Robert Burtt and Wilfred Moore, the duo who had come up with Captain Midnight, created Sky King in 1946 for the radio, basing it on a story by Roy Winsor. Sky King was an Arizona rancher and airplane pilot who stopped the bad people and rescued the lost people into 1954, when the radio episodes began playing concurrently with the television show. Sky's Cessna airplane was called The Songbird. His niece Penny (actress Beryl Vaughan) and nephew Clipper lived with him, both of whom were budding pilots.
(I never heard the radio show but I was a big fan of the television version when I was a kid. Like so many others, I was totally smitten with the cute, blonde Penny -- played by Gloria Winters; and I was saddened when the actress died seven years ago at the age of 78.)
To give you a taste of the radio show, here's two ten-minute episodes: "Prince Aron Zibi" from June 30, 1947, and "Army of Blue Men" from July 14, 1947. The announcer is a young Mike Wallace.