Hello Mr. Goss,
theory of the oxygen failure is new for me.....in Czech and Polish literature is most often mentioned reason for this crash:
- aerobatic figures to impress his girlfriend or
- result of battle fatigue and physical exhaustion
https://fcafa.com/2010/07/24/josef-frantisek/
I would like to say that Josef František perished the day after his birthday - and because he was not "a Saint" - maybe his death is combination of these factors .....pilots in this time fight fast and they live fast .....
Faenor