B747 DSNDS 7 MI EARLY ON APCH TO RWY 6L AT ANC; AK. PLT FATIGUE AND NON STANDARD ACFT EQUIP ARE THE ISSUES.

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MOST OF THE ACFT OPERATED BY MY EMPLOYER HAVE 2 VOR/DME/ILS RECEIVERS. THIS PARTICULAR ACFT IS DIFFERENT IN THAT IT HAS 2 VOR/DME RECEIVERS AND SEPARATE ILS RECEIVERS WITH NO DME. THEREFORE; WHEN FLYING A LOC OR ILS APCH WITH DME; THE VOR SETS MUST BE TUNED TO THE APPROPRIATE DME CHANNEL SEPARATELY FROM TUNING THE ILS RECEIVERS. WE WERE CLRED FOR THE LOC APCH TO RWY 6L AT ANC. WE PLANNED TO USE DME TO DEFINE THE FAF -- GRACE. HOWEVER; WE FAILED TO TUNE THE CORRECT DME CHANNEL (111.3) AND FLEW THE APCH USING THE VOR DME (114.3). CONSEQUENTLY WE DSNDED APPROX 7 DME EARLY. TWR NOTIFIED US OF A LOW ALT ALERT AS WE APCHED MDA. WE CLBED BACK TO 1600 FT WHILE TUNING THE CORRECT DME CHANNEL. WE FLEW THE APCH CORRECTLY FROM APPROX 2 MI OUTSIDE THE FAF. OFFICIAL WX AT XA53Z WAS WIND 040 DEGS AT 3 KTS; VISIBILITY 1 1/2 MI LIGHT SNOW; MIST; FEW CLOUDS AT 300 FT; BROKEN AT 1200 FT; OVCST 3100 FT; TEMP -8/-9 DEGS; ALTIMETER 30.15. DURING OUR PREMATURE DSCNT WE NEVER HAD VISUAL CONTACT WITH THE SURFACE AT OUR ALT OF APPROX 500 FT MSL. FATIGUE WAS A FACTOR INASMUCH AS WE HAD CROSSED 11 TIME ZONES IN 3 DAYS WITH CONSEQUENT DISRUPTION OF OUR CIRCADIAN RHYTHM. ALL 3 OF US WERE UNABLE TO GET THE REST WE NEEDED IN THE 8 HRS PRIOR TO OUR WAKE-UP DUE TO THIS DISRUPTION. WE WERE VERY FORTUNATE THAT THE TERRAIN IS FLAT IN THE AREA WHERE WE MADE OUR PREMATURE DSCNT.