Skip to page content

Performance Success Stories

WAAS Procedures Offer Pilots New Access During Poor Visibility

Data Comm display showing departure clearance information.

Many WAAS-enabled instrument approaches are equivalent to a Category I ILS approach and provide pilots with stable vertical guidance to minimums as low as 200 feet.

  • WAAS allows pilots to take advantage of much more precise procedures without the need for VORs or instrument landing systems.
  • The technology helps pilots reach remote communities such as in Alaska where residents have no road service and are totally dependent on aviation for delivery of day-to-day necessities.
  • Procedures available with WAAS make flight cancelations less likely, an important advantage for Angel Flight, a service that provides free flights for adults and children in need of specialized medical care.
  • There are currently about 3,900 LPV and more than 660 LP procedures — at more than 1,700 airports across the country, compared to 1,500 instrument landing system (ILS) procedures nationwide.
  • Find out if GPS/WAAS approaches are available where you fly.

What began 15 years ago as a plan to increase airport access is now a major success in the FAA's modernization effort and continues to help to pilots across the country, especially those who regularly fly into remote locations and in poor weather conditions.

What is WAAS?

The Wide Area Augmentation System, or WAAS, is used by pilots in all phases of flight from departure to arrival. WAAS procedures — a form of Performance Based Navigation — are especially helpful during take offs and landings, giving pilots a whole new level of access to airports across the country that may have once been out of reach.

How does it work?

WAAS equipment works by providing extra information to an aircraft's GPS receivers to improve the accuracy and reliability of position estimates. So, what does this mean? GPS devices, like the ones we use in our cars, give us a close estimate of where we are located at any given time on the road, but they are not accurate enough for very precise movements such as aircraft procedures where an error of just a few feet could make the difference between a safe landing and a missed approach.

That's where WAAS comes in. The technology provides messages to the aircraft's flight management equipment, removing errors in the GPS signal and providing a much better estimate of the aircraft's location. This means pilots can take advantage of much more precise procedures without the need for VORs or instrument landing systems (ILS).


WAAS offers advantages over many traditional procedures.

  • There are currently about 3,900 Localizer Performance with Vertical guidance (LPV) and more than 660 Localizer Performance (LP) procedures — at more than 1,700 airports across the country — compared to 1,500 ILS procedures nationwide.
  • LPVs are WAAS-enabled instrument approaches equivalent to a Category I ILS approach, the most commonly used instrument landing approach. LPVs provide the pilot with stable vertical guidance to minimums as low as 200 feet.
  • As an added benefit, since WAAS uses GPS, procedures are available across the country. Traditional ground-based navigation aids only work within a particular geographic area. And, WAAS procedures are more reliable. ILS equipment, for instance, can go out of service. WAAS is available wherever GPS is available.

The Live-Saving Impact of WAAS in Alaska

Small plane landing on snow covered ground.

The impact of WAAS is no greater than in Alaska where access to airports can make the difference between life and death.

"Eighty-two percent of the communities have no road service and are totally dependent on aviation for not only emergency services, but even more so in the delivery of day-to-day necessities," said Dennis Parrish of the Alaska Governor's Aviation Advisory Board. Some of these areas are so remote, the only way food, medication, and other vital supplies make it into the small towns is by airplane.

Parrish said due to the demand for regular air service in Alaska, and the pressure to provide service because there are no roads, Alaska has traditionally had the highest annual aircraft accident record in the nation. He credits WAAS for helping to change that. "The stabilized approach to airports with limited infrastructure, which this service provides, has saved many lives in our state," he said.

"Conditions up there are so severe and so different," said JoAnn Ford, an FAA engineer and Alaska Liaison for the agency's navigation programs. "With these smaller villages, all they may have is a small runway. There's no fixed based operator there, no lighting system, and no automated weather systems, so the ability to fly into the airport even though there's no control tower is key. And, with WAAS they have a published approach, so they can gain access."

Ford says WAAS is helping not only during approaches and takeoffs but during the entire flight. In Alaska, pilots can't fly T-routes — designated routes from 1,200 to 18,000 feet — without WAAS. "WAAS enables minimum en route altitudes, sometimes as low as the minimum obstruction clearance altitudes," she said. "If you just have GPS, you don't have the ability to fly lower, out of icing conditions."

The WAAS Effect for Angel Flight

Steve Craven pilots a Piper Saratoga. As a volunteer for Angel Flight — a service that provides free airlifts for adults and children in need of specialized medical care — he says he relies on WAAS procedures to get in and out of airports in remote locations. It's not uncommon for Craven to fly to and from mountainous regions or in poor weather conditions as he helps patients make it to their appointments, often hundreds of miles away from their homes.

