THE COML PLT WAS RCVG MULT-ENG DUAL INSTRN IN A BEECH 95. AFTER TKOF, THE AIRCREW BEGAN PRACTICING INST APCHS. AFTER MAKING AN ILS RWY 10 APCH TO ENTER LEFT TRAFFIC FOR RWY 28, THE FLT WAS CLRD ONTO A SOUTH DOWNWIND TO BE SEQUENCED TO FOLLOW A PSA BAE-146. WHEN THE BEECH 95 CREW RPRTD THE BAE-146 WAS IN SIGHT, THEY WERE CLRD TO FOLLOW IT. A WITNESS, WHO WAS WATCHING THE BAE-146 LAND, STATED THAT WHEN HIS ATTENTION WAS FOCUSED ON THE PLANE (BEECH 95) SOME DISTANCE BEHIND THE COMMERCIAL PLANE (BAE-146), IT WAS IN A STEEP NOSE DOWN DSCNT TOWARD THE GND & IN A RGT SPIN. THE BEECH 95 CRASHED IN APRX A 125 DEG NOSE DOWN ATTITUDE. NO PREIMPACT PART FAILURE OR MALFUNCTION WAS FOUND. HOWEVER, THE ACFT WAS FND CONFIGURED FOR A PSBL SIMULATED ENG-OUT APCH; I.E., THE RUDDER TRIM TAB & INDICATOR WERE FND WITH ABT 20 TO 22 DEG DEFLECTION, THE LEFT & RGT TACH INDICATED 1900 & 2700 RPM, RESPECTIVELY, & THE FLAP & FLAP ACTUATORS WERE FND IN A RETRACTED PSN. THE IN-FLT SEPN BTW THE BEECH 95 & BAE-146 WAS NOT DETERMINED. TWR PSNL DIDN'T PROVIDE A WAKE TURBC ADZY.