Burlington Northern formed a cargo airline known as Burlington Northern Airfreight in 1972, which was sold to the Pittson Company in 1982, changed their name to Burlington Air Express in 1986, and rebranded to BAX Global in 1997. They were sold from Brink's (formerly the Pittson Company) to DB Logistics, aka Deutsche Bahn in 2006. In 2011, DB decided to cease operations of BAX Global. Technically, it means the great Burlington Northern didn't go defunct until 2011, in a way. 

In 1937, the Canadian government formed Trans-Canada Air Lines, as a subsidiary of Canadian National, which would become Canada's main carrier. In 1965, TCA became Air Canada, and in 1976, with CNR's reorganization, Air Canada would become it's own crown corporation, and still exists today as the biggest airline in Canada.

Canadian Pacific would end up feeling threatened by the creation of TCA, and bought 10 bush airlines in the early 1940s, finishing in 1942, forming Canadian Pacific Air Lines. Canadian Pacific Air Lines would rename themselves to CP Air featuring the Pac-Man logo (or the Multimark, as boring people call it) in 1968, but would go back to Canadian Pacific Air Lines in 1986. In 1987, Canadian Pacific Air Lines, Nordair, and Pacific Western Airlines would merge to become Canadi›n Airlines. Ironically, Canadi›n Airlines was acquired by Air Canada in 2001.

In 1946, the Atchison Topeka and Santa Fe formed an airline known as Santa Fe Skyway. The airline lasted a very short time, as in January 1948, the Civil Aeronautics Board denied their application to become a common carrier due to a policy barring railroads from owning airlines. (BAX got around this by their aircraft being operated by ATI, not directly by BAX.)

A little bonus, Guilford Rail System bought the rights to Pan American World Airways in 1998, and rebranded as Pan Am Railways in 2006. However, they had no relation to Pan Am other than buying their name. They merged with CSX in 2022.

These 4 airlines were made by railroads!