LAAS could end up being overtaken by a combination of the FAA’s WAAS and Europe’s GPS equivalent, Galileo. While official speakers at last month’s U.S. Institute of Navigation satellite navigation conference in Portland, Ore., avoided directly questioning the future of LAAS, there were enough pointers in their formal presentations, coupled with informal discussions with industry attendees, to suggest that the FAA’s local-area augmentation system for Cat I GPS approaches might be stillborn, superseded by “foreign” signals from space.
Galileo is being developed by the Europeans as a worldwide, 30-satellite system whose signals will be identical to those of GPS, and will therefore complement the U.S. system. But being a more mature system–GPS is now in its 30th year–Galileo will incorporate newer technology and is expected to offer greater accuracy and integrity when it enters service around 2008.
(For precision approaches, a single LAAS ground station would serve all of an airport’s runways.)
According to some industry experts, WAAS and Galileo could provide NAS-wide Category I approaches several years earlier than the FAA’s current LAAS implementation plan, and in doing so save the cash-strapped agency a substantial investment. In fact, it was suggested that combining Galileo with WAAS or its EGNOS or MSAS equivalents in Europe and the Far East could provide Cat I precision approach guidance to virtually every runway in the northern hemisphere, and conceivably 10 years or more before LAAS becomes available in most overseas countries.
And this mix ’n’ match of U.S. and foreign satnav capabilities exemplifies the future “seamlessness” of air navigation as we move further into the 21st century, and into an era where electronic frontiers cease to exist, and where transitioning from one system to the next will be transparent to pilots.
Commissioned by the FAA in July, WAAS geostationary earth orbit (GEO) satellites appear to hover at 24,000 miles above widely separated locations along the equator, where they transmit to users failure warnings and accuracy corrections for the GPS satellites orbiting the earth at 11,000 miles altitude. The European EGNOS and the Japanese MSAS will perform similar functions over their regions and will link with WAAS to cover the entire northern hemisphere.
WAAS today can support LPV (localizer precision with vertical guidance) approaches in IMC down to as low 250 feet and half-mile visibility in some cases. But this is still above the true 200-foot Cat I offered by ILS, mainly due to errors caused by small but unpredictable shifts in the ionosphere that distort the incoming satellite signals. To overcome this, each satellite must transmit its signals on two different frequencies, called L1 and L5, which are then compared by the aircraft’s receiver, and any differences between them are used to cancel out the errors.
However, the current GPS satellites transmit only on L1, although the DOD’s planned new-generation replacements will offer L1 and L5 and a number of other improvements. Unfortunately, those future satellites are many years away, since the DOD replaces failed satellites on only a one-by-one basis. As GPS industry pioneer Charles Trimble told conference attendees, “The good news is that the satellites are lasting much longer in space than forecast. The bad news is the same: they’re lasting much longer.” Ray Swider of the DOD noted that nine of the present 23 GPS satellites in orbit were still fully operational well past their predicted seven-year lives. In fact, one is entering its 14th year and still going strong. Consequently, some conference attendees felt it unlikely that a complete, L1/L5-capable GPS satellite constellation would be operational much earlier than 2020.
This is where Europe’s Galileo could come in. Among its technology improvements, every Galileo satellite will cover both L1 and L5, which means, according to the concept’s proponents, that by around 2010 every qualifying runway in the U.S. could offer a WAAS/Galileo Cat I approach.
The issue would then turn on political, rather than technical, grounds. That is, would the U.S. approve the use of a foreign satellite system to fly Cat I approaches in the NAS? It’s a delicate question. Other nations accept the use of our “foreign” GPS in their airspace.
And some government bodies, notably the State Department, still regard Galileo as an unwelcome intruder onto what they believe is exclusively U.S. turf. But this view is slowly changing. The DOD’s Swider stated that Galileo’s increased accuracy and integrity will offer a “vast improvement” in civil service.