Thanks bel,
The plane receives the transmission, which is sent by the radio controller in the hands of the person on the ground. When planes lose radio contact, the flaps etc. would all return to a neutral position and they just keep on going in whatever direction they were headed at the time. What the author, me, is trying to say, is that they often crashed into an oak after losing radio contact.

Does read better?
“Sometimes they’d get out of range of the radio signal, and wouldn’t respond to the transmitted orders. Once in a while they’d head north, with nothing between them and Canada to slow them down. Bye. Most times, when the planes were left incommunicado, they’d fly into one of the big oaks.”