KINGAIR BE200 PLT HAS PRESSURIZATION LOSS; DECLARES AN EMER AND LANDS.

Narrative

AFTER WE HAD STARTED OUR INITIAL DSCNT AND I INCREASED THE RATE OF DSCNT SLIGHTLY; I HEARD A 'THUMP' OR 'SNAP' FOLLOWED BY AN EXTREME SENSATION OF CABIN CLB (MY EARS). IT TOOK ME A SECOND OR TWO TO ASSESS WHAT WAS HAPPENING WHILE THE CABIN MASKS WERE DEPLOYING AND I WAS TRYING TO INTERP THE 'CABIN RATE' NEEDLE; WHICH WAS PEGGED TO THE R (STRANGE LOOKING BECAUSE I HAD FLOWN OTHER PLANES WITH A NORMAL INDICATION TO THE R; SO IT TOOK ME A SECOND; EVEN THOUGH PHYSICALLY I KNEW WHAT WAS HAPPENING. IT WAS ABOUT THIS TIME THAT I STARTED TO FEEL 'FUNNY' AND 'WARM.' IT THEN ALL CAME TO ME ABOUT WHAT EXACTLY WAS GOING ON AND WHAT I HAD TO DO (I GUESS IT WAS AT THIS TIME THAT MY TRAINING TOOK OVER). I THEN IMMEDIATELY TRIED TO DON MY MASK; AND IT WOULDN'T FIT OVER MY HEADSET. I JUST HELD TO MY FACE WITH MY R HAND AND FLEW THE AIRPLANE WITH MY L AND CONTINUED BREATHING WHILE NOTIFYING ATC I NEEDED LOWER (I WAS ALREADY IN A FAST DSCNT); AND THAT WE HAD A PRESSURIZATION FAILURE. I THINK INITIALLY HE CLRED ME TO FL190. I INSISTED LOWER AND HE ASKED IF I WAS DECLARING AN EMER. I REPLIED 'AFFIRMATIVE' AND HE CLRED ME TO (I THINK) 6000 FT. WE DSNDED; RETURNED TO ZZZ SAFELY. UPON NOTIFYING MAINT AND SOME INSPECTING THEY DISCOVERED THAT THE AIR-TO-GND SQUAT SWITCH LINKAGE HAD BEEN REMOVED FROM ITS MOUNT (DISCONNECTED) TO PERFORM SYS TESTING ON THE GND AND HAD FAILED TO RECONNECT IT. I FAILED TO CATCH IT ON MY PREFLT. APPARENTLY IT WAS POSITIONED IN SUCH A WAY AS TO ALLOW THE ACFT TO PRESSURIZE ON TKOF; BUT MUST HAVE MOVED TO THE 'ON-THE-GND POS' WHEN I BEGAN MY DSCNT; AND DUMPED THE CABIN BECAUSE IT THOUGHT WE WERE ON THE GND.