MLG HAS ALTDEV WHEN TUNED TO WRONG VOR.

Narrative

WHILE ON THE EL NIDO 3 ARR INTO SJC (HYP240047) WE WERE GIVEN A HDG FROM BAY APCH OF 270 DEGS TO INTERCEPT THE LOC RWY 30L INTO SJC. ONCE ESTABLISHED ON THE LOC RWY 30L AT 8000 FT THE SUBSEQUENT CLRNC WAS TO 'MAINTAIN 8000 FT UNTIL GILRO/5000 FT UNTIL KLIDE CLRED ILS RWY 30L SJC.' THE NAV #1 WAS ON THE ILS FREQ AND THE NAV #2 WAS ON SJC AT THE TIME. THE CAPT WAS FLYING THE ACFT AND LOOKED AT THE DME ON NAV #2 AND THOUGHT WE WERE INSIDE GILRO AND STARTED DOWN. AT THAT TIME THE FO CHANGED THE NAV #2 TO SAU. WHEN THE SAU DME CAME UP; WE REALIZED WE WERE APPROX 1.5 MI OUTSIDE GILRO AND STOPPED OUR DSCNT AT 7000 FT. THE CTLR THEN QUERIED US AS TO OUR UNDERSTANDING THAT OUR CLRNC WAS TO CROSS GILRO AT 8000 FT. WE APOLOGIZED FOR THE CONFUSION AND TOLD HIM WE WERE LEVEL AT 7000 FT. HE SUBSEQUENTLY CANCELED OUR APCH CLRNC AND CLRED US TO MAINTAIN 7000 FT; WHICH WE DID. THE CTLR THEN POINTED OUT SOME XING TFC BELOW US AT 6000 FT AND WE RESPONDED WE HAD THAT TFC IN SIGHT. WE WERE AGAIN CLRED THE ILS RWY 30L SJC FOR A NORMAL APCH AND LNDG. UPON REFLECTION WE FELT WE HAD BOTH RECEIVERS SET APPROPRIATELY FOR THE INITIAL CLRNC GIVEN. (NAV #1 ILS/NAV #2 SJC). UPON RECEIVING OUR SUBSEQUENT CLRNC TO CROSS GILRO AT 8000 FT KLIDE AT 5000 FT; ETC; WE HAD TO SWITCH THE NAV #2 TO SAU IN ORDER TO IDENT 66.6 DME FOR GILRO. THIS CHANGING OF NAV FREQS LED TO OUR MOMENTARY CONFUSION AS TO OUR POS IN RELATION TO GILRO AND WHICH NAV FREQ WE HAD SET. A POSSIBLE SOLUTION WOULD BE TO INDENT GILRO OFF OF BOTH SAU AND SJC ON THE APCH CHART.