Story ID: 042
How WAAS Turned into a Must-have System
By: David Hughes
Caption: Once the subject of criticism, WAAS is on the majority of general aviation aircraft
Word Count: 2315
Twenty years ago, the FAA commissioned the Wide Area Augmentation System (WAAS), opening the door to satellite-based GPS navigation with accuracy, integrity, and consistent availability for an array of business and general aviation aircraft.
Leading up to then, WAAS had come under scrutiny—and criticism—after encountering several years of delays and mushrooming costs. Even so, groups such as the Aircraft Owners and Pilots Association strongly backed it.
And now, if you are a business aviator and not using WAAS, then you can count yourself in a minority. Most business aircraft rolling off the production line now are equipped to fly RNAV approaches with WAAS localizer performance with vertical guidance (LPV) minima.
Avionics repair shops also continue to upgrade aging jets, turboprops, and IFR-capable piston singles and twins with WAAS LPV, often as part of major full panel upgrades. It can cost $20,000 to $30,000 to upgrade a small aircraft with WAAS LPV and more like $200,000 to $300,000 for a business jet, according to several avionics repair shops.
What do general aviation aircraft owners get for the money? They get access to precision-like approaches with more than 4,100 WAAS LPV procedures that can, in many cases, match Category 1 ILS minimums down to 200 feet. LPV serves more than 2,000 airports, including more than 1,200 without ILS.
WAAS provides an accuracy of two to four meters for horizontal position by providing corrections to GPS from more than two dozen precisely surveyed ground stations throughout the U.S., as well as in Canada, Puerto Rico, and Mexico. These corrections are broadcast up to geostationary orbit satellites and then sent from there to avionics aboard aircraft.
The Safety Benefit
According to the FAA, WAAS provides pilots with more stable vertical guidance for approaches and enhances safety in all weather conditions. The Flight Safety Foundation points out that controlled flight into terrain accidents are significantly reduced by vertically guided approaches. ILS approaches can be affected by bends in the signals that can lead to a missed approach, the FAA noted.
There are only 1,290 ILS approaches in the U.S.—just about one for every three LPVs. Thus, many runways now havevertical guidance without having to maintain an ILS at the airport since WAAS approaches require no navigation infrastructure at the airport.
Some runways cannot have vertical guidance due to terrain or obstacles. WAAS localizer performance (LP) procedures provide for lateral accuracy similar to ILS for approaches where terrain or obstructions do not permit the vertically-guided LPV. The FAA says some manufacturers include an advisory glideslope so pilots can fly a stabilized descent to the minimum descent altitude even when the approach does not officially have vertical guidance.
There are 734 WAAS LP approaches to 734 runways at 537 airports—most of which do not have ILS. These RNAV approach procedures without vertical guidance have LP minima that can also be helpful when there is no precision-type approach available at an airport.
NBAA points to the benefits of the lower minimums provided by WAAS. “Our members value the precision-like minimums WAAS technology brings to the table. Many aircraft owners have equipped to take advantage of the capabilities and lower minimums at many airports across the country that aren’t currently served by an ILS,” said NBAA senior director of air traffic services and infrastructure Heidi Williams.
The Costs
When the FAA announced in July 2003 that it had commissioned WAAS, there were only 500 approaches with WAAS that had been certified at 200 airports. By 2003, the system had a cost of approximately $2.5 billion, including the then-estimated lifecycle costs through 2020 (which just so happened to be when the pandemic started). This was up from the initial 20-year lifecycle cost estimate in the early 1990s, before a $1.4 billion contract had been awarded.
To date, the costs incurred to develop and operate WAAS have reached nearly $3 billion, of which $2.7 billion is development costs, including satellite leases. The FAA said it costs $90 million to $110 million per year to operate and sustain the WAAS system.
At the time WAAS was commissioned, it provided an accuracy of 1 to 1.5 meters compared with 7 to 10 meters (vertically and horizontally) obtained from GPS without augmentation.
The U.S. Air Force is modernizing GPS and has already launched six out of 10 GPS Block III satellites that are expected to improve GPS accuracy by three times. These satellites broadcast on three frequencies—L1, L2 and the newer L5. However, the L5 signal won't become fully operational—expected later this decade—until it is broadcast from 24 satellites; currently, it is being broadcast from 17 satellites. 
