C150 HAS FAULTY ALTIMETER. ON IFR FLT TRAINING.

Narrative

I HAD A NEW ALTIMETER INSTALLED IN MY C150. I FLEW AN IFR TRAINING FLT AND WAS HAVING TROUBLE HOLDING ALT. AT ONE POINT ATC RPTED A 150-200 FT DISCREPANCY IN ALT. ON THE GND I CAME TO THE CONCLUSION THAT I HAD BEEN OFF IN MY ALT SETTING. I FLEW AGAIN AND WAS IN CONTACT WITH ZOA CLBING; THEN WAS HANDED OVER TO SUU AND SUBSEQUENTLY SAC; WHEN I WENT TO ADJUST THE ALT SET THAT SUU GAVE ME. I SAW IT WAS READING HG 28 INGHES HG. I WAS BUSY UNDER THE HOOD AND THOUGHT I HAD INADVERTENTLY TURNED THE KNOB TOO FAR. MY INSTRUCTOR PUT IN THE RIGHT SETTING. WHEN I BEGAN MY APCH TO SAC THE CTLR QUERIED OUR ALT. IT TURNED OUT THE ALTIMETER WAS READING 1400 FT HIGHER THAN WE WERE! WE BROKE OFF THE APCH AND HEADED FOR HOME BASE IN CAVU CONDITIONS. WHILE TALKING TO SUU ON THE RETURN IT TURNED OUT THAT THEIR ALT READING EQUIP WAS INOP WHICH IS WHY OUR ALT DISCREPANCY HAD NOT BEEN PICKED UP EARLIER. FORTUNATELY WE WERE IN VFR CONDITIONS THAT PARTICULAR DAY. IF I HAD BEEN IFR WITH A FAILED ALTIMETER AND RADAR INOP NEAR THE NAPA HILLS I COULD HAVE ENDED UP JUST ANOTHER PLT ERROR STATISTIC. I HAD A HAND HELD GPS BUT THE ALT READOUT IS UNRELIABLE. WHAT CONCERNS ME IS THE GENERAL LACK OF CONCERN BY THE AVIONICS PEOPLE THAT A BRAND NEW INST FAILED SO DRAMATICALLY. MORAL: DON'T TRUST EVEN A BRAND NEW INST. I WILL ALSO PAY CLOSER ATTN TO MAKE SURE THAT ALTIMETER SETTINGS/ALTIMETER READOUT MATCH CLOSELY AND NOT ASSUME THE ERROR IS MINE AND MONITOR THROUGHOUT FLT. P.S. AS I WAS DOING QUITE A BIT OF MANEUVERING IT DIDN'T BECOME OBVIOUS VISUALLY THAT THE ALT WAS SO FAR OFF UNTIL WE STARTED OUR DSCNT.