How did 1950s transatlantic flights stay in contact with ground control?

[u/foraminifer]

Could commercial airplanes on transatlantic flights in the mid to late 1950s radio the airport/ground control - did they have that long distance communication, or was there a stretch of the flight where they'd be too far away to reach the airport? Did they have autopilot? (Basically I'm trying to figure out what they'd do if the pilots got sick.) Thank you, historians!

[u/Downtown-Act-590]

So on transatlantic flights, you would see two radio frequency bands used to communicate - HF and VHF.

VHF is the default in airplane radios. Even in 1950s, it was very reliable for carrying voice messages. However, it propagates mainly by line of sight. Due to curvature of Earth, you are then out of VHF comms over very large part of the Atlantic crossing. You can even calculate the distance to the ground station at which you lose contact using the radio horizon formula given that you know the altitude of your flight.

If you only had a simple message to the ground control though, it is very likely that you could reach another aircraft on VHF which would then relay your message to the ground. It would be rather troublesome to convey longer messages like this though as you don't speak directly.

So, that is why we use the HF radios. The radio waves in this frequency band refract from the ionosphere and as such they can be used to communicate beyond line of sight. That is a big advantage. It is however a lower frequency and as such it offers a lower available bandwith. That is a disadvantage as it reduces the information content you can put in.

Already before WWII, there was an interest in providing flying boats crossing the Atlantic with HF communications. For example famous Shannon Aeradio was founded in 1936 [1] and its no less famous counterpart in Gander on the other side of the Atlantic began transmitting in 1938 after moving there from Botwood [2]. Due to tricky nature of HF though, they didn't communicate through voice at first, but merely by Morse code and that continued until late 1940s [3].

The early voice communication over HF would not be excellent or very reliable either. Weather-induced noise, the muffled voices over the low bandwith... There was still a lot to be desired. Only well after 1950s we would reach the quality of HF radios we have today. You could very likely communicate with a ground station in a situation where one of the pilots got sick, but you probably would not have an enjoyable conversation.

Regarding the question about the autopilot. There would indeed be an autopilot, but it would have very different capabilities than autopilots of today. Majority of the propeller airliners which did the bulk of work over the Atlantic in the 1950s would have rather primitive gyroscopic autopilots mostly useful to stabilize the aircraft in straight flight. The early jets like the Boeing 707 would be no different and its Bendix PB-20 autopilot would maintain steady straight flight, turns or climb/descent [4]. Importantly, autolanding came only a decade later on a British Trident jet in 1965 [5].

So as a conclusion to your question. If one of the pilots gets sick, the other pilot and the rest of the crew members would just guide the airplane home with rather low risk and they can contact the ground control about it. If all three or four crew members get sick, they can likely receive some instructions from the ground even though there are difficulties. However, even though the autopilot is useful, they will have to land manually and that will be extremely perilous with most old aircraft without proper training.

[1] North Atlantic Communications - History

[2] History of Gander Oceanic/Area Control Centre, J. Pinsent

[3] History of Gander Aeradio, C. Walsh

[4] Bendix PB-20 description

[5] Trident at 60: The first airliner with autoland, D. Carrara

[u/foraminifer → u/Downtown-Act-590]

Thank you so much, what an excellent answer!