MD-82
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Aircraft; Human Factors
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.
Some fixes were taken out of FMS anticipating a quicker turn on. All fixes should be left in until intercept.
MD-82 flight crew reported descending below charted altitude on approach to ORD when they lost situational awareness.