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Sunday, September 1, 2002

Is LAAS Cat I Close at Hand?

David Jensen

The contract for a Category I version of the Local Area Augmentation System may come soon. It would represent a giant step forward, but more giant steps will be required for the satnav system to reach its full potential.

The proposals were submitted this summer, and the long-awaited contract for a Category I Local Area Augmentation System (LAAS) is expected to be awarded soon, perhaps by the end of this month. It will represent a giant step in satellite navigation at a time when enthusiasm for space-based navigation has been tempered by the results of a GPS vulnerability study conducted by the U.S. Transportation Department’s Volpe National Transportation Systems Center and by the Federal Aviation Administration’s (FAA’s) decision to maintain its network of instrument landing systems (ILS).

At one time, LAAS was thought to be the ILS replacement, and that still may occur. But first the FAA program must vault some tall hurdles, which will take years to achieve. The agency is advancing the program cautiously, one step at a time.

Keeping ILS

"For the foreseeable future we will see a combination [of LAAS and ILS ground systems] to provide precision landing," says Steve Hodges, LAAS product team lead for FAA. "The makeup of the combination will depend on the deployment of LAAS and equipage by the [aircraft user] industry."

Hodges’ comments were reinforced at the Navigation Architecture Industry Day in early May, which was held to propose the future mix of navaids in the United States. Sponsored by the Mitre Center for Advanced Aviation System Development (CAASD), the event revealed FAA’s proposal to, among other things, retain at least one ILS at U.S. airports that have the landing aid and keep all Cat II and III ILS.

Competing for the winner-take-all LAAS contract are two teams. One joins Honeywell and Lockheed Martin ATM and the other includes Raytheon and Thales ATM. This teaming arrangement changes the LAAS landscape, which before had involved Honeywell, Raytheon and Thales developing a Cat I system separately under a government-industry partnership (GIP) in Phase I of the LAAS program.

The LAAS proposals responded to a screening information request (SIR), which is similar to a request for proposals (RFP) but is exempt from standard government acquisition requirements. As its name implies, a SIR works as follows, according to Bob Meyer, director of business development for ATM systems with Raytheon ATM: "You provide information and the FAA, which provides program oversight, can screen you out."

The contract calls for 10 initial production systems for LAAS full-scale engineering development and priced options for 15 to 40 production systems per year for five years, which probably will be installed at airports with high-density traffic. Each installation will include the following:

Four reference receivers with antennas, which must be located within 5 nautical miles (nm) of the central, main processing unit, which will receive, decode and monitor GPS satellite data;

A central, main processing unit that receives and compares the four signals (throwing out any errant signals) and produces a correction message by comparing known ranges based on the GPS signal;

Redundant VHF data broadcast units with a single antenna, which deliver the correction message to the airborne receiver via a data link with D8PSK standard modulation format; and

Equipment racks for the transmitters and processors.

From this ground system the airborne receiver will use the correction message data to compute the aircraft’s position, velocity and time (PVT) for area navigation or for a precision, instrument flight rule (IFR) approach. The ground system also uplinks reference points that define precision approach paths.

Four of the initial production LAAS systems will go to the FAA Technical Center near Atlantic City, N.J., and the Mike Monroney Aeronautical Center and Training Academy in Oklahoma City, while the remaining six units will be installed at commercial airports. The contract will usher in the LAAS program’s second phase, according to Hodges.

A Prudent Approach

"We will have a Joint Resources Council (JRC), which will make a decision in 2005 to see if we have progressed far enough to develop a Cat II and III system," the FAA product team lead adds. This represents a prudent approach on the part of the FAA. "Instead of saying 100 percent we’re going into development [of Cat II and III ground systems] in 2005, we’re saying we will have a JRC decision then," says Hodges, referring to the year the LAAS Cat I is to enter initial operational capability (IOC).

Such prudence is not totally in reaction to the Volpe Center study, released in September 2001, according to Hodges. "I want to emphasize that the Volpe study did not identify new concerns that we weren’t aware of [but] it did reinforce those concerns.

"We want to do true research and development before we award a full-scale development contract [for Cat II and III systems]," he adds of LAAS Phase 2. "We want to make sure we can make the required performance and be clear on expectations."

Assuming the FAA receives such assurance, the LAAS program will proceed to Phase 3, the full-scale development and production of ground systems with the "end-state configuration," according to the FAA, referring to in-operation Cat II and III systems. Phases 2 and 3 also will involve the development of advanced procedures, such as curved and segmented approaches, using LAAS.

