This article, while not specifically about the euphemism, details it's origin and use among pilots.

https://captain-al-speaking.com/2018/12/06/flying-west/

Going to the west as euphemism for death is mentioned on the History of Egypt Podcast (that’s Ancient history, if you didn’t guess).

My granddad (WW2 air vet) used to give his father's (WW1 air vet) toast to the whole family every thanksgiving:

Here's to the sands of the hourglass,

a measure of time as it flies;

Here's to the men who flew West today,

Three cheers for the next man who dies!

Read Wolfgang Langewiesche's America from the Air: An Aviator's Story if you want to read some of the best writing about the romance of flying.

I’m assuming this is the father of William?

Correct! Current editions include a foreword written by William.

Wolfgang is much better known for Stick And Rudder, which is about technical aspects of aviation.

If you want romance of flying, and depending on your style of "romance", you might try _Glacier Pilot_ a biography of Bob Reeve who came back from flying in South America as a bush pilot with undiagnosed polio, made it to Alaska, and perfected the art of crash landing on glaciers as a perfectly normal way of doing business. The book was written by Beth Day (Romulo?) who I believe was his granddaughter.

I vaguely remember this from reading Biggles. I think came from pilots getting shot down over enemy lines on the western front in WWI.