An ERJ170 captain described pitch oscillations after encountering ice on approach with his autopilot...

Attributes
ACN	824501
Time
Date	200902
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	IMC
Aircraft 1
Make Model Name	EMB ERJ 170/175 ER&LR
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Other Instrument Precision
Flight Plan	IFR
Component
Aircraft Component	Autopilot
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Inflight Event / Encounter Other / Unknown

Narrative:

We were intercepting the GS at 5;000 ft around zzzzz. We were on the localizer and told to slow down from 190 KTS to 170 KTS. We were experiencing light rime icing with autopilot on. As I dialed in 170 KTS; I called for flaps 3 degrees. We were either just intercepting the GS; or had recently intercepted it. As flaps 3 degrees was put in; the airplane began its usual pitching action; but we noticed it was getting to be unusual. The pitch actually increased so much at one point (the plane dipped slightly below the GS); that our vertical path angle was about 3-4 degrees. I am unsure of what our pitch attitude was; but it was unusually high; especially since we were just descending on the GS. I immediately disconnected the autopilot and hand flew the rest of the approach with no difficulty. In light of recent events; I thought it would be prudent to pass on this information and made a report of it to the chief pilot in case flight fdr data was needed.

Original NASA ASRS Text

Title: An ERJ170 Captain described pitch oscillations after encountering ice on approach with his autopilot on. He disconnected the autopilot and landed with no difficulty.

Narrative: We were intercepting the GS at 5;000 FT around ZZZZZ. We were on the LOC and told to slow down from 190 KTS to 170 KTS. We were experiencing light rime icing with autopilot on. As I dialed in 170 KTS; I called for flaps 3 degrees. We were either just intercepting the GS; or had recently intercepted it. As flaps 3 degrees was put in; the airplane began its usual pitching action; but we noticed it was getting to be unusual. The pitch actually increased so much at one point (the plane dipped slightly below the GS); that our vertical path angle was about 3-4 degrees. I am unsure of what our pitch attitude was; but it was unusually high; especially since we were just descending on the GS. I immediately disconnected the autopilot and hand flew the rest of the approach with no difficulty. In light of recent events; I thought it would be prudent to pass on this information and made a report of it to the Chief Pilot in case flight FDR data was needed.

Data retrieved from NASA's ASRS site as of April 2012 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.

An ERJ170 captain described pitch oscillations after encountering ice on approach with his autopilot on. He disconnected the autopilot and landed with no difficulty.