WHEN A SAAB; SF340; WAS BOARDED BY MAINT PERSONNEL AFTER PARKING TO OPEN A STUCK AFT BAGGAGE COMPARTMENT; THE ACFT FELL DOWN ON ITS TAIL CONE. THE TAIL STAND HAD NOT BEEN PUT IN PLACE AND THE BAGGAGE LOAD WAS FOUND TO EXCEED THE CARGO COMPARTMENT WT LIMITATION. SINCE THE ACTUAL WT WAS MORE THAN THE FLC HAD USED IN COMPUTING THE WT AND BAL; THE ACFT CTR OF GRAVITY LIMITS HAD BEEN EXCEEDED DURING THE PREVIOUS FLT.

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AFTER RECEIVING OUR LOAD NUMBERS FROM BOS OPS; THE FO COMPLETED THE WT AND BAL MANIFEST. THE CTR OF GRAVITY CALCULATOR INDICATED THAT THE CTR OF GRAVITY WAS AT THE AFT LIMIT. THE BOS STATION IS NOTORIOUS FOR OVERWT BAGS AND IMPROPER LOADING OF THE ACFT. SINCE THE RAMP NEVER INFORMED US OF A TAILSTAND STUCK CONDITION; WE HAD NO REASON TO OFFLOAD PAYLOAD. (WE LATER FOUND OUT THAT THEY HAD TO REALLY KICK AT THE TAILSTAND TO FREE IT.) SENSING THAT ACFT HAD AN UNUSUAL AFT CTR OF GRAVITY CONDITION; I ELECTED TO HAVE ONE OF OUR COMMUTING FLT ATTENDANTS OCCUPY THE COCKPIT JUMP SEAT AS A SAFETY MEASURE AND TO MOVE THE CTR OF GRAVITY A BIT MORE FORWARD FROM THE AFT LIMIT. USING AN ADMISSION TO THE COCKPIT SECTION OF OUR FLT MANUAL FOR UNUSUAL OR EMER SITS; I JUSTIFIED PLACING THE FLT ATTENDANT IN THE JUMPSEAT. I CONSIDERED THIS AFT CTR OF GRAVITY AS UNUSUAL SINCE IT HAD ONLY BEEN THE THIRD TIME IT HAS OCCURRED TO ME ON THIS ACFT TYPE. (I WAS LATER INFORMED THAT THIS MAY BE A POSSIBLE FAR VIOLATION DESPITE OUR FLT MANUAL BEING POORLY WRITTEN.) THE FLT WAS UNEVENTFUL; WITH NO CTLABILITY PROBS. UPON ARRIVING AT THE RAMP IN JFK; WE WERE ADVISED THAT THE CARGO DOOR WAS JAMMED. THE RAMP HAD NOTIFIED MAINT; THEY WERE WAITING AT THE BOTTOM OF STEPS AS THE ACFT WAS DEPLANED. NORMAL PROC WITH A STUCK CARGO DOOR IS TO USE AN AUX TAILSTAND. THIS WAS NOT DONE. AFTER ALL THE PAX WERE OFF THE AIRPLANE; MYSELF AND THE FO; MAINT WENT AFT THROUGH THE CABIN TO ACCESS THE CARGO COMPARTMENT VIA THE BLOW OUT DOOR. AT WHICH TIME THE ACFT SLAMMED DOWN ON ITS TAIL. BECAUSE OF THE INCIDENT; ALL THE BAGS WERE WEIGHED AND EACH FOUND TO BE ABOUT 20 LBS OVER OUR ESTIMATED BAG WTS. FURTHERMORE; THE ACTUAL WT IN THE AFT CARGO COMPARTMENT WAS 583 LBS OVER ITS LIMIT. THE CTR OF GRAVITY; USING THE ACTUAL WTS; WAS WELL AFT OF THE AFT LIMIT. THE ESTIMATED BAG WT PROGRAM SHOULD BE ABOLISHED AND ONLY ACTUAL WTS SHOULD BE USED WHEN LOADING THIS ACFT.