Narrative:

Approaching ord from the west southwest; we were told that the ATIS had just changed and to expect localizer 9R. 10C and 9L ILS were the arrival runways we were expecting. Weather about 800-4. We had briefed ILS 10C and retrieved landing data for the short runway; 9L; to get ahead in the event we were assigned 9L.I installed ILS 9R in the FMS noting several localizer only approaches in the database but no localizer only for 9R. After installation; while receiving many vectored turns typical of ord; I briefed the approach using the QRH as a guide. During the route review; we noticed a step down fix; inside the FAF; that was not loaded. I again checked for a localizer only approach in the FMS and after again finding none; I asked the captain to program yonut at or above 1700 in the box. We now had waypoints from devon; just outside the FAF; lanse; through the missed approach procedure programmed with altitudes verified. The brief ended with a disagreement over minimum autopilot disengagement altitude; derived decision altitude (dda) vs. 50ft below dda. An 'old way' versus 'the current way'? I don't know; so I referred to fight manual and we were both now on board with dda as minimum disengagement altitude. Brief done.now on a long; but tight; right down wind at 8000 feet I consider asking the captain to program some of the outer fixes on the localizer course because we're now outside of wasco over 20 miles from the field. I decided to instead brief that the fixes were defined off of the ILS DME and we can use the DME for situational awareness on the step down fix locations once on final. This is one thing that; had we programmed the fixes; would have elliminated our future error.next; we are given 2 turns to final; 'cross wasco at or above 7000; cleared 'the approach'. Appropriately; the captain read back includes the runway assignment and a request for confirmation. I set the intercept heading in heading mode and state that I'm arming navigation for the intercept due to common localizer instability at long range. We are at 8000; on localizer in navigation with the final extended from devon.now the error... I look at the magenta ILS info lower left of pfd to find good ident; proper frequency and no DME. I think to myself 'I thought the ILS DME is supposed to be there'........so....I scan the instruments and find this green number upper right of the nd (navigational display) that looks about right and comfortably decide that all is well........ Yeah; as I sit and write this; I can hardly believe it. But here's the kicker; I made no mention of my thoughts regarding the DME issue and began calling distances to the next waypoint/stepdown off of the nd distance to active waypoint which was either lanse or yonut (I don't recall which was displayed). It should have been lance with the course extended through devon. ([It occurs] that I am reading ILS DME). We are both totally focused on the approach and have both latched onto the distance we read most often. Range to next way point. Not good! This continues with excellent CRM until; while level at 4000; we set 2300 for lance. We are now in localizer capture with flight trk/fpa selected. I state that we are passing 12.3DME (devon) as I pull to begin out of 4000; devon appears at the top of the nd and we both realize we've done something wrong. We reset 4000 in the window; reverse to a climb from 3800 back to 4000; I look straight at the magenta ILS DME that is now working. We never heard a word from ATC.we now have instant sa (situational awareness). We confirm that we had both failed independently in the same way. Reconfirm our sa and focus back on the now to complete the approach and landing without further abnormalities. We then debrief thoroughly at the gate. This is my/our error. I own that. But looking at the approach; ord 9R DME should have been receivable from our base turn and it wasn't. That was step one in the confusion.

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Original NASA ASRS Text

Title: Air carrier flight crew reported difficulty in interpreting displays of the FMS which resulted in an altitude deviation during the approach.

Narrative: Approaching ORD from the West Southwest; we were told that the ATIS had just changed and to expect LOC 9R. 10C and 9L ILS were the arrival runways we were expecting. Weather about 800-4. We had briefed ILS 10C and retrieved landing data for the short runway; 9L; to get ahead in the event we were assigned 9L.I installed ILS 9R in the FMS noting several LOC only approaches in the database but no LOC only for 9R. After installation; while receiving many vectored turns typical of ORD; I briefed the approach using the QRH as a guide. During the route review; we noticed a step down fix; inside the FAF; that was not loaded. I again checked for a LOC only approach in the FMS and after again finding none; I asked the Captain to program YONUT at or above 1700 in the box. We now had waypoints from DEVON; just outside the FAF; LANSE; through the missed approach procedure programmed with altitudes verified. The brief ended with a disagreement over minimum autopilot disengagement altitude; Derived Decision Altitude (DDA) vs. 50ft below DDA. An 'old way' versus 'the current way'? I don't know; so I referred to Fight Manual and we were both now on board with DDA as minimum disengagement altitude. Brief done.Now on a long; but tight; right down wind at 8000 feet I consider asking the Captain to program some of the outer fixes on the LOC course because we're now outside of WASCO over 20 miles from the field. I decided to instead brief that the fixes were defined off of the ILS DME and we can use the DME for situational awareness on the step down fix locations once on final. THIS IS ONE THING THAT; had we programmed the fixes; WOULD HAVE ELLIMINATED OUR FUTURE ERROR.Next; we are given 2 turns to final; 'cross WASCO at or above 7000; cleared 'the approach'. Appropriately; the Captain read back includes the runway assignment and a request for confirmation. I set the intercept heading in heading mode and state that I'm arming NAV for the intercept due to common LOC instability at long range. We are at 8000; on LOC in NAV with the final extended from DEVON.NOW THE ERROR... I look at the magenta ILS info lower left of PFD to find good ident; proper frequency and no DME. I think to myself 'I thought the ILS DME is supposed to be there'........So....I scan the instruments and find this green number upper right of the ND (Navigational Display) that looks about right and comfortably decide that all is well........ Yeah; as I sit and write this; I can hardly believe it. But here's the kicker; I made no mention of my thoughts regarding the DME issue and began calling distances to the next waypoint/stepdown off of the ND distance to active waypoint which was either LANSE or YONUT (I don't recall which was displayed). It should have been LANCE with the course extended through DEVON. ([It occurs] that I am reading ILS DME). We are both totally focused on the approach and have both latched onto the distance we read most often. Range to next way point. NOT GOOD! This continues with excellent CRM until; while level at 4000; we set 2300 for LANCE. We are now in LOC capture with FLT TRK/FPA selected. I state that we are passing 12.3DME (DEVON) as I pull to begin out of 4000; Devon appears at the top of the ND and we both realize we've done something wrong. We reset 4000 in the window; reverse to a climb from 3800 back to 4000; I look straight at the magenta ILS DME that is now working. We never heard a word from ATC.We now have instant SA (situational awareness). We confirm that we had both failed independently in the same way. Reconfirm our SA and focus back on the now to complete the approach and landing without further abnormalities. We then debrief thoroughly at the gate. This is my/our error. I own that. But looking at the approach; ORD 9R DME should have been receivable from our base turn and it wasn't. That was step one in the confusion.

Data retrieved from NASA's ASRS site 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.