A320 flight crew experienced auto thrust malfunction during approach to runway 28 at ord. Auto thrus...

Narrative:

We were inbound and cleared for approach to 27L at ord with ap and at engaged on the ILS. ATC had assigned a speed of 250 KTS since we were still a good distance out. ATC offered us sidestep to runway 28. We said yes and they assigned us a heading of 10 degrees left to join the approach for 28. While on the new heading; the new approach was entered into the mcdu. At this point; the auto thrust (at) advanced so the plane started to accelerate. The pilot flying quickly reset the the FCU speed select window to a speed lower than 250 (actually 180). The at did not pull back the engines. The pilot flying then clicked off all automation and hand flew. By this point the plane had accelerated to about 275 KTS. Plane slowed with commendable pilot technique; continued in for normal landing on runway 28. Event written up in logbook. We spent a lot of time deconstructing the event during a post flight debrief. Also chatted with the mechanic and 2 other pilots. Various ideas put forth; but neither of us can specifically identify why the automation behaved this way.

Original NASA ASRS Text

Title: A320 flight crew experienced Auto Thrust malfunction during approach to Runway 28 at ORD. Auto Thrust added thrust while the flying pilot was attempting to slow. Control was regained by disconnecting Auto Thrust and retarding the thrust levers.

Narrative: We were inbound and cleared for approach to 27L at ORD with AP and AT engaged on the ILS. ATC had assigned a speed of 250 KTS since we were still a good distance out. ATC offered us sidestep to Runway 28. We said yes and they assigned us a heading of 10 degrees left to join the approach for 28. While on the new heading; the new approach was entered into the MCDU. At this point; the Auto Thrust (AT) advanced so the plane started to accelerate. The pilot flying quickly reset the the FCU speed select window to a speed lower than 250 (actually 180). The AT did not pull back the engines. The pilot flying then clicked off all automation and hand flew. By this point the plane had accelerated to about 275 KTS. Plane slowed with commendable pilot technique; Continued in for normal landing on Runway 28. Event written up in logbook. We spent a lot of time deconstructing the event during a post flight debrief. Also chatted with the mechanic and 2 other pilots. Various ideas put forth; but neither of us can specifically identify why the automation behaved this way.

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.

Attributes
ACN	893991
Time
Date	201006
Local Time Of Day	0601-1200
Place
Locale Reference	ORD.Airport
State Reference	IL
Aircraft 1
Make Model Name	A320
Flight Phase	Initial Approach
Component
Aircraft Component	Autothrottle/Speed Control
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Speed All Types Inflight Event / Encounter Loss Of Aircraft Control

A320 flight crew experienced auto thrust malfunction during approach to runway 28 at ord. Auto thrust added thrust while the flying pilot was attempting to slow. Control was regained by disconnecting auto thrust and retarding the thrust levers.