109 cant do XXXX anymore.

[IvanK]

Wrt to Oxy systems. Above 30,000feet (in an unpressurised cockpit) even 100% Oxy is not sufficient. Above 30,000feet an Oxy regulator needs to produce an overpressure at 100% Oxy to keep O2 partial pressures in the blood to acceptable/viable levels. I am not sure if WW2 regulators could automatically produce this required overpressure.

In a pressurised cockpit its not an issue until the Cabin Altitude goes over 30,000feet, then the same arises. B29s were of course pressurised.