He began his career with Pan Am in 1941 as Juan Trippe's private pilot, retiring in 1968 at the age of 50. While employed with Pan Am, Ueltschi married his wife Eileen in June 1944.
He founded FlightSafety International in 1951, the world's foremost aviation training organization, after noticing that corporate pilots did not receive the same rigorous training as airline pilots had. His first endorsement came from Trippe, who was President of Pan Am at the time. Ueltschi stepped down as President of FlightSafety in 2003, yet remained Chairman. The motto he started with still remains with FlightSafety today: "The best safety device in any aircraft is a well-trained crew." Berkshire Hathaway acquired FlightSafety in late 1996.
In 2010, Ueltschi cofounded HelpMeSee with his son Jim, to address cataract blindness in the developing world by training thousands of cataract specialists using techniques developed by Ueltschi himself.
On September 18, 2012, Ueltschi signed The Giving Pledge, noting his commitment to cataract relief.