AN ACR BRASILIA-120 LTT CAPT INADVERTENTLY DROPPED THE OXYGEN MASKS IN FLT.

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CRUISING AT FL280; OUR CABIN ALT BEGAN TO RISE AT 500 FPM. A DSCNT REQUEST WAS MADE TO ZID. AUTO PRESSURIZATION MALFUNCTION CHKLIST WAS PERFORMED WHICH REQUIRES CHANGING TO MANUAL CTL. WHEN SWITCHING TO MANUAL MODE; THE CAPT GRABBED THE WRONG SWITCH ('MAN' PAX OXYGEN) AND DEPLOYED AUTOMATIC DROP DOWN MASK IN CABIN. PRESSURIZATION OPERATED NORMALLY AT FL240. NOTE THAT THE PRESSURIZATION AND OXYGEN CTL SWITCHES ARE CLOSELY LOCATED AND VISUALLY IDENTICAL; BOTH BEING GUARDED AND LABELED 'MAN' AND 'AUTO.' CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: A BRASILIA 120 CAPT HIT THE WRONG SWITCH AND DROPPED THE OXYGEN MASKS WHEN HE WAS TRYING TO CTL PRESSURIZATION THAT WAS MALFUNCTIONING. HE ADMITS THAT HE IS MAKING EXCUSES FOR HIS BAD SWITCHING PROC WHEN HE STATES THAT THE SWITCHES ARE VERY SIMILAR AND NEARLY SIDE-BY-SIDE (4 INCHES APART). THE REALLY BAD PART OF THIS EXERCISE WAS NONE OF THE PAX PUT ON THEIR OXYGEN MASKS -- THEY ASKED THE FLT ATTENDANT IF THEY WERE NECESSARY. UNFORTUNATELY; THE FLT ATTENDANT CAME TO THE COCKPIT TO SEE IF THERE WAS A PRESSURIZATION EMER RATHER THAN MAKING SURE THAT ALL MASKS WERE PROPERLY PUT ON AND USED.