Narrative:

I was PF, first officer on the third leg of a 4 leg, 1 day trip. This leg was from cwa, wi, back to ord. We had been vectored onto the ILS runway 14R localizer course about 40 mi northwest of ord at 9000 ft. I was using the autoplt to fly the plane, but on my EFIS pfd and navigation displays, was not yet receiving a GS on the ILS DME (we were still too far out to receive those). We were next issued clrncs as follows, maintain 210 KTS/descend to 7000 ft/maintain 7000 ft to bifle (21.1 NM out on ILS DME), slow to 180 KTS, 180 KTS to roamy (OM), cleared ILS runway 14R approach. The autoplt we have on the ATP is very workload intensive, so I was busy starting the descent and messing with power to maintain the speed assignments. The captain had 'given' me the radios while he attended to writing ATIS and our required company in- range calls. Since I was still not receiving DME or GS information, I thought we were already well inside bifle by the time we received our approach clearance. I therefore set the aircraft up in a high rate descent up and to capture the GS from above. I allowed the aircraft to continue through 7000 ft, on the descent -- searching for the GS. I figured as we got closer, I would pick it up and capture it. Passing 6000 ft, the captain 'returned' from his radio work, and queried me for our latest ATC instructions. He also noticed 7000 ft still set in our altitude 'window' of our avionics. I told him our latest clearance and he told me we weren't inside bifle yet and we were well below assigned altitude. I responded that I thought we were cleared the approach and above the GS. What I hadn't noticed also was the captain was receiving a GS and was using the ord DME until we got closer. I leveled the plane at 5700 ft, until we could inform ATC and receive an adjusted clearance. The captain asked ATC if we could get lower, they gave it to us immediately and also cleared us immediately for a visual runway 14L. This seemed to resolve any problems our altitude deviation would have caused, and ATC made no further comments. We did not compromise separation between us and any other aircraft as far as I could tell, as we are equipped with TCASII and it didn't show anyone close on the 12 mi range. Contributing factors to my altitude deviation were not receiving the GS and not receiving DME. Also, I failed to ensure a xchk and obtain adequate navigational reception to xchk our position on the approach, before descending further on our approach clearance. I failed to ensure we were at bifle before descending from 7000 ft. To help ensure I don't repeat this mistake in the future, I have learned a few things and revised my own procedures during approachs. The captain showed me one avionics trick I didn't know about. In this plane, if you're receiving a localizer, but no GS, often if you cycle the receiver, the GS will now come in ok. Also I've vowed to always ensure I double-check our position on the approach with respect to fixes, and ensure adequate navigation reception, before leaving an assigned altitude to continue the approach.

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Original NASA ASRS Text

Title: FLC OF BAE-ATP DO NOT MAINTAIN ALT ON ILS APCH. THEY DSND BEFORE GS INTERCEPT.

