AFTER THE ACFT LANDED AT KELLY AFB, TX, ON 10/2/86, THERE WAS A CREW CHG BFR IT DEPD ON THE NEXT FLT. DRG THE NEXT TAKE-OFF, THE ACFT LIFTED OFF NEAR THE MIDPOINT OF RWY 15 (APRX 5775' FM THE APCH END). WHEN IT WAS AT APRX 100' TO 200' AGL,WITNESSES SAW IT GO INTO AN EXTREMELY NOSE HI ATTITUDE & CLIMB ABOUT ANOTHER 500'. ALSO, THE ACFT ROLLED TO THE LEFT & CONTD ROLLING & TURNING LEFT UNTIL IT CRASHED ON THE RAMP IN A NEAR INVERTED ATTITUDE ON A HDG OF ABOUT 070 DEG. THERE WAS EVIDENCE THAT AN ELEVATOR CONTROL (CTL) BLOCK HAD JAMMED THE 1ST OFFICER'S (FO'S) CTL COLUMN WHEN THE ACFT TOOK OFF.THE FO OF THE PREVIOUS FLT HAD INSTALLED IT ON THE CTL COLUMN AFTER THAT FLT. THE FO OF THE ACDNT FLT HAD BEEN HIRED 6 DAYS EARLIER & MAY NOT HAVE BEEN FAMILIAR WITH THE DEVICE. THE BLOCK WAS DESIGNED TO KEEP THE ELEVATOR IN A FAIRED OR SLIGHTLY RAISED (TRAILING EDGE UP) POSITION FOR LOADING OPNS, BUT IT WAS NOT AN APPROVED DEVICE. THERE WAS AN UNWRITTEN PRACTICE FOR THE FO TO INSTALL & REMOVE THE DEVICE.