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Online Extra

RNP Approach Provides Access to Remote Tibet

Imagine flying to an airport that’s 9,670 feet above sea level sandwiched in a river valley between jagged peaks soaring up to 20,000 feet and usually shrouded by fog or overcast.

Many aviators consider Lin Zhi airport—one of many in Tibet—to be the world’s most challenging approach. While other Tibetan airports—such as Lhasa Gonggar, at 11,811 feet, and Chamdo Bangda, at 14,219 feet—are higher, the geography surrounding Lin Zhi is far less forgiving.

Lin Zhi uses Required Navigation Performance (RNP) technology to get aircraft in and out safely. The airport became prominent when an Air China Boeing 757 using RNP first flew into Lin Zhi in September 2006 to a rousing reception.

RNP technology locks the aircraft into a three-dimensional flight path created by the FMS and an RNP database, enabling the aircraft to descend a defined path of gentle curves. The Lin Zhi approach, however, contains a 90-degree turn and a 90-mile missed approach to ensure obstacle clearance, as well as an added turn just before final, according to designer Steve Fulton of General Electric, who worked for Naverus, the company hired by China to install the approach. On the Runway 5 approach, “wings level isn’t achieved until 200 AGL,“ he noted. Naverus was recently acquired by General Electric.

An ILS was first installed, but it was so risky, the test aircraft’s “wheels never touched the ground,“ noted Andy McDowell, Jeppesen’s director of airspace and airports. “Without RNP, you need VFR to get in.“ That long missed-approach leg, McDowell added, is designed to get an aircraft above the mountains on one engine.

“The current minimums in Lin Zhi are based on RNP 0.30,“ said GE’s Fulton. “There’s a large number of aircraft in China capable of RNP 0.10, and I expect that in time we will see lower minimums at the RNP airports.“

With 105 waypoints, the approach can tax even the best FMS systems, said Pat Dunn, the managing pilot for RAC TransCorp, who has extensive experience flying in Asia. While RNP approaches offer greater accuracy and more economy since ground-based infrastructure isn’t needed, it will take more than cutting-edge technology before flying into China and particularly Tibet becomes routine.

Satisfying the gauntlet of bureaucratic hurdles, permissions and clearances is a nightmare, according to Dunn. “There are few operators going into Nepal, much less Tibet,“ he said. “The procedures are so onerous that few corporate operators feel the trip is worth it.“ Moreover, in a region where the military has traditionally controlled all airspace, Lin Zhi is still a “closed airport,“ open only to Chinese operators, added GE’s Fulton.

For those who manage to fly into Lin Zhi, the Chinese require a local navigator to be on board to assist with the approach and the language. Aircrews are also required to practice the procedure in a simulator, said Dunn.

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