Narrative: I WAS PF, FO ON THE THIRD LEG OF A 4 LEG, 1 DAY TRIP. THIS LEG WAS FROM CWA, WI, BACK TO ORD. WE HAD BEEN VECTORED ONTO THE ILS RWY 14R LOC COURSE ABOUT 40 MI NW OF ORD AT 9000 FT. I WAS USING THE AUTOPLT TO FLY THE PLANE, BUT ON MY EFIS PFD AND NAV DISPLAYS, WAS NOT YET RECEIVING A GS ON THE ILS DME (WE WERE STILL TOO FAR OUT TO RECEIVE THOSE). WE WERE NEXT ISSUED CLRNCS AS FOLLOWS, MAINTAIN 210 KTS/DSND TO 7000 FT/MAINTAIN 7000 FT TO BIFLE (21.1 NM OUT ON ILS DME), SLOW TO 180 KTS, 180 KTS TO ROAMY (OM), CLRED ILS RWY 14R APCH. THE AUTOPLT WE HAVE ON THE ATP IS VERY WORKLOAD INTENSIVE, SO I WAS BUSY STARTING THE DSCNT AND MESSING WITH PWR TO MAINTAIN THE SPD ASSIGNMENTS. THE CAPT HAD 'GIVEN' ME THE RADIOS WHILE HE ATTENDED TO WRITING ATIS AND OUR REQUIRED COMPANY IN- RANGE CALLS. SINCE I WAS STILL NOT RECEIVING DME OR GS INFO, I THOUGHT WE WERE ALREADY WELL INSIDE BIFLE BY THE TIME WE RECEIVED OUR APCH CLRNC. I THEREFORE SET THE ACFT UP IN A HIGH RATE DSCNT UP AND TO CAPTURE THE GS FROM ABOVE. I ALLOWED THE ACFT TO CONTINUE THROUGH 7000 FT, ON THE DSCNT -- SEARCHING FOR THE GS. I FIGURED AS WE GOT CLOSER, I WOULD PICK IT UP AND CAPTURE IT. PASSING 6000 FT, THE CAPT 'RETURNED' FROM HIS RADIO WORK, AND QUERIED ME FOR OUR LATEST ATC INSTRUCTIONS. HE ALSO NOTICED 7000 FT STILL SET IN OUR ALT 'WINDOW' OF OUR AVIONICS. I TOLD HIM OUR LATEST CLRNC AND HE TOLD ME WE WEREN'T INSIDE BIFLE YET AND WE WERE WELL BELOW ASSIGNED ALT. I RESPONDED THAT I THOUGHT WE WERE CLRED THE APCH AND ABOVE THE GS. WHAT I HADN'T NOTICED ALSO WAS THE CAPT WAS RECEIVING A GS AND WAS USING THE ORD DME UNTIL WE GOT CLOSER. I LEVELED THE PLANE AT 5700 FT, UNTIL WE COULD INFORM ATC AND RECEIVE AN ADJUSTED CLRNC. THE CAPT ASKED ATC IF WE COULD GET LOWER, THEY GAVE IT TO US IMMEDIATELY AND ALSO CLRED US IMMEDIATELY FOR A VISUAL RWY 14L. THIS SEEMED TO RESOLVE ANY PROBS OUR ALTDEV WOULD HAVE CAUSED, AND ATC MADE NO FURTHER COMMENTS. WE DID NOT COMPROMISE SEPARATION BTWN US AND ANY OTHER ACFT AS FAR AS I COULD TELL, AS WE ARE EQUIPPED WITH TCASII AND IT DIDN'T SHOW ANYONE CLOSE ON THE 12 MI RANGE. CONTRIBUTING FACTORS TO MY ALTDEV WERE NOT RECEIVING THE GS AND NOT RECEIVING DME. ALSO, I FAILED TO ENSURE A XCHK AND OBTAIN ADEQUATE NAVIGATIONAL RECEPTION TO XCHK OUR POS ON THE APCH, BEFORE DSNDING FURTHER ON OUR APCH CLRNC. I FAILED TO ENSURE WE WERE AT BIFLE BEFORE DSNDING FROM 7000 FT. TO HELP ENSURE I DON'T REPEAT THIS MISTAKE IN THE FUTURE, I HAVE LEARNED A FEW THINGS AND REVISED MY OWN PROCS DURING APCHS. THE CAPT SHOWED ME ONE AVIONICS TRICK I DIDN'T KNOW ABOUT. IN THIS PLANE, IF YOU'RE RECEIVING A LOC, BUT NO GS, OFTEN IF YOU CYCLE THE RECEIVER, THE GS WILL NOW COME IN OK. ALSO I'VE VOWED TO ALWAYS ENSURE I DOUBLE-CHK OUR POS ON THE APCH WITH RESPECT TO FIXES, AND ENSURE ADEQUATE NAV RECEPTION, BEFORE LEAVING AN ASSIGNED ALT TO CONTINUE THE 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.