John Walton, the second son of Wal-Mart Stores Inc. founder Sam Walton and Wal-Mart board member, died on Monday in a plane crash, aged 58. The billionaire was piloting the small plane near his home in Wyoming when it crashed shortly after take-off.

Walton was an experienced pilot and a former Special Missions operative in Vietnam. He lived in Jackson Hole, Wyoming. At the time of his death he was flying a 400-500 pound homemade plane with an aluminium body, cloth-covered wings and a small engine, said Joan Anzelmo, a Grand Teton National Park spokeswoman.

Anzelmo said that the Federal Aviation Administration had declined to investigate the crash as it did not involve a registered aircraft. Instead, park rangers were looking into the incident. In a statement, Wal-Mart said that the cause of the crash has not yet been determined.

Walton ranked 11th on the Forbes magazine's most recent list of the world's richest people. His net worth was estimated at $18.2 billion. During the Vietnam War he was awarded a Silver Star for helping to save the lives of several unit memebers while under enemy fire. Walton was an enthusiastic philanthropist during his lifetime and pursued a variety of business interests. Most recently, he established the holding company True North, which was composed of businesses ranging from boat building to venture capital investments. From July 1983 to March 1994 he as the chairman of Corsair Marine Inc.

"This is a horrible tragedy. What is so unusual about this is it is the founder's son," Bill Dreher, a Wal-Mart analyst at Deutsche Bank told Reuters. "Sam Walton was brilliant with estate planning. I don't know all the details with John Walton, but I would expect there woud be a smooth transition." As a board member, Walton served on the board's strategic planning and finance committee. He and the rest of his family owned approximately 40 per cent of Wal-Mart shares through Walton Enterprises, LLC.