3.7. OBOGS Check. It is critical to check oxygen connections to ensure system integrity from the supply to the mask IAW T.O. 1T-6A-1. Don the oxygen mask and verify that the supply lever is on, and the concentration lever is normal. Check the flow indicator shows flow (white) when inhaling and no flow (black) when exhaling. Place the concentration lever to MAX to ensure the light illuminates and recheck the flow indications. Return the concentration lever to normal. Check the mask seal by selecting EMERGENCY and momentarily holding your breath. A good mask seal is indicated by a no-flow indication on the regulator (black). The mask should be worn for the entirety of the OBOGS BIT test (approximately 3 or 4 minutes IAW T.O. 1T-6A-1 aircraft serial coding) to ensure a proper test is accomplished. If the mask is dropped after the appropriate BIT time, the corresponding OBOGS regulator should be set to the OFF position to prevent a possible OBOGS FAIL situation prior to takeoff.

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