Narrative:

Weather scattered about 4;500 feet could not see the airfield but could see the ground clearly. On final runway 10C outside of sharn cleared the ILS 10C maintain 5;000 until sharn. Lost GS signal on final; thought we were closer to airport than actual distance; used vertical speed (vs) to start descent at 700 feet/minute; could not ask about GS signal due to radio very busy; as we got below the scattered cloud deck could see we were low for our distance to the airfield; ended up being about 3;200 feet prior to rruda; climbed back up to 4;000 feet and intercepted the GS at rruda and landed.put all fixes in the FMS prior to approach for situational awareness.

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Original NASA ASRS Text

Title: MD-82 flight crew reported descending below charted altitude on approach to ORD when they lost situational awareness.

Narrative: Weather scattered about 4;500 feet could not see the airfield but could see the ground clearly. On final Runway 10C outside of SHARN cleared the ILS 10C maintain 5;000 until SHARN. Lost GS signal on final; thought we were closer to airport than actual distance; used Vertical Speed (VS) to start descent at 700 feet/minute; could not ask about GS signal due to radio very busy; as we got below the scattered cloud deck could see we were low for our distance to the airfield; ended up being about 3;200 feet prior to RRUDA; climbed back up to 4;000 feet and intercepted the GS at RRUDA and landed.Put all fixes in the FMS prior to approach for situational awareness.

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.