In 2022, Raytheon Intelligence and Space was awarded an indefinite quantity contract with a ceiling of $375 million over the next decade for technical refresh and dual-frequency (L2 and L5) operation upgrades to WAAS. This will include more modern and sustainable processing, system security, and network architecture while adding dual frequency service in 2028.
The L5 frequency is designed to improve accuracy, integrity, and availability using dual-frequency-enabled WAAS receivers. Dual frequency (L2 and L5) will be especially helpful during ionospheric disturbances, including solar storms. The FAA adds that dual frequency will enable further expansion of WAAS LPV service in Alaska, Hawaii, Puerto Rico, Canada, and Mexico.
Legacy avionics may need a firmware or software upgrade to take advantage of the L5 WAAS frequency when it goes fully operational, according to Sam Pullen, a senior researcher at the Stanford GNSS laboratory. He holds a doctoral degree in aeronautics and astronautics from Stanford and an undergraduate degree from MIT.
Legacy WAAS equipment users will be able to get the same performance they are getting now by relying on the original L1 frequency.
Standalone GPS (without using WAAS corrections) is also adding the L5 frequency for aeronautical and other uses. The first six of the initial 10 GPS III satellites are now in orbit, and the other four will be launched by 2026 if things go according to plan. Standalone GPS III receivers will be able to counter ionospheric delay to reduce satellite error. The GPS ground control system is being upgraded, and this work has to be completed before dual-frequency (L1 and L5) operations can begin.
“The operational benefit will be higher availability, so you are more likely to be able to fly an approach to completion than before,” said Pullen. The boundaries on worst-case errors will be reduced, increasing both accuracy and availability. WAAS and other satellite-based augmentation systems (SBAS) may also provide corrections for the European Galileo system signals and potentially other Satnav systems. The European EGNOS version of SBAS already supports the use of GPS and will add Galileo support along with Galileo’s second frequency on E5a (the same as GPS L5).
Aviation isn’t the only community using WAAS, which is also found in agriculture, surveying, and maritime sectors. In aviation, regional airlines SkyWest and Horizon Air have installed WAAS on their aircraft, and Delta, Airbus, and Boeing are moving ahead with equipage.
At DeltaFox Aviation at Manassas Regional Airport in Virginia, a Part 145 repair station, co-founder Charles Schefer still frequently installs avionics to upgrade general aviation aircraft to fly WAAS LPV approaches. DeltaFox is a dealer or service center for Cirrus, Textron, Garmin, Avidyne, and Aspen Avionics, among others.
“I feel like 70 percent of the general aviation fleet is already upgraded to fly WAAS approaches, and most of the new business aircraft rolling off the production line [are] also already equipped,” Schefer said.
Mass Equipage
FAA data show that more than 75 percent of aircraft flying IFR in the U.S. have WAAS and LPV capability. The ADS-B mandate spurred WAAS equipage because WAAS-based ADS-B requires no performance prediction before entering ADS-B airspace.
“However, I see a lot of older jets that are not yet equipped and to upgrade one to fly LPV costs a lot,” Schefer said. “This often relates to the limitations of the autopilot, flight director, or other equipment currently installed.”
Older Collins Pro Line 21 avionics don’t support flying LPV approaches, and it may require a $20,000 supplemental type certificate (STC) to essentially trick it into thinking it is flying an ILS so it can display the approach parameters. Universal FMS and Garmin GTN avionics are WAAS-capable.
In some cases, the needles on a display are color-coded so pilots can tell if they are flying an ILS by seeing green needles, while magenta ones indicate flying a WAAS-guided approach.
Schefer did a lot of Cessna Citation upgrades to WAAS LPV, but most of the aircraft in that product line have been outfitted. When an STC box is not installed, the GPS is limited to use for lateral navigation, so it isn’t possible to fly an LPV approach with vertical guidance. Smaller general aviation aircraft flown mostly under VFR are seldom equipped because they won’t be flying WAAS LPV or LP approaches. “It wouldn’t make any sense,” Schefer said.
