What do you mean by "heard both in London and New York"? The Titanic was actively sending out distress signals via telegraph as it sank, but those signals weren't strong enough to reach land. They were picked up by other nearby vessels and relayed.
It would have been hard *not* to hear it on both sides of the Atlantic, even with the primitive receivers of the day.
And to answer the question about why we can't use lower frequencies on planes, part of the answer lies in antenna length, which is related to wavelength. Lower frequency = longer wavelength, which in turn means larger antenna (yes, I know this is a very broad generalization, and also not the complete/only reason). Look up the antenna required for 1Mhz.
You wind a loading coil on a plastic dustbin.
?? Is there a different meaning of telegraph than I’m familiar that works without direct connected wires?