Date: 201710
Local time of day: 0001-0600
Location: ORD.Airport, IL
Flight conditions: IMC
Weather elements / visibility: Rain
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B ORD
ATC / advisory: TRACON C90
Aircraft component: DME
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Human-Machine Interface; Confusion
Second reporter function: Pilot Not Flying; Captain
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Procedure; Human Factors
Primary problem: Human Factors

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.


Second narrative: Last minute change to a short wet runway; LOC 9R [a] non-precision approach. Installed ILS 9R in the FMS noting several LOC only approaches in the database but no LOC only for 9R--Had to manually build LOC only off of the ILS and add waypoint inside FAF since this was not in the aircraft database. On approach had to pull landing performance info for wet short runway. Frequent Changes to Company SOP and infrequently used limits caused increased task saturation while verifying DDA (Derived Decision Altitude) vs DA and Autopilot disconnect limits inside of 20nm as a result of a late runway change to a Non Precision approach; pulling new landing data; noting that we were very at our bingo fuel for our alternate; etc.Sometime around 8000 MSL; I considered programming additional waypoints outside of the outer FAF on the LOC course. I was busy getting updated ATIS and Landing data and crosschecked the step-down altitudes against the distance displayed on my upper right side of my ND (Navigational Display). As I was busy and all looked as expected; I actually thought to myself that I might be being a bit anal and adding additional cluster and distraction to an already highly rushed approach. I independently decided that DME would be sufficient to determine the step-down fixes. (This could have been that critical error that could have led to a significant event; had we simply programmed the additional waypoints; we wouldn't need to be writing our reports now.)SOP prevailed throughout the approach; and I actually found myself feeling quite pleased with how well both pilots were performing in this highly rushed approach. As we got ALT CAP (Altitude Capture); we were setting next altitudes; call outs and checklists were getting done. Weather radar checked and I felt we were getting caught up to be ready for an uneventful landing in Chicago.While level at 4000; we preset 2300 for LANCE. (We are now in LOC capture with FLT TRK/FPA selected as we observe 0.3 DME) a 3 degree descent is initiated and I scan the ND waypoints. NO! The FAF is way ahead of us; 'Stop the descent and climb immediately to 4;000 FT!' I rescan and realize that we've been referencing the wrong digital display for our distance on the ND. As I am taking this in the actual ILS DME appears on our display. We were about 5 miles outside of the FAF.I shudder to think what could have happened if we had continued our descent. We are fortunate that all of our errors occurred above the published MSA of 3;400 FT. For what it's worth; we never heard a word from ATC. We both reassess and verify our current location on the approach. Confident that we have accurate position info we decide to continue the approach. We then debrief thoroughly at the gate and again at our hotel.


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