A319 flight crew reported an abrupt; uncommanded pitch up and climb when the FMS was set up for a ma...

Narrative:

We were given a clearance to descend via the arrival into ZZZ and were at FL370. We also were instructed to maintain 270 kts until zzzzz intersection and then resume published speeds. 6;000 ft had been put into the altitude window for the bottom altitude of the profile descent and des was indicated on the FMA for a managed descent. Aircraft was being operated with autopilot 2 engaged. First officer was PF and is a new hire. We were both looking at the first officer's mcdu as I was explaining how to put the 270 knot restriction on the des page. We both felt the plane abruptly pitch up and begin a zoom climb and depart FL370. I looked at all the instruments to determine why the aircraft started the climb; initially believing that a protection had been activated or we had suffered an undue activation of alpha protection malfunction; but neither was the case. Ap never disengaged on its own. Ap was disconnected and aircraft was leveled at about 38;800 ft then a descent was begun. I advised ATC of the event. Ap 2 was then reengaged. It appeared that the aircraft was starting to climb again so ap 2 was again disconnected. We engaged ap 1 and resumed normal operations on that autopilot.

Original NASA ASRS Text

Title: A319 flight crew reported an abrupt; uncommanded pitch up and climb when the FMS was set up for a Managed Descent using Autopilot Number Two. Normal operations were resumed with the use of Autopilot One.

Narrative: We were given a clearance to descend via the arrival into ZZZ and were at FL370. We also were instructed to maintain 270 kts until ZZZZZ intersection and then resume published speeds. 6;000 ft had been put into the altitude window for the bottom altitude of the profile descent and DES was indicated on the FMA for a managed descent. Aircraft was being operated with autopilot 2 engaged. FO was PF and is a new hire. We were both looking at the FO's MCDU as I was explaining how to put the 270 knot restriction on the DES page. We both felt the plane abruptly pitch up and begin a zoom climb and depart FL370. I looked at all the instruments to determine why the aircraft started the climb; initially believing that a protection had been activated or we had suffered an undue activation of alpha protection malfunction; but neither was the case. AP never disengaged on its own. AP was disconnected and aircraft was leveled at about 38;800 ft then a descent was begun. I advised ATC of the event. AP 2 was then reengaged. It appeared that the aircraft was starting to climb again so AP 2 was again disconnected. We engaged AP 1 and resumed normal operations on that autopilot.

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	1446762
Time
Date	201705
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.Airport
State Reference	US
Aircraft 1
Make Model Name	A319
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Component
Aircraft Component	Autopilot
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude

A319 flight crew reported an abrupt; uncommanded pitch up and climb when the FMS was set up for a managed descent using autopilot number two. Normal operations were resumed with the use of autopilot one.