HIMALAYAN RNP

The first required navigation performance approach into this new airport in a mountainous valley is a sign of things to come as China plans to certify up to 50 more RNP procedures at terrain-challenged airports in a five-year period.

RNP procedures use advanced flight management systems and satellite navigation primarily (though in some cases DME-DME) to allow airline aircraft to drive down tightly confined corridors of airspace. Airlines and ATC agencies worldwide are starting to embrace this type of "performance-based" navigation, and China is poised to implement it on a large scale. For this RNP approach in Tibet, an Air China Boeing 757 was relying on dual GPS receivers, flight path computers and inertial reference systems so no single failure could cause a loss of navigation capability. Self-monitoring avionics systems are installed to alert pilots of any problems.

This Aviation Week & Space Technology pilot observes parts of the approach into Linzhi from the cockpit. The RNP procedure we are flying was developed by Naverus Inc. of Kent, Wash., a 50-employee company. Steve Fulton, chief technical officer of Naverus, and Buzz Nelson, who joined the company after a 31-year career as a Boeing test pilot, also are on the flight.

The recently completed 9,700-ft.-elevation Linzhi Airport is ensconced in a valley with a ridge jutting out to the left toward the approach path to one end of the 9,800-ft. runway. The RNP approach to Runway 05 curves to the right to avoid this ridge. But RNP is very precise and the aircraft we are on is equipped with Honeywell Pegasus flight management systems and Rockwell Collins multi-mode receivers. The avionics suite uses GPS receivers to fix our position within 3-4 meters (10-13 ft.). Fulton notes this type of accuracy has been routinely possible since 2000 with the unaugmented GPS constellation, now that the U.S. allows all users to access precise signals.

Air China pilots believe the Tibetan terrain poses the most challenging mountain flying in the world. Departing Chengdu Shuangliu International Airport on Sept. 1, we are soon above the Tibetan Plateau, called The Roof of the World, headed into an area of 25,000-ft. mountains.

Li Jun, the vice minister of the General Administration of Civil Aviation in China (CAAC), is on board for this first revenue flight into the new airport at Linzhi. He notes that the approach to the airport "requires very accurate navigation" and the valley has "very tricky weather--lots of low clouds and rain." On this day, however, it is, as pilots say, "clear and a million"--a rarity here--making it possible for us to see the dramatic terrain, including snow-capped mountains.

Our 757 will be using GPS guidance, but the Chinese also are working with the Europeans to use Galileo satellite navigation on aircraft in the future. Li notes that there is no radar coverage on our route into Linzhi. In addition, ground-based navaids are few in number and limited by line-of-sight.

In China, 40-50 airports, mostly in Tibet and the southwest region, will have RNP in the next five years he says. This could even put CAAC and the Chinese Air Traffic Management Bureau (ATMB) on a faster pace of RNP implementation than the FAA in the U.S. Li notes that China has more requirements for these types of procedures in part because it is building so many new airports. The CAAC may employ it at such congested sites as Beijing or Shanghai to facilitate efficient ATC operations. "We may need RNP to solve some traffic problems," says Cheng Yi Ru, senior vice president of flight operations for Air China.

Capt. Wei Yi Qiang, director of flight standards for Air China Southwest, is at the controls with Capt. Tang Jian in the right seat. Air China policy calls for both pilots on revenue flights to be experienced captains and to have flown qualifying trips into airports in Tibet. Several decades of accident-free flying into Lhasa proves the wisdom of this. On the revenue flight there are six paying passengers along with officials from the airline, CAAC and ATMB.