Air carrier on coupled ILS approach experienced aggressive pitch up and down.

Attributes
ACN	543495
Time
Date	200204
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : ord.airport
State Reference	IL
Altitude	agl single value : 1000
Environment
Flight Conditions	IMC
Weather Elements	Snow
Light	Dusk
Aircraft 1
Controlling Facilities	tower : ord.tower
Operator	common carrier : air carrier
Make Model Name	Fokker 100
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 9l
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	543495
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : less severe non adherence : published procedure other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	aircraft : equipment problem dissipated flight crew : overrode automation
Consequence	faa : reviewed incident with flight crew other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

On approach, autoplt engaged about 2 1/2 - 3 mi out on final. Aircraft pitched over aggressively in response to an immediate GS deviation to 1 DOT high, followed by an immediate return to 1 DOT low, and then a series of fluctuations reducing in range and back to solid on GS indication. Autoplt was disconnected at the initial onset and approach was flown via hand by first officer. Reported to tower and he reported he would report to his personnel.

Original NASA ASRS Text

Title: ACR ON COUPLED ILS APCH EXPERIENCED AGGRESSIVE PITCH UP AND DOWN.

Narrative: ON APCH, AUTOPLT ENGAGED ABOUT 2 1/2 - 3 MI OUT ON FINAL. ACFT PITCHED OVER AGGRESSIVELY IN RESPONSE TO AN IMMEDIATE GS DEV TO 1 DOT HIGH, FOLLOWED BY AN IMMEDIATE RETURN TO 1 DOT LOW, AND THEN A SERIES OF FLUCTUATIONS REDUCING IN RANGE AND BACK TO SOLID ON GS INDICATION. AUTOPLT WAS DISCONNECTED AT THE INITIAL ONSET AND APCH WAS FLOWN VIA HAND BY FO. RPTED TO TWR AND HE RPTED HE WOULD RPT TO HIS PERSONNEL.

Data retrieved from NASA's ASRS site as of July 2007 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.