LEAR 35 ACFT AFTER MISSED APCH WAS IN HOLDING PATTERN AND; EITHER FLC DEVIATED ALTS OR THE XPONDER WAS RPTING ERRONEOUS ALTS RESULTING IN LESS THAN LEGAL SEPARATION WITH ANOTHER ACFT IN HOLDING 1000 FT ABOVE. AFTER LNDG; RPTR CAPT WAS ADVISED TO CONTACT THE CTR WHO TOLD HIM ABOUT THE DEVS.

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AFTER A MISSED VOR RWY 33 APCH TO SAF; HOLD AND SECOND APCH; I WAS ADVISED TO CONTACT ZAB FOR A POSSIBLE ALTDEV UPON LNDG IN SAF. DURING TELEPHONE CONVERSATION WITH ZAB THEY ADVISED MY ALT SHOWED 8800 FT; 9100 FT; 9500 FT; 9200 FT; 9100 FT (APPROX 8 SECONDS BTWN READOUTS). I TOLD ZAB THAT MYSELF AND COPLT NEVER SAW AN ALT IN EXCESS OF 9000 FT. AUTOPLT WAS ENGAGED AND ALT HOLD USED DURING HOLD AT VOR. AT NO TIME DURING APCH WAS I ADVISED OF EXCESSIVE ALT OR THAT A GULFSTREAM WAS IN THE SAME HOLD AT 10000 FT. FAR 91.411 WAS COMPLIED WITH MAR/XX/92 WITH NO DEFECTS NOTED. I WILL QUERY ATC DURING NEXT FEW FLTS TO SEE IF ANY DISCREPANCIES EXIST. IF SO; SYS WILL BE TAKEN IN FOR MAINT IMMEDIATELY. IF NOT; SYS WILL BE RECHKED DURING JUN/97 MAINT. CONDITIONS DURING APCH WERE LIGHT TURB; IMC; RAIN; SNOW AND ICING. AFTER MISSED APCH WAS ANNOUNCED BY MY ACFT; SAF TWR CALLED SAF BELOW MINIMUMS. UPON MISSED APCH ZAB OFFERED US 9000 FT INSTEAD OF PUBLISHED 8200 FT. I ACKNOWLEDGED WE WOULD HOLD AT 9000 FT; FEELING THIS WOULD PROVIDE ZAB WITH BETTER RADAR COVERAGE DUE TO MOUNTAINOUS TERRAIN IN THAT AREA. I AM STILL NOT CERTAIN AS TO WHAT CAUSED THIS PROB. COCKPIT INDICATIONS WERE SHOWING ON ALT; AUTOPLT ENGAGED AND NO ALT ALERT WARNING. I WILL SAY IF ZAB HEARD OR SAW THIS THREAT; AN IMMEDIATE ADVISORY WOULD HAVE BEEN NICE. ALSO; IF I WAS INFORMED ANOTHER ACFT WAS IN THE SAME HOLD I WOULD HAVE STAYED AT 8200 FT FOR THE EXTRA MARGIN. THE FOLLOWING DAY I EXPERIENCED AN AUTOPLT MALFUNCTION ON MY FLT TO ASE. I AM AWAITING A LOANER AUTOPLT COMPUTER. IT HAS BEEN AN INTERMITTENT PROB WHICH I HOPE TO CONFIRM.