilities. WAAS systems have been designed to strict safety standards and will warn users within six seconds of any faulty information that could cause errors in the GPS position estimate. (This would be extremely rare in most parts of the US).

Summary

WAAS adds greater capability to general aviation aircraft offering safety and precise vertical guidance. LPV approaches now outnumber ILS approaches within the US. It is cost-effective, accurate, and provides the basis for the future of aviation navigation. Over the past decade, WAAS has grown significantly in popularity and is now standard in most new aircraft. Many GPS receivers can be upgraded or replaced to provide WAAS in any model of aircraft. If you have not yet upgraded, you may want to consider the benefits of adding WAAS to your airplane.

How it Started

One of my best friends in high school, (Doug Gray) was a private pilot. He offered to take me up for a flight in a 1967 Cessna 150, N6228S. We took off from Calhoun, Georgia, and he took me on a scenic tour of the area, I was hooked. I later found out that my English teacher, (Jan Haluska) was also a flight instructor and the school was offering a ground school course the next year, which he taught, along with flight training with the goal of becoming a private pilot. I managed to talk my dad into funding the training, at the time the total cost was right around $500. Cessna 150 rental rates where $12 an hour, and the 172 we used for cross country was $15 an hour including fuel.

Training Begins

It started August of 1977. The fall semester rolls around, and I am enrolled in ground school, and if memory serves me, we met twice a week. First came the paperwork for my student pilot certificate, which at the time was included with the 3rd class medical. I loved ground school, especially learning navigation, plotting courses on the sectional, again this was before iPads and GPS, so we did a lot of dead reckoning and VOR navigation for cross countries. At the end of the course, I made an 83% on the Private Pilot written exam, remember this was before we had the question-and-answer books that on future test I would consume before taking a written.

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Flying

The fun really began on August 22, 1977, it was my first flight. To my surprise we used the same Cessna 150, N6228S that my friend Doug Gray had taken me for a ride in. The Cessna 150 had a standard VFR instrument panel, with one NAV/COM, and one VOR CDI. No intercom, so no headset, at the time I didn’t know what I was missing. I didn’t get my first headset until I started my instrument training in 2003. I was a big guy, I was 6’ 4” and weighed 245 lbs. but I do not remember being uncomfortable in the 150 even with the instructor in the right seat.

First flight lasted .8 hours, and we accomplished orentation, shallow turns, stability, and effects of flight controls. Over the next few months we added steep 720’s, slow flight, stalls, turns around a point, S-turns, emergencies, landings, (short field, soft field and normal).

Learning

At this point I want to talk about a training experience that still stands out. We were close to solo and were practicing takeoffs and landings. Turning base to final Jan got very upset at the way I was cross controlling the aircraft. Cross control is when you are in, say a left turn, and use opposite rudder to line the nose up with the runway. So, he had me depart the pattern and head east to the practice area, and climbing up to 5500 feet MSL, he had me slow down to just above stalling speed, start a left shallow turn and add right rudder. As the airplane stalled I had the strangest sensation, no roller coaster has ever come close, instead of blue sky in the windscreen I was looking at brown ground, and as far as I could tell we were upside down, through the terror of the moment Jan talked me out of the spin, controls neutral, oposite rudder, pull slowly out of the dive. As we leveled off he asked me what altitude we were at, as I remember it was around 2,800 feet MSL. Then he asked me what would happen if I experenced this on base to final in the traffic pattern. The answer was obvious, I would be a pile of wreckage off the end of the runway with a very short-lived aviation career. Needless to say this cured my cross-control tendencies.

Another training event the sticks out in my mind was the first time we did takeoffs and landings at the High School runway. The runway was 1,500 feet long, not sure of the width, but it seems like we had about 5 feet on each side of the wheels when on the center line of the runway. Landing from the south you also had to go between a cutout in the trees to be able to stop in time on the runway. After getting confortable landing here every runway since seemed huge. I remember landing at Chattanooga (KCHA) on a night cross country and commenting to Jan, that I felt like I could of landed sideways on the runway, it felt that large.

Very soon after this I started wearing old shirts to all my flight lessons, the reason for this occurred on February 8, 1978. The lesson that day was stalls, takeoffs and Landing. As we were taxing back in Jan told me it was time for my first solo. I was very excited, and after some last minute advice from Jan, including watch for floating on landing the plane will be light with him not in the right seat, complete 3 takeoffs and landings to a full stop. It was a blast, and at the end of my shirt was shorter in the back because Jan cut the tail out of it signed and dated my solo [an aviation tradition]. Total flight time accumulated on the day of my solo was 18.1 hours. I was now officially a pilot with solo priveleges.

In my next article I start cross country training, when Jan decided that it would be best accomplished this in the 172. Checking out in N5970R was like moving into a 747, this started a love affair with one of my faviriote planes to date. Since this time I have flown over 900 hours in many different models of the 172 and feel like I am stepping into an old friend every time.

More about Randy here: https://www.flyhpa.com/team/randy-delong/

 

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