Learning to tango

New satnav routes pay off for GA pilots

March 1, 2009

OPA’s multi-year bid for RNAV terminal transition routes, also referred to as tango or T-routes, is beginning to pay big dividends for the general aviation community. These new pathways in the sky are now available in numerous U.S. locations, and more T-routes are in the works.

T-routes give pilots the ability to file and fly direct IFR routings around or through busy Class B and C terminal airspace, and in remote areas where the fixed locations of VORs, NDBs, and other ground-based navaids make direct routings unlikely or impossible. T-routes do this without increasing the workload of air traffic controllers, and come with a key safety benefit as well.

“With GPS guidance you’re not tied to high terrain for the sake of signal strength, so T-routes allow for lower minimum en route altitudes than conventional airways,” says Peter Lehman, AOPA’s manager of air traffic services. “Lower MEAs are a definite push in the direction of safer IFR flying, since they often allow pilots to stay out of the icing conditions associated with flights above the freezing level.”

The long way around

AOPA’s T-route odyssey began in the 1990s, when members began voicing frustration with the often wildly circuitous IFR route clearances they received when attempting to transit Class B airspace. In 2000, the association began discussing the issue with the FAA, and working groups with representation from both organizations convened to resolve technical issues and chart the way forward.

Initially called RNAV IFR Terminal Transition Routes (RITTRs), T-routes debuted in the Charlotte, North Carolina, airspace in September 2005, spreading to Cincinnati, Ohio, and Jacksonville, Florida, in December of that year. The next T-route appeared in August 2006—this one serves the Outer Banks region of North Carolina, replacing a conventional airway lost with the decommissioning of a hurricane-damaged, nondirectional beacon (NDB). T-routes have been created for Alaska, but are unavailable pending revision.

T243, the Outer Banks T-route, differs from the terminal area T-routes in that it’s far from any major city and its accompanying terminal airspace. It exists to give IFR traffic a safe pathway through a cluster of military operations and restricted areas located on the North Carolina coast. It also provides an airway link to the final approach fixes for nonprecision approaches serving two popular GA destinations—Hatteras and Ocracoke Island.

“The Outer Banks T-route shows how the program continues to evolve,” says Jim Arrighi, an air traffic specialist with AJR-37, the FAA’s RNP/RNAV working group. “We saw this as a perfect opportunity to replace an out-of-commission airway, and this sets a strong precedent for similar actions around the country.

“It also got us thinking—why not put GPS MEAs on Victor airways as well? That’s really where our emphasis has been in the past year. It’s a great idea, and can be implemented in many locations. To justify doing it, though, we’ve got to see a tangible benefit and for us, that means a minimum gain—a loss, really—of 500 feet.

“The lower MEAs also have to comply with standard TERPS criteria, just like any other IFR procedure. Although the reception of a ground-based navaid is no longer an issue, obviously, we still have to ensure a minimum standard of obstacle clearance and two-way VHF radio communications along the entire route.”

To use a T-route on an IFR flight plan, an aircraft must qualify for equipment suffix “slant golf” (/G), meaning it must be equipped with a panel-mounted, IFR-certified GPS receiver. And the pilot must be instrument rated and current. There is no specific prohibition against flying a T-route in VFR conditions using a portable GPS unit for track guidance.

For flights above 18,000 feet, the FAA has implemented a number of Quebec or Q (pronounced as the letter Q) routes; these have appeared on the West Coast, over Texas and Florida, and in the Boston area. Canada has embraced the concept as well, and Q-routes are becoming more common north of the U.S. border. While the Q-routes aren’t quite as far along as T-routes, Arrighi is confident that they will become just as prevalent.

“We recently started an initiative to re-invigorate the high-altitude RNAV effort,” he says. “Our intention is to connect the dots, although they’re pretty far apart at the moment.”

GPS and the future

While GPS has revolutionized air navigation, the system remains vulnerable to external forces, such as satellite outages, intentional jamming, or a political decision to turn off the system or degrade its performance. The GPS is, of course, reliant on the Navstar satellite cluster—a U.S. Air Force program—and is therefore subject to influences far beyond the civil aviation realm. With this situation in mind, the FAA and other groups are actively pursuing a back-up strategy.

In 2007, the FAA made the decision to begin phasing out VOR service in favor of satnav, but the agency is still determining just how many VORs to keep operational over the long term. The first large-scale shutdowns are not expected until 2011, and a “decision on further discontinuance,” the FAA said, is unlikely to occur before 2015.

GPS alternatives under consideration include RNP-based DME/DME updating and maritime-focused eLoran systems, but further development seems unlikely without a commitment from senior FAA management. Other government, industry, and academic groups that assist the FAA in modernization work, including RTCA, Mitre Corp., MIT’s Lincoln Labs, and the Johns Hopkins University Applied Physics Lab, could influence the final strategy.

For now, AOPA is carefully considering these proposed alternatives, but views the VOR network as an adequate GPS backup. “Our members are encouraged to buy additional boxes if they think it will enhance safety, but we will always oppose any unnecessary equipment mandate,” says Randy Kenagy, AOPA government affairs chief of staff. “Any talk of a comprehensive VOR drawdown is premature, as long as the FAA still requires our members to carry a VOR in an aircraft that already has an IFR-certified GPS receiver.”

As for the GPS, it’s poised for a major upgrade. In May 2008, a Lockheed Martin-led team edged out incumbent Boeing for a $1.4 billion contract to develop
the next generation of GPS satellites, known as GPS III. This new satellite constellation will be built to resist jamming, with faster clock update rates providing improved accuracy. These satellites—32 in all with an initial launch planned for 2014—are also expected to have 500 times more transmission power than the current generation.