Narrative:

The captain was flying the ILS approach to runway 35L den. The controller gave us a heading of 320 degrees to intercept the runway 35L localizer and to descend to 8000 ft. We proceeded with this clearance and then received a further clearance to 'maintain 8000 ft until established, cleared for the ILS runway 35L approach.' our intercept of the localizer put us between chola international (16.6 DME) and dymon international (6.8 DME), with an approach altitude of 9000 ft (7000 ft when authority/authorized by ATC) for the ILS. The GS OTS approach, on the profile view, gives a sector approach altitude of 7000 ft. After receiving the ILS clearance, and as we approached the final approach course, I went to the HSI to monitor the localizer alive. As I did this, I noted our descent through 8500 ft for 8000 ft. The localizer came alive and captured, which I called out and monitored. When this was done, I looked up to see the aircraft was descending through 7600 ft for 7000 ft at approximately 1800 FPM. The captain, without informing me or confirming the sector altitude was correct had put in a new altitude of 7000 ft as we established inbound. He misread the approach plate and put in the sector altitude for the localizer/GS OTS approach, not the ILS, which was the approach we had been cleared for. The correct sector altitude to maintain until GS intercept was 8000 ft, which was the altitude authority/authorized by the ATC approach controller. At 7000 ft and GS intercept, the approach controller asked if we had the airport visually when we came out of 8000 ft. We answered 'affirmative' and continued the approach without further incident. The captain should have briefed that he would follow step down fixes when cleared for the approach. He also should have briefed the appropriate sector altitudes between those fixes. When he changed the altitude in the MCP, he should have informed me, and had me confirm the altitude was correct. Had he done this, we would not have busted our altitude by 1000 ft.

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Original NASA ASRS Text

Title: B737 CREW HAD AN ALT OVERSHOT ON APCH TO RWY 35L AT DEN.

Narrative: THE CAPT WAS FLYING THE ILS APCH TO RWY 35L DEN. THE CTLR GAVE US A HDG OF 320 DEGS TO INTERCEPT THE RWY 35L LOC AND TO DSND TO 8000 FT. WE PROCEEDED WITH THIS CLRNC AND THEN RECEIVED A FURTHER CLRNC TO 'MAINTAIN 8000 FT UNTIL ESTABLISHED, CLRED FOR THE ILS RWY 35L APCH.' OUR INTERCEPT OF THE LOC PUT US BTWN CHOLA INTL (16.6 DME) AND DYMON INTL (6.8 DME), WITH AN APCH ALT OF 9000 FT (7000 FT WHEN AUTH BY ATC) FOR THE ILS. THE GS OTS APCH, ON THE PROFILE VIEW, GIVES A SECTOR APCH ALT OF 7000 FT. AFTER RECEIVING THE ILS CLRNC, AND AS WE APCHED THE FINAL APCH COURSE, I WENT TO THE HSI TO MONITOR THE LOC ALIVE. AS I DID THIS, I NOTED OUR DSCNT THROUGH 8500 FT FOR 8000 FT. THE LOC CAME ALIVE AND CAPTURED, WHICH I CALLED OUT AND MONITORED. WHEN THIS WAS DONE, I LOOKED UP TO SEE THE ACFT WAS DSNDING THROUGH 7600 FT FOR 7000 FT AT APPROX 1800 FPM. THE CAPT, WITHOUT INFORMING ME OR CONFIRMING THE SECTOR ALT WAS CORRECT HAD PUT IN A NEW ALT OF 7000 FT AS WE ESTABLISHED INBOUND. HE MISREAD THE APCH PLATE AND PUT IN THE SECTOR ALT FOR THE LOC/GS OTS APCH, NOT THE ILS, WHICH WAS THE APCH WE HAD BEEN CLRED FOR. THE CORRECT SECTOR ALT TO MAINTAIN UNTIL GS INTERCEPT WAS 8000 FT, WHICH WAS THE ALT AUTH BY THE ATC APCH CTLR. AT 7000 FT AND GS INTERCEPT, THE APCH CTLR ASKED IF WE HAD THE ARPT VISUALLY WHEN WE CAME OUT OF 8000 FT. WE ANSWERED 'AFFIRMATIVE' AND CONTINUED THE APCH WITHOUT FURTHER INCIDENT. THE CAPT SHOULD HAVE BRIEFED THAT HE WOULD FOLLOW STEP DOWN FIXES WHEN CLRED FOR THE APCH. HE ALSO SHOULD HAVE BRIEFED THE APPROPRIATE SECTOR ALTS BTWN THOSE FIXES. WHEN HE CHANGED THE ALT IN THE MCP, HE SHOULD HAVE INFORMED ME, AND HAD ME CONFIRM THE ALT WAS CORRECT. HAD HE DONE THIS, WE WOULD NOT HAVE BUSTED OUR ALT BY 1000 FT.

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.