Final answer:
The maximum altitude of a pressurized aircraft without drop down masks is typically limited by aviation regulations to 25,000 feet to prevent low oxygen availability in case of cabin depressurization.
Step-by-step explanation:
The maximum altitude of a pressurized aircraft in commercial operation that lacks drop down masks is determined by aviation regulations. For flights without supplemental oxygen systems, like drop down masks, the Federal Aviation Regulations typically limit the cabin altitude to 25,000 feet. Above this altitude, the availability of oxygen can become critically low, endangering passengers and crew if cabin depressurization occurs. Therefore, regulations require the availability of supplemental oxygen for all occupants after a point, even for unexpected emergencies.