A G3 OVERSHOT THEIR ASSIGNED ALT WHEN THE AIR DATA COMPUTER FAILS TO RECOGNIZE THE ALT CAPTURE ALT AND DOES NOT LEVEL THE ACFT AT THE ALT ALERTER SETTING OF FL350. AN OPPOSITE DIRECTION MD80 GETS A TCASII TA.

Narrative

GULFSTREAM ACFT WAS PROCEEDING WBOUND DIRECT TO FLYBY INTXN JUST W OF LVS VOR AT FL430 WHEN ZAB CLRED THEM TO DSND TO FL350. THE FO RESET THE ALT ALERT TO 35000 FT AND THE CAPT STARTED THE DSCNT ON AUTOPLT USING VERT SPD MODE AND APPROX 1500-1800 FPM RATE OF DSCNT SET ON THE SPZ-800 FLT DIRECTOR/AUTOPLT CTL. AS THE ACFT PASSED THROUGH FL360 THE FO CALLED OUT 1000 FT TO GO AND THE CAPT SLOWED THE RATE OF DSCNT SLIGHTLY. THE DSCNT PROCEEDED NORMALLY UNTIL APCHING FL350. AT 35100 FT THE FO CALLED OUT THAT THE AUTOPLT WAS NOT CAPTURING THE SELECTED ALT. THE CAPT IMMEDIATELY SELECTED ALT SELECT ON THE FLT GUIDANCE CTL PANEL BUT THE ACFT CONTINUED THROUGH THE ALT. THE AUTOPLT WAS THEN DISCONNECTED BY THE CAPT AND A PULL-UP MANEUVER EXECUTED. THE ACFT STARTED TO LEVEL AND REVERSE DIRECTION AS THE ALTIMETER INDICATED ABOUT 34700 FT AND WAS LEVEL AT 35000 FT APPROX 10 SECONDS LATER. I BELIEVE THE CONTRIBUTING FACTORS TO THIS INCIDENT TO BE THE POSSIBLE MALFUNCTION OF THE FLT DIRECTOR/AUTOPLT ALT HOLD FUNCTION AND THE CREW'S FAILURE TO REALIZE THAT THE AUTOPLT WAS NOT DOING ITS JOB UNTIL TOO LATE. ANOTHER FACTOR WAS THE CAPT HAD JUST COMPLETED 21 DAY INITIAL TRAINING ON AN ACFT WITH A VERY DIFFERENT FLT GUIDANCE CTLR (FMZ-8400). SUBSEQUENT CORRECTIVE ACTIONS: 1) A VISIT TO ZAB WAS MADE THE NEXT DAY BY THE PLT. 2) ALL ACFT SYS INCLUDING THE ADC'S; ALTIMETERS; FLT DIRECTOR COMPUTERS AND AUTOPLT WERE CHKED BY THE AVIONICS SHOP IN ALBUQUERQUE THE NEXT DAY. TWO DISCREPANCIES WERE FOUND: A) THE #1 XPONDER COULD NOT BE SUPPLIED DATA FROM THE #2 ADC; AND B) ON ONE ATTEMPT TO CAPTURE ALT; THE #2 FLT DIRECTOR FAILED. 3) CREW PROCS ARE BEING CHANGED SO THAT IN ADDITION TO THE NORMAL CALLOUT AT 1000 FT ABOVE OR BELOW THE ASSIGNED ALT OR RESTR THE COPLT WILL ALSO STATE 'RATE OF DSCNT 1000 FPM OR LESS AND FLT DIRECTOR ARMED.' 4) THE NEW PROC WILL BE SENT TO FLT SAFETY TO BE INCORPORATED INTO OUR FLC SEMI-ANNUAL TRAINING PROGRAM. 5) A CREW MEETING HAS BEEN SCHEDULED TO INFORM ALL PLTS OF THE NEW PROC AND TO EXPLAIN FURTHER THE LIMITATIONS OF THE AUTOPLT SYS. SUPPLEMENTAL INFO FROM ACN 396174: IMMEDIATELY FOLLOWING THIS AN MD80 AIRLINER AT FL330 RPTED TO ATC THEY WERE RECEIVING A TA ALERT ON TCASII. AT THAT TIME WE WERE QUESTIONED BY ATC AND TOLD TO CALL CTR ON THE GND. FROM THAT POINT ON A NORMAL DSCNT AND LNDG WERE MADE. WE HAVE TWO TYPES OF ACFT WITH TWO DIFFERENT FLT GUIDANCE COMPUTERS. ONE DOES NOT REQUIRE ACTIVATION OF ALT SELECT TO CAPTURE THE PRESELECTED ALT. AFTER FLYING THIS ONE TYPE FOR A NUMBER OF TRIPS AND THEN SWITCHING ACFT; IT DOES TAKE A CONTINUOUS EFFORT TO MAKE SURE ALT SELECT IS SELECTED. RECOMMENDATIONS: THE PNF SHOULD CALL '1000 FT TO GO; ALT SELECT.'