A man standing next to a planes nose propeller

Steve Craven, a volunteer pilot for Angel Flight, relies on WAAS procedures to fly patients to important medical appointments.

Craven, who is the former chairman of Angel Flight in the Mid-Atlantic region, says these flights are particularly helpful for patients living in rural areas without access to state-of-the-art treatment facilities. "If someone has an appointment, at Sloan Kettering Cancer Center, they want to know they can get there," he said. "Greater access makes all the difference in the world. In the past without WAAS, we'd frequently have to cancel the flight because of a low ceiling."

Craven has flown many patients to and from hospitals all along the Mid-Atlantic and Northeast states including face transplant patient Richard North who lives in a small town in a mountainous region of southwest Virginia. Following his surgery, North required twice monthly visits to his doctors in Baltimore.

Craven calls the airport he flew in and out of to transport North a "nasty little airport between the ridges." He says WAAS provided more consistent access to the airport. "Before WAAS, if I got a weather forecast and the ceiling was 500 or 600 feet, we could not get in. WAAS changed everything," he said. "It provides an approach with a glideslope we didn't have before."

WAAS for Air Carriers

A large cargo plane on a runway in the snow.

WAAS is already benefiting airlines and air cargo companies in Alaska and Canada. "WAAS navigation changed the landscape for Alaskan air carriers," said Jane Dale, director of the Alaska Air Carriers Association. "In southeast Alaska, lower altitude routes available with WAAS enable carriers to fly instrument flight rules point to point," she said.

Although carriers have multiple alternatives to land at an airport, often the weather conditions do not allow for certain procedures, or instrument landing systems are down or not available. She said, "For regional jets, WAAS becomes important to them. They are transporting people, mail, supplies, and delivering things that one wouldn't think air carriers would carry." Dale says WAAS provides both safety and access to those using WAAS procedures.

Canadian North Airlines uses WAAS regularly and it's good for business according to Chris Drossos, director of flight operations and a pilot at the company. The airline's entire fleet of 737s is equipped to perform WAAS procedures. The aircraft transport people, cargo or a combination of both in Canada, parts of the United States and Mexico. Drossos says there are times when the airline cannot land at certain airports in Canada, especially without WAAS technology because of low ceilings and visibility due to poor weather conditions. Adding to the complexities, he says the airline serves a number of airports without instrument landing systems in place.

Conventional procedures are sometimes an option but he says WAAS is often the better choice during very bad weather. "It gives you far more precise guidance than barometric VNAV so for conducting stabilized approaches, it's a great gauge in maintaining a proper glide path particularly in conditions where the visibility and gusty winds are a problem. It keeps you on the profile," he said. "Normally we'd have to temperature correct these altitudes using a chart. Of course, the LPV glide path is unaffected because it's a geometric glide path, and it's not affected by an altimeter source."

Drossos says the technology helps the airlines save money. "We don't have to divert somewhere else and then possibly wait for the weather or have to wait for ground transportation, so our reliability for maintaining the schedule is far better with WAAS LPV," he said. "For some of the private airports we fly into, there's no cost putting in all the ground based NAV aids that would be required for an instrument approach procedure."

WAAS Success

The FAA began activating WAAS procedures in 2003, launching about 500 per year. At first, WAAS procedures featured a decision altitude of 250 feet. In 2008, the FAA reduced the decision altitude to 200 feet, which provides even better access to airports.

Deployment of WAAS equipment is now complete, and the FAA is looking to convert current Localizer Performance (LP) approach procedures to LPVs were possible. LP procedures are WAAS approaches that do not include vertical guidance. There are more than 660 LPs at over 400 airports across the country, typically at locations where terrain or obstructions make it harder to publish LPVs.

Enhanced Coverage

Info graphic.

The FAA is also working to enhance WAAS coverage in the most remote parts of the country with a new satellite. "In order to enable WAAS technology, we not only utilize the entire constellation of GPS satellites in view, but we also have three geosynchronous satellites," said Ford.

This type of orbit allows a satellite to travel at the same rate as the Earth's spin, keeping it in relatively the same position above the earth at any given time. "That's what makes the difference as far as the accuracy, availably, and integrity of WAAS compared to just GPS alone," she said.

The FAA currently has three geosynchronous satellites (GEO) orbiting the earth. In March 2018, the 5th WAAS GEO (GEO 5) became operational which is particularly helpful in Alaska. Greg Thompson of the FAA's Navigation Programs–WAAS Program team, says WAAS currently provides coverage over the entire state but the northwest portion is covered by only one satellite.

"While this does not have an impact to WAAS operations, it does present a risk to that area if something should happen to the satellite," he said. "With the integration of GEO 5, the entire state of Alaska will have redundant coverage eliminating the risk of a service outage in northwest Alaska."

Page last modified:

This page was originally published at: