The Federal Aviation Administration (FAA) insists that its decision earlier this month to lower the altitude for allowable approaches using the Wide Area Augmentation System (WAAS) from 250 ft. to only 200 ft. above an airport’s surface was done in full consideration of the safety concerns.
But a knowledgeable observer of FAA’s actions through the years, who wants to remain anonymous, believes the agency waived its own safety standards in lowering the WAAS minimum. FAA has a lot invested so far in WAAS development, he explains. The agency not only wants to expand its use, but have WAAS actually replace the use of instrument landing system (ILS) approaches at more airports.
FAA commissioned WAAS in 2003 to improve the signal accuracy of the Global Positioning System (GPS) satellites. WAAS is generally thought to improve accuracy of GPS signals by a factor of 5 — down to about 3 meters. Initially, WAAS was intended for all civilian craft, but commercial airlines today mostly use ILS to make Category 1 (200 ft.) approaches. This leaves WAAS as the precision-approach method of choice for regional carriers and general aviation, who often have no other option at smaller airports.
Not wishing to “respond directly to Mr. Anonymous,” Dan Salvano, FAA’s director of navigation services, declares to Air Safety Week, “This is not something we did to meet some users’ expectations.”
For one thing, after looking at about 1.8 billion data points over the last couple of years, the FAA concluded that WAAS signals met or exceeded its requirements for their designed use. Also, in flight tests, WAAS was just as satisfactory as ILS. Taking into account such things as the variations in pilot skills and the range of altimeter readings, FAA’s analysis showed that WAAS still met the criteria of the ILS collision risk model.
Also, the new decision does not mean that 200 ft. is now okay for WAAS-guided landings in all situations, Salvano explains. In fact, it’s only okay if certain other conditions are met. Planes must have the proper avionics, pilots should have the proper training, the surrounding airspace and terrain needs to support its use, and airports must have the right infrastructure (particularly runways that are long enough and wide enough).
Furthermore, the FAA is working on even more system improvements. The current WAAS software, for example, operates a bit too conservatively, Salvano says, because it’s too ready to back off from using a precision approach. By way of illustration, he cites a solar storm that occurred around Halloween in 2003. The software’s algorithms detected that its parameters for safe use of a precision approach were exceeded. However, the agency also later saw that there had been no loss of the signal or of signal accuracy. The algorithms are now being worked on so that the software will still allow a precision approach in such conditions.
Also, in certain places in the United States, such as the northeast, southwest, and Alaska’s north slope, “the availability of the WAAS signal is not as high as we wanted it,” Salvano says. So, the agency its expanding the number of ground reference stations in Canada and Mexico. When this expansion is completed, there’ll be a true “North American WAAS system.”
The FAA also says that when it first commissioned WAAS, it “was approved to provide vertical guidance down to 350 feet.” Then, “localizer performance with vertical guidance procedures down to 250 feet was later developed to take advantage of the increased performance provided by WAAS.”
Our anonymous source says he’s “not entirely surprised” that WAAS has now been declared safe at 200 ft. That level has a certain status among pilots, mostly because it allows Category 1 precision approaches. He also tells Air Safety Week that he doesn’t think the FAA has necessarily made the wrong decision from a safety viewpoint. It’s just that there probably some other considerations. There likely was some ego involved in ensuring that WAAS could keep up with other technologies.
It’s even conceivable the agency might take some additional steps that force more pilots and operators to buy WAAS equipment, he adds. But such actions could create a strong backlash in the aviation community.
>>Contact: FAA public relations, (202) 267-3883<<
EU Says ‘Keep Out’
Last week, the European Union (EU) finally announced its “blacklist” of more than 90 airlines that will no longer be allowed into the airspace of EU member countries, due to pre-established safety criteria. The list has a disproportionately large number of carriers from developing nations, and especially carriers based in Africa, which has had more its share of recent and serious accidents. But many of the affected airlines currently do not fly to Europe. EU officials explained that creation of the list was partly an attempt to prevent future problems, and allow some carriers to improve their safety procedures. It also was intended to harmonize European restrictions, as several member nations had already taken it upon themselves to issue their own lists.
In a related development from its conference in Montr?al, the International Civil Aviation Organization (ICAO) said its member countries will publish their aviation safety records online. Originally, certain developing nations argued that such information should only be shared within ICAO. But the last vestiges of resistance were overcome when it was agreed that the information wouldn’t appear until two years from now.