Schefer also operates a Part 135 charter business and recalls one trip he had to cancel with a Cessna Citation CJ2 to an airport without ILS. He said the former owner of the aircraft installed WAAS but not LPV capability, so he couldn’t use the LPV at the airport he was planning to fly to.
Bill Forbes, the director of avionics sales for Elliott Aviation, recounts a WAAS story that is posted online at the company's website. Elliott works on a wide range of business jets at three service centers in the Midwest, one in Texas, and one in Georgia. A few years ago, an Elliott customer was flying on a Hawker 800 on a business trip from Nashville to Lambert International Airport in St. Louis, the city’s main commercial airport. The ILS was out and the Hawker 800 pilot executed a missed approach but saw a Cirrus land right after that. A diversion led to the aircraft owner missing the important meeting in the city, and he ordered a WAAS LPV installation for the Hawker the next day.
In Lynchburg, Virginia, Jason Moorefield runs an avionics shop at Freedom Aviation that maintains Liberty University’s fleet of training aircraft and does avionics installations for other customers. The shop has three other technicians. Moorefield does WAAS LPV upgrades to aircraft several times per month, either as a standalone job or as part of a new panel. He notes that small business aviators like WAAS LPV for getting into airports that are located near the site of their day’s work but are not equipped with VOR or ILS.
He likes installing the GNC 355 all-in-one touchscreen GPS navigator with comm radios for light aircraft, which provides WAAS GPS navigation for LPV approaches. It pairs with selected Garmin flight displays or integrates with a course deviation indicator for a low-cost installation. Garmin lists the price of the GNC 355 as $7,695. Moorefield works on some jets each year and says a WAAS LPV retrofit for a jet starts at $200,000.
While the FAA is enabling satellite navigation, it is not giving up on maintaining ILS systems and some VORs for resilience. Jens Hennig, vice president for operations at the General Aviation Manufacturers Association, said some air navigation service providers in Europe are considering getting rid of some ground infrastructure. He thinks this approach is short-sighted.
Hennig notes that the FAA investment in WAAS has already been made. “The United States has a wonderful belt and suspenders system [with WAAS and ground-based navaids including ILS],” said Hennig.
“Now we do need to invest in teaching flight crews how to fly in that environment [without ground-based navaids] when there are maybe some challenges in the future,” he said, but added: “WAAS is a wonderful technology and the FAA continues to invest in it.”
FAA is working on an ILS Rationalization Program to decommission some ILS systems at smaller airports equipped for WAAS LPV approaches. It has not decommissioned any ILS systems yet or announced how many will be selected. But the agency has shut down 164 VORs and will shut down 139 more at a rate of 20 per year, ultimately leaving 590 running in its minimal operational network.
Analysis, coordination, and approval of the ILS program are required to identify candidate systems before any decommissioning begins. The FAA has contracts set up to replace aging ILS systems with state-of-the-art systems. ILS will be retained at airports where air carriers operate and along with VORs to ensure resiliency during GPS outages.
In Tulsa, Oklahoma, Joseph Hensley upgrades a lot of long-out-of-service turboprops that may have sat on a ramp somewhere for 10 or more years. He is the avionics manager for Intercontinental Jet Service Corp. Hensley said his shop installs WAAS LPV capability in these older aircraft along with completely new panels.
After purchasing the aircraft and installing new avionics, the new owners may have $1.5 to $3 million invested. But for an airplane like the Mitsubishi MU2 that can carry eight passengers with a single pilot at more than 300 knots, the cost per flight hour may be around $2,000 per hour with fuel consumption at 80 gallons per hour.
“It makes sense why these refurbished aircraft are so popular,” Hensley said. A similar new turboprop aircraft would cost $7 to $15 million. Most of his customers are doctors, lawyers, and salesmen who depend on these aircraft to grow their businesses.
Intercontinental is an authorized Mitsubishi and Piaggio service center. Hensley has upgraded 100 Mitsubishi aircraft and 40 Piaggios with new avionics systems, including most with WAAS LPV. A lot of these aircraft fly into small airports without ILS, so they need WAAS LPV capability to get there.