The FAA says airlines may be able to begin using ground-based augmentation systems (GBAS) for satellite-based Category 3 instrument landings that culminate in a 50-ft. decision height or an automatic landing by 2018, offering a lower-cost alternative to legacy ground-based instrument landing systems (ILS).

A growing number of carriers are beginning to use the equipment for Category 1 instrument approaches with a 200-ft. decision height at a handful of airports, including Newark, Sydney, Frankfurt and Houston—an interim step before Category 3 operations as the industry gains experience with the technology.

Compared to a legacy ILS—which requires localizer and glideslope transmitters at each runway end—one suite of GBAS equipment can provide approaches to 26 runway ends while offering a choice of glidepath angles and touchdown zones. The GBAS built by Honeywell for Newark and Houston uses four GPS receivers on the ground for redundancy and to reduce the effect of signal noise through averaging. GBAS requires a multi-mode receiver on the aircraft to pick up GPS-correction factors sent up on VHF links from ground-based receivers that compare the raw GPS position to known positions of the receivers, to compute errors introduced by the ionosphere and other factors.

Delta Air Lines conducted its inaugural GBAS landing with a Boeing 737 at Newark on Feb. 18, joining United Airlines and British Airways (BA), which were already flying the approaches there.

United is averaging 65-70 GBAS landing system (GLS) approaches at Newark and Houston’s George Bush Intercontinental Airport each month with a portion of its Boeing 737 and 787 fleets, which come with GLS avionics as standard equipment. United has more than 95 737s and 14 787s with GLS avionics, and is selecting the option for all newly delivered 737s. BA is flying GLS approaches with its 787s into Newark.

Delta is using the approaches in Houston as well as in Newark, and has a fleet of more than 42 GLS-equipped 737s. The carrier is investigating GLS for its Airbus fleet as well. In total, the airline plans to have 177 aircraft equipped for the approaches by 2019, according to the FAA.

A growing number of foreign airlines also are using the capability at Newark and Houston. Emirates conducted its first GLS landing in Houston in December with an Airbus A380, one of 57 GLS-equipped A380s at the time. The carrier also uses the approaches at Sydney, Frankfurt and Zurich. And Lufthansa made its first GLS landing in Houston in December with one of 12 equipped A380s that also use the approaches in Sydney and Frankfurt. Cathay Pacific made its first GLS landing in Houston, with a Boeing 747-8, at the end of January. The FAA says Virgin Atlantic is also planning to seek operational specification approval for the approaches into Newark. Other foreign carriers purchasing GLS-equipped aircraft include Air Berlin, Qantas, Swiss Air, TUIfly and various Russian airlines, the FAA says.

Boeing says it has more than 1,000 GPS-equipped in-service aircraft, with the number growing by 25 per month. The airframer says one-third of all new 737s are being delivered with the option, which is standard equipment on the 747-8 as well as on the 787.

Flight-testing on GLS for Category 3 approaches, which include autoland capability, continues at the FAA’s Technical Center in Atlantic City, New Jersey, and in Europe through the Single European Sky ATM Research (Sesar) program in Toulouse, France, and Frankfurt.

As part of its research last year, Boeing completed 12 Category 3 GLS autoland approaches with its 787 “ecoDemonstrator” at the company’s Moses Lake, Washington, facility, a location that also uses a Honeywell GBAS.