A bumpy landing?

The Federal Aviation Administration may have created expectations about

satellite navigation that it cannot deliver, FAA officials say.

As an independent panel of experts works to iron out problems with the

integrity of the agency's Wide-Area Augmentation System (WAAS), the FAA

is leaving open the possibility of scrapping the more ambitious elements

of the program.

The FAA still expects WAAS to provide pilots with an unprecedented ability

to land during limited visibility — what is known as precision approaches — but it may be up to the aviation industry to define the limits.

"We want to build satellite navigation to the extent the user community

wants it," said Carl McCullough, director of the FAA's Office of Communications,

Navigation and Surveillance Systems. "I'll be the first one to admit satellite

navigation has been oversold."

The FAA is proceeding with plans to offer a navigation capability in

2002, known as Lateral Navigation/Vertical Navigation (LNAV/VNAV) that will

allow pilots to use WAAS when their aircraft are as close as 350 feet above

touchdown and there is as little as one mile of visibility.

WAAS is a network of ground reference stations and communications satellites

that correct and verify signals received from the Defense Department's 28-satellite

Global Positioning System and broadcast that information to pilots.

Prime contractor Raytheon Co. is expected to fix some software problems

that affect the stability of WAAS by September. However, new algorithms

are needed for software that indicates to pilots when the GPS signal is


An independent panel, called the WAAS Integrity Performance Panel, is

expected to deliver its recommendations for how to fix the integrity problems

in six to nine months. Experts from Stanford University, Ohio University,

Mitre Corp., NASA's Jet Propulsion Laboratory and Raytheon are part of the


One major question is whether the FAA should continue to pursue WAAS-based

Category 1 approaches, which can be as close as 200 feet above touchdown

and with navigation visibility as little as a half a mile. The FAA wants

to know whether the aviation industry believes it is worth waiting for that

capability and whether it is willing to bear the cost of equipping aircraft

and airports to take advantage of it, McCullough said.

Depending on the outcome of the study, the FAA may shift more resources

to another GPS augmentation system, the Local-Area Augmentation System (LAAS),

which consists of ground stations installed at 143 airports and avionics

systems installed on airplanes that will provide positioning information

for pilots to land aircraft in even lower visibility than WAAS would allow.

In six to nine months, the FAA will know more about how far to go with

WAAS and the ripple effect it will have on the phaseout of ground-based

navigational aids, said Steve Hodges, FAA satellite navigation product team

leader. The agency may determine that it is better to buy more LAAS equipment.

"Technically, it's still feasible for WAAS to meet its objectives," he said.

WAAS is essential for the success of other FAA modernization programs,

such as the Automatic Dependent Surveillance Broadcast and Free Flight,

which will allow pilots to choose flight routes rather than fly predetermined

paths. Such flexibility will enable pilots to choose the most fuel-efficient

paths and avoid weather problems.

The 350,000-member Aircraft Owners and Pilots Association still wants

to reach the Category 1 equivalent with WAAS, said Warren Morningstar, AOPA's

vice president for communications.

"LNAV/VNAV is a reasonable interim point, but we're not going to be

happy stopping there," Morningstar said.

Many runways are not equipped with the costly existing Category 1 approach

system, called the Instrument Landing System, he said. An Instrument Landing

System costs about $1.5 million per runway end. An alternative to ILS is

needed, he said. "WAAS, if it meets its promise, provides some real benefits

to the users," Morningstar said. "Then the users will voluntarily equip."

The agency has requested $113 million for WAAS in fiscal 2001.


Wide-Area Augmentation System:

A network of ground reference stationsand communication satellites that correct and verify signals from the DefenseDepartment's 28-satellite Global Positioning System and then broadcast thatinformation to pilots.

Local-Area Augmentation System:

Ground stations installed at 143 airportsand avionics systems installed on airplanes that will provide positioninginformation for pilots to land aircraft in even lower visibility than WAASwould allow.

BY Paula Shaki Trimble
Apr. 3, 2000

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