Flying a plane over the "roof of the world" is no easy task.

High terrain and severe weather once made Tibet, with an average altitude of 4,000 meters above sea level, off-limits for aircraft.

Stories of daring American pilots in the 1940s who flew along the Hump Route over the Himalayas to transport military supplies still resound. More than 500 aircraft and 2,000 pilots were lost to the mountains during World War II.

As Tibet marks the 50th anniversary of regular flights this year, aviation professionals explain how the industry has transformed life on the plateau.

50 YEARS: LEAPFROG DEVELOPMENT

Gyazhugling Village in Lhasa, capital of Tibet, is a perfect example of how planes can change lives.

Located just outside Lhasa Konggar Airport, Gyazhugling was once wild marshlands with only a few herdsmen. Since 1966, it has grown into a community of 1,000 residents, with two schools, a clinic, and a cluster of hotels and supermarkets.

With a 4,000-meter runway, Konggar airport transports thousands of passengers every day. For many tourists, Gyazhugling is their first stop.

Tibet now has five airports, one in Lhasa, and another four in Shigatze, Chamdo, Nyingchi and Ngari, which operate 58 flights to other Chinese cities, and also to Kathmandu, capital of Nepal.

In the past 50 years, Tibet's airports had 206,000 takeoffs and landings, and a total of 24.71 million passengers and 330,000 tons of cargo have been transported via the region.

Planes have brought tourists, boosted spending, carried agricultural produce to buyers thousands of miles away, and provided medical evacuation for herdsmen who live in the plateau hinterlands.

Aviation officials who have witnessed these changes credit the progress to strict attention to aviation safety and heavy investment.

In 1955, the Central Government decided to open an air route between Beijing and Lhasa, but it took another decade to make the flight happen.

"I remember there were endless tests and training. No one dared to put a plane and passengers over Tibet unless it was 100 percent safe," said Li Shunhua, former Party Secretary of the Tibet Civil Aviation Bureau.

Li recounted the challenges: heavy clouds, thunderstorms with turbulence severe enough to damage aircraft, sand and dust that could lower ground visibility to zero, and a lack of oxygen for ground staff.

"In the 1990s, there were sandstorms every afternoon in Lhasa. We had to plant thousands of trees around the airport to keep the air clean," said Li, who headed the bureau during the period.

The first flight from Beijing to Lhasa was made by an Il-18 aircraft on March 1, 1965.

"Over the decades, people working in aviation in Tibet have made great contributions and sacrifices to ensure the industry's safety and development," said Li, adding that better navigation technology also improved safety.

Aviation helped Nyingchi, in eastern Tibet, earn 1.11 billion yuan (177 million US dollars) in tourist revenue last year. The figure jumped 11 times compared to the number ten years ago.

"Tibet's tourism, express delivery and other industries wouldn't have flourished if it were not for the air connections," said Li Hancheng, the current director of the Tibetan aviation bureau.

GROWTH BRINGS CHALLENGES

According to a national plan for Tibet's development, in the next five years, the number of flights between Tibet and other cities will increase to 95. Annual passenger volume will reach 6.6 million by 2020.

Officials told Xinhua that passenger volume has reached twice the designed capacity at Konggar and Nyingchi airports.

"The infrastructure is in urgent need of further expansion and upgrades," Li said.

"Brain drain" is also a challenge. Dissatisfied with harsh work conditions, some pilots and airport staff have chosen to work elsewhere.

"It takes at least eight years to train a seasoned captain, because we have stricter requirements for flying the Tibetan route. We need to recruit experienced pilots to expand business," said Bai Weisan, vice manager of Tibet Airlines.

"We will improve wages for staff to keep them working here," he said.