Md-83 flight crew reported encountering tail ice on approach to ord resulting in a 400 ft altitude d...

Narrative:

Right downwind ord 27R descending in heavy icing conditions. Aircraft encountered heavy ice in the descent between 8000 and 4000 ft. Engine and wing anti-ice had been selected 'on' before entering icing conditions appoximately 5 minutes prior to event. Tail deice had not been activated at this point. Aircraft was level at 4000 ft and 250 kts.ATC issued us to slow to 210 kts and a 90 degree right turn to heading 180. The combination of flaps being extended; a 25 degree bank turn and ice on tail prevented the slow speed trim from keeping up with nose down tendencies. Aircraft started to sink rapidly in the turn. Upon realization that the autopilot was not satisfactorily flying the airplane; the autopilot was disconnected as well as autothrottles. The aircraft was in a extreme out of trim nose down situation.corrective inputs were applied and required aggressive correction to stop the sink. By the time the aircraft was recovered and climbing; we had lost 400 ft. The tail deice was applied and the autopilot was engaged for a normal ILS approach. In heavy icing conditions; the tail deice needs to be run more often.

Original NASA ASRS Text

Title: MD-83 flight crew reported encountering tail ice on approach to ORD resulting in a 400 FT altitude deviation.

Narrative: Right downwind ORD 27R descending in heavy icing conditions. Aircraft encountered heavy ice in the descent between 8000 and 4000 ft. Engine and Wing anti-ice had been selected 'on' before entering icing conditions appoximately 5 minutes prior to event. Tail deice had not been activated at this point. Aircraft was level at 4000 ft and 250 kts.ATC issued us to slow to 210 kts and a 90 degree right turn to heading 180. The combination of flaps being extended; a 25 degree bank turn and ice on tail prevented the slow speed trim from keeping up with nose down tendencies. Aircraft started to sink rapidly in the turn. Upon realization that the autopilot was not satisfactorily flying the airplane; the autopilot was disconnected as well as autothrottles. The aircraft was in a extreme out of trim nose down situation.Corrective inputs were applied and required aggressive correction to stop the sink. By the time the aircraft was recovered and climbing; we had lost 400 ft. The tail deice was applied and the autopilot was engaged for a normal ILS approach. In heavy icing conditions; the tail deice needs to be run more often.

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.

Attributes
ACN	1223973
Time
Date	201412
Local Time Of Day	1201-1800
Place
Locale Reference	C90.TRACON
State Reference	IL
Aircraft 1
Make Model Name	MD-83
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter Weather / Turbulence

Md-83 flight crew reported encountering tail ice on approach to ord resulting in a 400 ft altitude deviation.