Narrative:

On intercept vector to final approach, we were cleared 'ILS runway 21L, maintain 5000 ft until robbi and 170 KIAS until pukle.' first officer was PF. I idented his localizer frequency correctly tuned to runway 21L. I continued to monitor the dxo VOR, located on the field at dtw, so I could track distance/azimuth to field. We were VMC, but scattered clouds were between us and the field at approximately 3000 ft AGL. We joined the localizer at 5000 ft, and I checked the DME to insure we were inside robbi and see the next step down altitude of 4000 ft. We began the descent and when we leveled, I noted we were below (1 DOT) GS. This surprised me as I thought we should have been above GS, given our DME. I then doublechked my approach page and noted DME should have been tuned to crl, quite a bit south of dxo. I quickly tuned crl, and we leveled off. However, we did not comply with the controller's instructions to cross robbi at 5000 ft. The controller never mentioned our altitude deviation. Just before handing us to tower, she asked our flight conditions. We replied 'VMC' (we were never IMC) then contacted tower. The remainder of the approach and landing were uneventful. The situation could have been prevented by more careful study of the approach plate. It is unusual to have DME for a localizer approach associated with an off-field VOR. Perhaps a note to this effect should be included on the approach plate. The best solution would be to add DME to the runway 21L localizer. Supplemental information from acn 573179: WX was reported 5500 ft broken, 2300 ft few, visibility 10 mi. I was PF and had the ILS for runway 21L at dtw setup. WX was reported 5500 ft broken, 2300 ft few, visibility 10 mi. I was PF and had the ILS for runway 21L at dtw setup. We were vectored to final by dtw approach to runway 21L. Clearance from approach was maintain 5000 ft till robbi, and 170 KTS till pukle. We were on localizer course, captain idented it, and at 5000 ft GS was alive, but not moving. DME from captain's side showed inside robbi. Field was not in sight due to cloud cover, so I decided to descend to the next minimum altitude. We still could not pick up the field, so I continued to descend to the next minimum, which was 2600 ft, based on the DME we were receiving. At 2600 ft, we picked up the field and realized the DME and GS were not making sense. The VOR frequency was set to dxo, not clear as required on the approach. We maintained visual with the field, intercepted the GS and landed uneventfully. Tower and approach never questioned our altitude. When we switched the VOR to crl, we realized we started descending too early. Lesson learned was always back up what both pilots have set for the approach -- even when you plan on a visual approach.

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Original NASA ASRS Text

Title: B737-300 CREW MISSET THE #1 VOR TO THE WRONG VORTAC TO HAVE VALID DME MILEAGE TO CONFIRM INTXNS ON THE APCH TO RWY 21L AT DTW. THEY HAD AN ALTDEV AS A RESULT.

Narrative: ON INTERCEPT VECTOR TO FINAL APCH, WE WERE CLRED 'ILS RWY 21L, MAINTAIN 5000 FT UNTIL ROBBI AND 170 KIAS UNTIL PUKLE.' FO WAS PF. I IDENTED HIS LOC FREQ CORRECTLY TUNED TO RWY 21L. I CONTINUED TO MONITOR THE DXO VOR, LOCATED ON THE FIELD AT DTW, SO I COULD TRACK DISTANCE/AZIMUTH TO FIELD. WE WERE VMC, BUT SCATTERED CLOUDS WERE BTWN US AND THE FIELD AT APPROX 3000 FT AGL. WE JOINED THE LOC AT 5000 FT, AND I CHKED THE DME TO INSURE WE WERE INSIDE ROBBI AND SEE THE NEXT STEP DOWN ALT OF 4000 FT. WE BEGAN THE DSCNT AND WHEN WE LEVELED, I NOTED WE WERE BELOW (1 DOT) GS. THIS SURPRISED ME AS I THOUGHT WE SHOULD HAVE BEEN ABOVE GS, GIVEN OUR DME. I THEN DOUBLECHKED MY APCH PAGE AND NOTED DME SHOULD HAVE BEEN TUNED TO CRL, QUITE A BIT S OF DXO. I QUICKLY TUNED CRL, AND WE LEVELED OFF. HOWEVER, WE DID NOT COMPLY WITH THE CTLR'S INSTRUCTIONS TO CROSS ROBBI AT 5000 FT. THE CTLR NEVER MENTIONED OUR ALTDEV. JUST BEFORE HANDING US TO TWR, SHE ASKED OUR FLT CONDITIONS. WE REPLIED 'VMC' (WE WERE NEVER IMC) THEN CONTACTED TWR. THE REMAINDER OF THE APCH AND LNDG WERE UNEVENTFUL. THE SIT COULD HAVE BEEN PREVENTED BY MORE CAREFUL STUDY OF THE APCH PLATE. IT IS UNUSUAL TO HAVE DME FOR A LOC APCH ASSOCIATED WITH AN OFF-FIELD VOR. PERHAPS A NOTE TO THIS EFFECT SHOULD BE INCLUDED ON THE APCH PLATE. THE BEST SOLUTION WOULD BE TO ADD DME TO THE RWY 21L LOC. SUPPLEMENTAL INFO FROM ACN 573179: WX WAS RPTED 5500 FT BROKEN, 2300 FT FEW, VISIBILITY 10 MI. I WAS PF AND HAD THE ILS FOR RWY 21L AT DTW SETUP. WX WAS RPTED 5500 FT BROKEN, 2300 FT FEW, VISIBILITY 10 MI. I WAS PF AND HAD THE ILS FOR RWY 21L AT DTW SETUP. WE WERE VECTORED TO FINAL BY DTW APCH TO RWY 21L. CLRNC FROM APCH WAS MAINTAIN 5000 FT TILL ROBBI, AND 170 KTS TILL PUKLE. WE WERE ON LOC COURSE, CAPT IDENTED IT, AND AT 5000 FT GS WAS ALIVE, BUT NOT MOVING. DME FROM CAPT'S SIDE SHOWED INSIDE ROBBI. FIELD WAS NOT IN SIGHT DUE TO CLOUD COVER, SO I DECIDED TO DSND TO THE NEXT MINIMUM ALT. WE STILL COULD NOT PICK UP THE FIELD, SO I CONTINUED TO DSND TO THE NEXT MINIMUM, WHICH WAS 2600 FT, BASED ON THE DME WE WERE RECEIVING. AT 2600 FT, WE PICKED UP THE FIELD AND REALIZED THE DME AND GS WERE NOT MAKING SENSE. THE VOR FREQ WAS SET TO DXO, NOT CLR AS REQUIRED ON THE APCH. WE MAINTAINED VISUAL WITH THE FIELD, INTERCEPTED THE GS AND LANDED UNEVENTFULLY. TWR AND APCH NEVER QUESTIONED OUR ALT. WHEN WE SWITCHED THE VOR TO CRL, WE REALIZED WE STARTED DSNDING TOO EARLY. LESSON LEARNED WAS ALWAYS BACK UP WHAT BOTH PLTS HAVE SET FOR THE APCH -- EVEN WHEN YOU PLAN ON A VISUAL APCH.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.