I am hoping some one can help me with an issue I am having. My pre-flight check list includes activating (pulling the overhead handle out) to charge the oxygen system, which gives me the green bar on our quick donning masks. But what is also does is deploys the passenger overhead masks! There is a second overhead handle you can pull out to manually deploys the masks, which I haven't pulled out. Has anyone ran into this scenario? I don't think it is a bad barometric switch because I do not get an high cabin altitude alert annunciation. Any ideas?

If the valve to manually deploy the passenger masks is leaking, or the cable is out of rig, the masks will deploy when oxygen pressure is applied to the system. Unfamiliar with the specifics of the F90, but the aircraft I am familiar with have two different altitude switches for the cabin warning and deploying the passenger masks.

To find solutions to this King Air F90-1 issue, it would be better if you post in the Beech Turbines Forum.