Honeywell has completed a series of GPS-guided autoland approaches to each of the four runways at Moses Lake Airfield in central Washington using a single Honeywell/Pelorus local-area augmentation system (LAAS) ground station. The successful trials, conducted over a 45-day period that ended in January, come just as
the FAA is preparing to award a major contract for the supply of 60 Cat I LAAS ground stations through 2007.
LAAS eventually will replace all categories of ILS as the preferred precision landing aid at many U.S. airports. Full-scale engineering development of LAAS is scheduled to get under way this year, after which procurement of LAAS ground equipment and installations at selected airports will begin. The competitive bid process is scheduled for this spring, and is to be followed by an FAA contract award by July.
LAAS allows properly equipped aircraft to fly complex, curved approaches to avoid residential areas while maintaining safe separation of aircraft. The LAAS station on the ground at an airport monitors signals from GPS satellites, checks them against its own surveyed location and broadcasts correction signals to aircraft equipped with LAAS-capable avionics.
Similar demonstrations of the Honeywell/Pelorus LAAS ground reference station were completed at Chicago O’Hare International in November and Memphis International Airport in Tennessee last March, where FedEx flew a Boeing 727 to test a series of precision approaches and autoland procedures.
Honeywell officials expressed satisfaction with the results of the Moses Lake tests.
“All landings were extremely steady and stable, accurate and fully consistent with preflight expectations,” said Ed Wheeler, vice president of Honeywell Airport Systems. “LAAS signal reception and strength were extremely good. Stability and smoothness of each approach appeared significantly better than currently experienced with conventional ILS.”
LAAS systems built by the Honeywell and Calgary, Canada-based Pelorus team and others are currently in operation for VFR-only approaches at Chicago O’Hare and Midway; Memphis; Cedar Rapids, Iowa; Salt Lake City; and Kansas City, Mo. FAA type acceptance of these initial ground stations is expected late next year or in early 2004.
The first Cat I-certified installation of a LAAS ground station is expected next year. The agency plans to purchase 60 Cat I LAAS units in all, which will be delivered between 2004 and 2007 and installed primarily in mountainous or other locations where Cat I WAAS guidance may be unreliable. The FAA’s Cat III LAAS plan calls for the first installation entering service in 2007, followed by a further 114 units, installed at a rate of 20 per year, at airports across the country.
The threat of accidental or deliberate GPS signal interference, however, continues to worry FAA officials. A study of GPS vulnerability, prepared by the DOT’s Volpe Technical Center in Cambridge, Mass., three years ago, was released late last year. Essentially, the Volpe report examined the full range of GPS vulnerabilities, from natural disturbances to intentional signal disruptions, all of which could potentially cause temporary or longer-term loss of signals.
The report stated that the most critical GPS deficiencies were its extremely low-powered signals and its single civil frequency. These deficiencies, it said, would be corrected in the DOD’s GPS III, which will transmit at higher power over two dedicated civil frequencies, thereby virtually eliminating natural interference and thwarting inexpensive, pocket-sized GPS signal jammers. However, the report noted that GPS III is not expected to become operational until between 2012 and 2015 (see related article below).
Until then, GPS remains “extremely vulnerable” to interference, and the Volpe Center therefore recommended a comprehensive analysis of GPS backup navigation and precision-timing options, including VOR/DME, ILS, loran-C, inertial navigation systems and improved operating procedures, which could be used in conjunction with LAAS to ensure the veracity of GPS signals.