"Allen" wrote

Learjets do indeed use bottled oxygen and it is found in the nose bay
area. There is a thin capillary that runs into the cockpit to a pressure
gauge. The pressure gauge displays the pressure in the tank regardless of
whether the valve is turned on or off. The pressure in the tank can read
full on the ground but at low temperature at altitude will read several
hundred pounds less.

They do? For primary breathing air at altitude? Is there no cabin air
pressurization provided by bleed air from the engines?

I'm not doubting your word, just trying to understand. I thought all
bizjets used bleed air to pressurize the cabins.
--
Jim in NC