Narrative:

Flight was uneventful from takeoff to beginning of descent. It was the captain's leg and he briefed a visual approach to rwy 28C backed up by the ILS. This was what we were expecting based on weather and direction of flight. I believe we were on the BENKY4 RNAV arrival into ord. Somewhere around our turn to downwind (maybe around 'petah'); ATC told us to expect rwy 27L. The captain briefed the backup information and I input the change into the FMS. I remember the captain saying 'I think I read in the NOTAMS that the glideslope is out of service (OTS) for that runway'. This was confirmed when we heard approach tell another aircraft on 27L that it was OTS. Everything from this point on was uneventful until established on final other than specific speeds ATC was instructing us to fly. The swap to tower went something like '[flight number] contact tower on 120.75; maintain 170 KIAS until taffs; contact tower at taffs' (at this point we were about 5 miles from taffs). I'm not sure what all happened to lead to the event around taffs because I was heads down finishing [a] checklist and a lot was happening (contacting tower; slowing to approach speed; finishing the checklist; etc). My assumption is that the captain just put in too much of a descent rate with the ap (autopilot) at what would have been a normal glideslope intercept point. Tower contacted us and said 'low altitude alert check your altitude immediately' I looked up and saw 4 red lights on the PAPI. At this point the captain clicked off the ap and manually re-intercepted a proper visual glideslope. We were stable and checklist complete before 1000 and the landing was uneventful.several factors contributed to this event. Late change of runway; glideslope being out of service; crunch point around taffs intersection compounded by ATC's request of speeds and radio communication; misapplication of ap descent rate at FAF; lack of crosscheck by the crew for adherence to recommended altitudes on the approach plate for 'localizer (GS out)'. Biggest thing would have been to brief the planned descent rate used by the ap based on the glideslope being out. Briefing and delegating adherence to the recommended altitudes for a localizer (GS out) approach. Anticipation of the crunch point around normal glideslope intercept and possibly an early slow/configuration to be stable at the point prior to intercepting a 3 deg glide path. Ap usage and calculated descent rates for localizer approach. Cross-checking and communication by the first officer for deviations based on those recommended altitudes.

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Original NASA ASRS Text

Title: Air carrier First Officer reported ORD Tower issued a low altitude alert to them when they got low on a localizer only approach to Runway 27L.

Narrative: Flight was uneventful from takeoff to beginning of descent. It was the Captain's leg and he briefed a visual approach to Rwy 28C backed up by the ILS. This was what we were expecting based on Weather and direction of flight. I believe we were on the BENKY4 RNAV arrival into ORD. Somewhere around our turn to downwind (maybe around 'PETAH'); ATC told us to expect Rwy 27L. The Captain briefed the backup information and I input the change into the FMS. I remember the Captain saying 'I think I read in the NOTAMS that the glideslope is out of service (OTS) for that runway'. This was confirmed when we heard approach tell another aircraft on 27L that it was OTS. Everything from this point on was uneventful until established on final other than specific speeds ATC was instructing us to fly. The swap to Tower went something like '[flight number] contact tower on 120.75; maintain 170 KIAS until TAFFS; contact Tower at TAFFS' (at this point we were about 5 miles from TAFFS). I'm not sure what all happened to lead to the event around TAFFS because I was heads down finishing [a] checklist and a lot was happening (contacting Tower; slowing to approach speed; finishing the checklist; etc). My assumption is that the Captain just put in too much of a descent rate with the AP (autopilot) at what would have been a normal glideslope intercept point. Tower contacted us and said 'low altitude alert check your altitude immediately' I looked up and saw 4 Red lights on the PAPI. At this point the Captain clicked off the AP and manually re-intercepted a proper visual glideslope. We were stable and checklist complete before 1000 and the landing was uneventful.Several factors contributed to this event. Late change of runway; glideslope being out of service; crunch point around TAFFS intersection compounded by ATC's request of speeds and radio communication; misapplication of AP descent rate at FAF; lack of crosscheck by the crew for adherence to recommended altitudes on the approach plate for 'LOC (GS out)'. Biggest thing would have been to brief the planned descent rate used by the AP based on the glideslope being out. Briefing and delegating adherence to the Recommended Altitudes for a LOC (GS out) approach. Anticipation of the crunch point around normal glideslope intercept and possibly an early slow/configuration to be stable at the point prior to intercepting a 3 deg glide path. AP usage and calculated descent rates for LOC approach. Cross-checking and communication by the FO for deviations based on those Recommended Altitudes.

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.