Reaching the performance goals for Cat II and III will be challenging. Development costs for a Cat II system have been estimated by industry at $25 million and for a Cat III system, $50 million. Hodges would only say that, compared to the FAA’s internal estimates, those figures are "in the ballpark."

Yet Cat III performance is the goal the LAAS program must reach to gain support from the airlines, which enjoy ILS performance to Cat IIIb. Meantime, Hodges believes the Cat I LAAS system can serve the airlines and other airspace users in numerous ways.

The Benefits

It can, for example, provide an "option" to Cat I ILS, as well as offer more flexibility than ILS. "You can exercise advanced procedures with LAAS, such as segmented or curved approaches for, say, noise abatement and efficiency," says Hodges. (Initially, however, LAAS would be approved for landings within an "ILS look-alike zone" only; further spec development and additional training for both pilots and air traffic controllers would be needed for new types of approaches.)

LAAS also can provide precision approach capability on runways that have no ILS or have ILS only at one end, Hodges adds. While an ILS system is required at the end of each runway on which aircraft make approaches, a single LAAS system can provide precision approach capability at both ends of all runways on an airport. With Cat III performance, LAAS could be used for ground navigation, as well. "Also, the LAAS signal can provide guidance at a greater distance–23 nm from the airport as opposed to 10 miles with ILS," he adds.

Building a Business Case

To further verify LAAS viability to the user community, FAA is "about to conduct" a business case for the technology, according to Hodges. "Actually, we will be updating a benefits case completed in 1999, to make sure it is still applicable. The business case study will involve many airlines and some airports."

In addition, Mitre CAASD, which has been involved in LAAS development since its inception, is conducting a study to determine "what kinds of runways would best be served by LAAS," according to David Hamrick, Mitre CAASD’s associate director for CNS (communication, navigation and surveillance). "Using GAME [GPS approach minima estimator] modeling, we will look at where LAAS can be installed for runways that do not have ILS, to see if the system will improve minimums."

Mitre CAASD has just begun its research and will coordinate with FAA, which will provide a list of airports for the study. (GAME combines an airports data base, terrain data base, obstacle data base, approach design criteria and minima estimation software to make its calculations.)

Federal specification for LAAS Cat I certification have been completed and harmonized with the International Civil Aviation Organization’s (ICAO’s) standard and recommended practices (SARPS) for ground-based augmentation system (GBAS–the non-U.S. designation for LAAS) Cat I. Also, RTCA has finalized the minimum operational performance standards for LAAS Cat I, and has begun developing the specifications for LAAS Cat II and III.

Tough Nut to Crack

The easy requirement for LAAS to meet would be accuracy. "We’ve already demonstrated that down to Cat III requirements," says Mike Hoodspith, Honeywell’s marketing manager, satellite landing systems. The integrity, or safety assurance requirement is believed to be the most challenging to meet. It was the issue that delayed LAAS’s sister satellite positioning program, the Wide Area Augmentation System (WAAS). (WAAS developer Raytheon says it has overcome this hurdle by developing new, safety algorithms.)

The integrity requirement for LAAS Cat I is a 2 X 10-7 chance of providing undetected, hazardously misleading information, and for Cat III, it is "tentatively" 1 X 10-9, says Hodges, though FAA has not finalized that requirement yet.

"Integrity is the toughest nut to crack," admits Hoodspith, "but it is not a show stopper by any means. Cat I [integrity] will not be a problem and, as for Cat II and III, it depends on the final architecture design that the FAA requires."

"Through a huge amount of modeling and validation, we’ve found that Cat I integrity is very achievable," adds Tim Katanik, Raytheon’s manager of business development for navigation and landing systems.

LAAS integrity relies on the reference receivers and data processing software, which, before broadcasting the correction message, perform numerous checks to assure the message does not contain misleading information. Should they detect such information, the LAAS ground system must alert the air crew within six seconds in Cat 1 operations, within about three seconds for Cat II operations, and within about a second for Cat III operations.

Assured Cat III guidance also requires that at least four GPS satellites must be "in view" simultaneously. Often up to six satellites can be viewed; however if the signals from only four satellites can be received, there exists the risk of one failing just as an aircraft is at the critical stage of an approach. In this case, some persons in LAAS development have proposed pseudolites, which are ground-based GPS transmitters that replicate satellite-based transmitters. (The pseudolites would have to emit much less power than its spaced-base brethren to not overpower other radio signals in the airport area.)

