A bumpy landing?
- By Paula Shaki Trimble
- Apr 03, 2000
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.