The Planet, the airliner which took centre stage in Night Flight, was obviously a fictional aircraft. Johns could not very well put the scare up the public by suggesting that a real aircraft type or one belonging to a real airline had been going missing. Some of his readers might take it seriously. He might have used a real aircraft type like he did with the Douglas DC-3 in Dangerous Freight but this was a freight aircraft and a freight company. Moreover the DC-3 was an old and established aircraft. In Night Flight the focus was on a new aircraft being stolen for possible use behind the Iron Curtain.
Johns doesn't describe the Planet. It is just possible that the Planet might have been inspired by the de Havilland Comet--note the similarity in astronomically based names. Furthermore, three Comets crashed between May 1953 and April 1954 under mysterious circumstances. The story was published around this time and the entire story might have been inspired by these events. Of course, Johns couldn't make the connection too obvious. Nowhere does Johns suggest that the Planet is a jet aircraft. Throughout the text, there is the constant mention of the "drone" of the engines--not jet sounds.