Honeywell/Lockheed Martin

Honeywell, which has been working on LAAS development for years, made an agreement earlier this year to team with Lockheed Martin ATM, a long-time provider of air traffic control systems. Lockheed will assist Honeywell by providing logistics, training and field installations support for the LAAS Cat I program.

Honeywell established the first, and only, FAA-type certified Special Category I (SCAT-I) operation using an augmented GPS signal, in 1997. (A SCAT-I system involves the certified use of a ground system and an airborne system produced by a single manufacturer.) One Continental Airline aircraft was equipped to use LAAS-like systems installed at Newark and Minneapolis airports. Succeeding generations of Honeywell systems, called beta LAAS, have been developed, including the SLS-2000 and then the SLS-3000, which has a 48-channel receiver and multipath antenna to assure as little signal reflection from nearby obstructions as possible. "We’ve done a lot of study on multipath," says Hoodspith.

In the United States, Honeywell ground systems have been installed in: Minneapolis; Chicago (O’Hare and Midway airports); Newark (PANY), Memphis; Jackson Hole, Wyo.; Deer Valley, Ariz.; Moses Lake, Wash., with Boeing; Cedar Rapids (where Rockwell Collins is working on a multimode receiver that receives LAAS signals), NASA in Florida and White Sands, N.M; and Seattle. Systems exist in Frankfurt, Germany, and Malaga, Spain, and in 2003 Honeywell plans to install a ground system in Toulouse, home of Airbus.

Interestingly, Australia is considering a nationwide, LAAS ground-system network would provide en-route and terminal area navigation, according to Hoodspith. Called a ground-based regional augmentation system, or GRAS, it would use repeater stations to transmit correction messages out as far as 200 nm.

Applying Cockpit Expertise

Why has Honeywell, well known for its cockpit avionics, entered into ground systems development? "We are among the few companies with the expertise in flight-critical software," replies Hoodspith. "All our processes and configuration management and the way we do business is developed around the very stringent DO-178B spec for certification, and we believe that’s a benefit for LAAS development. For our early ground stations, we use our GPS receiver technology and the flight safety-critical software from our triple seven [Boeing 777] processors."

Honeywell also is working on an airborne multimode receiver (MMR) with LAAS capability, which will compete with an MMR developed by Rockwell Collins.

Raytheon and Thales

Raytheon and Thales, once competitors for the LAAS contract, formed a joint integrated product team in June, to "take advantage of two strong technologies and produce a winning product," says a Raytheon official. Both companies, like Honeywell, have long been working on LAAS development.

Having won a U.S. military advanced requirement definition (ARD) contract in 1999, Raytheon has been working on a parallel program, developing the Joint Precision Approach and Landing System (JPALS). The company also produced a shipboard version of JPALS for test and evaluation, which it delivered to the Navy in early 2000, and a portable ground unit for the Air Force, delivered in 2001. The contract was completed in early 2002, says Katanik, "but we’ve just received a contract for additional testing." The U.S. military "is trying to remain in sync with the civil community," he adds. The military variant is comparable to the civil LAAS but also includes encryption and advanced anti-jam capabilities, says Katanik.

A FedEx Boeing 727 equipped with the Collins MMR flew fully automatic (with the LAAS signal coupled to the aircraft) landings using a Raytheon LAAS system installed at Salt Lake City airport and using a JPALS system at Holloman Air Force Base, N.M. Likewise, Boeing has landed a 737 using LAAS guidance from the Raytheon ground station. Raytheon also has led one of the FAA’s LAAS GIP teams since 1999 and is the FAA’s prime contractor on the WAAS program.

No Stranger to LAAS

Meanwhile, Thales ATM, no stranger to LAAS technology, claims to have begun development in the area in 1992. It didn’t enter the FAA’s GIP program until June 2001, however, "when it looked like the specs [for LAAS] and the market were firming up," says Mark Boguski, Thales ATM’s director of sales and marketing.

Thales has had a ground system installed in Toulouse since 1999 for evaluation by Airbus and STNA (the French aviation authority). The company gained significant experience in precision landing system as a result of acquiring Shawnee, Kan.-based Wilcox Electronics, which has been producing ILS systems for nearly 40 years. The company also produces NDBs and ADFs, and developed a microwave landing system (MLS). FAA recently contracted with Thales to supply 375 new, low-power DMEs.

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