John Walton, a billionaire heir of retail giant Wal-Mart, died on Monday (local time) when the small plane he was flying crashed in a national park in Wyoming, authorities said.

Walton's plane crashed at 12:20 pm local time (1820 GMT) shortly after taking off from Jackson Hole Airport in Grand Teton National Park, the National Park Service said in a statement. The cause of the accident was not immediately known.

"Walton, the pilot and sole occupant of the aircraft, died on impact and was later pronounced dead at the scene by Teton County Coroner, Bob Campbell," the statement said.

A park spokeswoman said Walton, 58, was an experienced pilot who was flying a home-made aircraft with an aluminium frame and wings wrapped in fabric similar to heavy-duty sail cloth.

"This was an experimental, very lightweight aircraft," said the spokeswoman, Joan Anzelmo. It weighed between 180 to 225 kilograms, she said.

The Park Service's statement described it as an "ultralight aircraft with a small, gas-powered engine."

Weather conditions were good at the time of the crash, Anzelmo said.

Walton, the second son of Wal-Mart founder Sam Walton, was the world's 11th richest person with a net worth exceeding US$18 billion, according to Forbes magazine.

He had been a member of Wal-Mart's board of directors since 1992 and lived in Jackson, Wyoming, a town known as a resort for wealthy Americans.

In a statement, Wal-Mart expressed sorrow over his death and described Walton as a Viet Nam War hero and philanthropist.

"As a board member of the Walton Family Foundation, Walton played a leading role in guiding the Foundations contributions to elementary and high school education, including scholarship programmes to provide parents with greater choice in education," it said.

Walton served as a medic in the US Army Green Berets during the Viet Nam War and was awarded the Silver Star "for saving the lives of several members of his unit while under intense enemy fire," the company said.

He worked as a crop duster in the 1970s and as a boat builder in 1980s and 1990s.

Walton formed the holding company True North, which includes businesses ranging from advanced composites to boat building to venture capital investments, Wal-Mart said.

He is survived by his wife Christy and their son, Luke; his mother Helen; and his siblings Rob, Jim and Alice.

Wal-Mart employs more than 1.5 million people around the world, with more than 3,600 stores in the United States and another 1,500 abroad, including China, the Republic of Korea, Germany, Brazil and the UK.

Source: China Daily