ACR X UNAUTH DSCNT FROM ASSIGNED ALT. PLTDEV.

Narrative

AFTER THE FE OBTAINED THE ATIS FOR US AT DTW; WE DECIDED TO REQUEST A VISUAL APCH TO RWY 27. THE CAPT (PNF) ASKED IF CTR COULD CALL AHEAD WITH OUR REQUEST FOR RWY 27R; RWY 21R WAS THE ACTIVE ON THE ATIS. CTR CALLED US BACK WITH A CLRNC DOWN TO 12000 FT AND SAID DETROIT OK'ED RWY 27R. AS WE APCHED 12000 FT; CTR TOLD US TO CONTACT METRO TWR AND GAVE US THE TWR FREQ. THE CAPT CHKED US IN SAYING WE WERE LEVELING AT 12000 FT WITH THE FIELD IN SIGHT. TWR SAID 'ROGER ACR X; YOU'RE CLRED TO LAND RWY 27R.' I REMARKED TO THE CAPT THAT I GUESS WE'RE CLRED OUT OF 12000 FT FOR THE APCH. HE SAID 'I GUESS SO' AND WE CONTINUED OUR DSCNT INTO DETROIT. APCHING 8000 FT; TWR ASKED US TO CONTACT APCH. I CONTINUED MONITORING TWR; WHILE THE CAPT USED THE OTHER VHF TO CONTACT APCH. APCH GUERIED US IF WE HAD CLRNC FOR AN APCH. THE CAPT RESPONDED THAT TWR HAD CLRED US TO LAND; TO WHICH APCH SAID 'YES; BUT I NEVER GAVE YOU APCH CLRNC.' HE THEN CLRED US TO 3000 FT AND TOLD US TO CALL THE FIELD. THE CAPT CALLED THE FIELD IN SIGHT; WE WERE CLRED THE VISUAL APCH; AND THEN SWITCHED BACK TO TWR. TWR RECONFIRMED OUR LNDG CLRNC. EVEN THOUGH IT IS NOT UNUSUAL FOR US TO EXPERIENCE APCH/TWR/GND CONSOLIDATED INTO ONE DURING THE NIGHT; I REDISCOVERED THE OLD MAXIM OF 'WHEN IN DOUBT; QUERY THE CTLR.' IT DID SEEM UNUSUAL FOR TWR TO CLR US TO LAND WITHOUT GOING THROUGH THE RITUAL OF BEING CLRED 1) OUT OF AN ALT; AND 2) FOR AN APCH. WHILE WE EXPRESSED OUR THOUGHTS IN THE COCKPIT WE NEVER CLARIFIED THINGS WITH ATC. DURING THE QUIET OF NIGHT OPS IT'S EASY TO RELAX YOUR GUARD; BUT I FOUND THE IMPORTANCE OF ALWAYS HEARING THE STANDARD PHRASES AND CLRNCS.