LR45 FLT CREW; DURING ILS FINAL APCH; WHILE THE ACFT WAS BEING FLOWN ON AUTOPLT; HAS THE ACFT PITCH-UP DEPARTING THE SELECTED ALT.

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WHILE ON A FINAL VECTOR FROM PITTSBURGH APCH TO INTERCEPT THE FINAL APCH COURSE FOR ILS 32; WE WERE GIVEN TURN L TO 300 DEG MAINTAIN 3000; CLRED ILS 32 APCH. AT THAT POINT; I ARMED THE APCH MODE. THE AUTO PLT WAS ENGAGED DURING THE ENTIRE APCH (WHILE BEING VECTORING). AT 7 DME FROM MMJ; THE AIRPLANE; WHILE ON AUTOPLT; PITCHED UP VIOLENTLY AND STARTED AN ATTEMPT TO CLB UP TO THE ALT (FROM OUR POS) TO INTERCEPT THE GLIDESLOPE. ATC GAVE US 3000 FT; BUT THE ACFT; ON AUTOPLT; TRIED TO CATCH OR INTERCEPT THE GLIDESLOPE FROM OUR LOCATION. IN THE PITCH-UP ACTION CAUSED BY THE AUTOPLT; THE ACFT CLBED 200 FT TO 250 FT. AS SOON AS I SAW THE AUTOPLT PITCHING THE ACFT NOSE UP TO MEET THE GLIDESLOPE I DISCONNECTED THE AUTOPLT IMMEDIATELY AND STARTED TO PITCH THE ACFT DOWN TO ASSIGNED ALT OF 3000 FT. THIS ACFT (LR45) HAS HONEYWELL AVIONICS AND THERE IS A KNOWN PROB WITH THE SOFTWARE IN THE PROB. THIS HAS OCCURRED SEVERAL TIMES BEFORE. THE PROB DOES NOT OCCUR EVERY TIME; BUT HAS HAPPENED OFTEN; AND WITH OTHER LR45'S IN OUR FLEET AND OTHERS. THE ACFT WHILE ON AUTOPLT PITCHES UP VERY SUDDENLY AND YOU IMMEDIATELY DISCONNECT IT AND START PUSHING THE NOSE OVER CAUSING NEGATIVE G'S (PAXS CAME OUT OF SEATS) TO RE-ESTABLISH ALT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE ACFT DEPARTED THE SELECTED ALT PROGRAMMED IN THE 'ALT WINDOW' PRIOR TO THE GLIDE SLOPE BECOMING ACTIVE. ADDITIONALLY; THE RPTR ADDED THAT LEAR CORPORATION HAS PUBLISHED A CAUTION THAT THE GLIDE SLOPE MAY BECOME UNUSABLE WHEN THE FLT CREW TRANSMITS ON THE VHF RADIO. ALTHOUGH THIS ANALYST QUESTIONED THE RPTR REGARDING THE LOSS OF GLIDE SLOPE SIGNAL DURING VFR WX AND THE POSSIBILITY THAT THE 'ILS SAFE ZONE' MAY HAVE BEEN PENETRATED; THE RPTR INDICATED THAT THIS PHENOMENON HAS BEEN RPTED BY OTHER FLT CREWS DURING ALL TYPES OF WX; WHEN THE 'ILS SAFE ZONE' WAS IN AFFECT. THE RPTR ALSO STATED THAT THIS ANOMALY ONLY OCCURS DURING SPECIFIC RWY/ILS COMRINATIONS (IE: ILS 32 PIT).