FLT INSTRUCTOR; WITH INST STUDENT; ACCEPTS A LOC DME APCH WHEN THE ACFT WAS NOT EQUIPPED WITH DME. HE SUBSTITUTED GPS EQUIP FOR DISTANCE MEASURING; WHICH WAS APPROVED FOR VFR ONLY.

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WE HAD INITIALLY FILED AN IFR FLT PLAN GOING FROM SMO TO SFO; BUT WERE TOLD OF AN APPROX 2 HR DELAY BY SMO GND. AT THAT POINT WE REQUESTED A NEW CLRNC TO SNS AND WERE GIVEN SAID CLRNC. OUR INITIAL FLT PLAN (TO SFO) HAD BEEN FILED WITH A BRIEFER BY TELEPHONE; AND SPECIFICALLY INDICATED THAT WE WERE A C172/U (NO DME). I AM NOT SURE IF THIS INFO WAS TRANSLATED ONTO OUR NEW IFR FLT PLAN THAT WE GOT ON THE RADIO WITH SMO GND BECAUSE AS WE APCHED SJC (WE HAD CHANGED OUR DEST FROM SNS TO SJC INFLT WITH ATC) WE WERE CLRED FOR A LOC/DME APCH TO SJC. WE DID HAVE GPS ONBOARD TO GIVE US DISTANCE INFO FOR THE APCH; BUT I SUSPECT THIS WAS TECHNICALLY ILLEGAL SINCE THE GPS WAS CERTIFIED FOR 'VFR ONLY' AND WE REALLY HAD NO DME VHF EQUIP ONBOARD. RATHER THAN REQUESTING A DIFFERENT APCH (WHICH TECHNICALLY I SHOULD HAVE DONE) WE CONTINUED IN VFR CONDITIONS; USING THE GPS FOR DISTANCE INFO. THE ENTIRE APCH INSIDE THE KLIDE INTXN WAS IN VFR CONDITIONS; OUR 'STEPDOWNS' GIVEN BY ATC PRIOR TO KLIDE INTXN HAD GOTTEN US OUT OF THE CLOUDS. FROM NOW ON; I'LL MAKE SURE ATC KNOWS OUR EQUIP SIT.