What is unaffected when the BLEED AIR inflow switch is turned OFF?

When the BLEED AIR inflow switch is turned OFF, the operation of the On-Board Oxygen Generating System (OBOGS) remains unaffected. OBOGS draws atmospheric air, which it then processes to generate oxygen for the pilot and passenger. Its operation relies on engine bleed air for supplemental oxygen supply but does not depend solely on it.

In this context, when the bleed air is turned off, it does not impact the functioning of the OBOGS because the system can still utilize atmospheric air for its oxygen generation process. This allows the crew to maintain breathable oxygen levels even if engine bleed air is not being utilized.

The other options, such as cabin altitude, fuel flow, and oxygen levels, could be affected when the BLEED AIR inflow switch is turned off. Cabin altitude might change due to the loss of pressure regulation, fuel flow can be influenced by engine performance affected by the loss of bleed air, and oxygen levels could decline without the proper functioning of systems utilizing bleed air. Therefore, the correct choice highlights the resilience of OBOGS in maintaining oxygen supply independently of the BLEED AIR inflow switch status.