It was not just the first broadcast from an airplane, but also the first moving airplane. It wouldn't be much of a first if the plane was still on the tarmac. The claim seemed obscure possibly apocryphal. But it appears in both the book "Connecticut Firsts" and the 1966 edition of Cahners Broadcasting. If it's untrue at least we're consistent.
The year was 1926 and John Harper Trumbull, [R] governor of Connecticut was in the Air over Hartford broadcasting by shortwave. He was the 54th governor of Connecticut and known as the "Flying Governor." As the chairman of Colonial Air Transport he often flew into Robertson Field Airport in Plainville, CT. (This was decades before Bradley airport was built.) He was very media savvy for the era. He was the publisher of the Rhode Island Weekly Advertiser and very interested in this new radio thing.
560 WTIC-AM received and rebroadcast the live feed from shortwave. Travelers Insurance founded the station in 1925 with a license to operate at 500 watts. They became an NBC affiliate a year later. This was very early in the history of Radio for Connecticut. The first station in the nutmeg state was WDRC-AM in 1922. By 1928 only four other stations were on the air. WCAL-AM was a share time with WDRC-AM, WCWC-AM was s share time with WICC-AM, and WTIC-AM was a full-service operating out of Hartford. (weirdly in 1927 WCAC briefly was a share time with WTIC on 560 kc , then again at 600 kc )
WTIC moved to 600 Khz and bumped up the juice to 50,000 watts in 1929 on the first 50k transmitter ever made by RCA. It's serial number is actually 001. it used both the first first mercury-vapor rectifiers and the first 100-kilowatt tubes. In later years they shifted to 140 AM then 1080 where they presently reside. More here.
Governor Trumbull retired from public service in 1931. In 1933 he was sent as the Connecticut delegate to ratify the 21st Amendment repealing prohibition. So he may have been a republican but he wasn't all bad.He was buried in the West Cemetery in Plainville near the old airport.