What happens to the oxygen supply on a B747 as the cabin altitude decreases?

As the cabin altitude decreases on a Boeing 747, the pressure in the cabin increases, which directly affects the availability of oxygen. The cabin pressure is maintained at a level that simulates a lower altitude, allowing passengers to breathe normally without supplemental oxygen. As the altitude decreases, the need for supplemental oxygen diminishes because the air pressure and consequently the oxygen availability in the cabin improve.

This results in a decrease in oxygen flow. When the cabin altitude is maintained at a higher level, oxygen flow would be higher to compensate for lower ambient pressure. Therefore, as the cabin altitude decreases, oxygen flow decreases, aligning with the conditions where normal breathing is sufficient for passengers and crew. The other options do not accurately capture this relationship; they imply either an increase in oxygen flow or a change that does not align with the basic principles of cabin pressure management in an aircraft.