Found this at Boeing.
Boeing 757 Now Serves World's Highest-Altitude Airport
SEATTLE, May 1, 1995 -- A China Southwest Boeing 757 has inaugurated regular service to the world's highest-altitude commercial airport at Bangda, Tibet, from Chengdu, Sichuan, in the People's Republic of China, the Boeing Commercial Airplane Group announced.
"With minor changes to the cabin pressure system and flight operations procedures, the 757 high-performance twinjet is perfectly suited for Bangda," said John Chien, Boeing Sales Director, aboard the historic inaugural flight last week.
The 757, piloted by Zhang Kefu and Hu Yilian, left Chengdu at 8:00 a.m. with 100 passengers aboard. It was greeted at Bangda by airport officials and by Tibet Autonomous Region government officials.
At 14,219 feet (4,334 metres), Bangda Airport is the world's highest -altitude airport. Taking off and landing at Bangda is like operating from the summit of Mt. Whitney, 14,494 feet (4,418 meters) in California, which is the highest point in the 48 contiguous United States.
Boeing, the Civil Aviation Administration of China and China Southwest Airlines completed an important 757 survey flight to Bangda in October, 1994, to prepare for regular service. Additionally, Boeing and the airline recently used flight simulators in Seattle and Zhuhai, Guangdong, China to prove flight procedures and complete flight training, including single-engine take-off and landing.
Previously, people traveling west from Chengdu, gateway from central China to Tibet, had to travel three to five days by road to reach Changdu, a city and region of 500,000 between Chengdu and Lhasa. The trip by air now takes one hour. China Southwest began regular weekly service on April 30, departing Chengdu in the morning and returning in the afternoon.
In addition, Boeing 757s fly twice daily to Lhasa, Tibet, whose Gongga Airport is third highest at 11,621 feet (3,542 metres). The Boeing 757 and 767 were also the first modern twinjets to demonstrate engine-out take-offs and landings at Gongga Airport in 1991 and 1993 respectively.
Do they still fly there? Does anyone still fly there?