Narrative:

ATC informed us that there was reported light to moderate icing from FL185 to FL225. We were in moderate icing from 14;500 to approximately FL270. We had engine and wing anti-ice systems on and operating. We were both very concerned about the amount of ice building on the airplane as evidenced by the significant amount building on the probe between the windscreens and all of the way around the two front windscreens. I selected maximum continuous thrust (mct) at about FL180 to facilitate climbing through the icing more quickly. Our clearance was to FL230 which was set in the FCU window with the autopilot flying. We were both significantly distracted talking about and observing the icing and also coming up with a plan of action; that our brains were focused on climbing out of the icing. So when the autopilot leveled off at FL230; the airplane kept accelerating since we were still in mct. Thinking we were getting unreliable airspeed due to icing; and expecting to keep climbing instead of being level; I disconnected the autopilot and pulled up. The altitude alert went off at 23;300 ft and I realized what happened and started back down to FL230 after reaching 23;400 ft. Also contributing was that during the climbout; the vvi (vertical velocity indicator) fluctuated between -300 and +1;100; so seeing the vvi at 0 was somewhat expected in the back of my mind. Our concern was the unknown amount and weight of the ice on the unheated parts of the airplane since the ice did not sublimate enroute.

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Original NASA ASRS Text

Title: A320 flight crew becomes concerned with ice build up during climb and selects MCT to expedite the climb. When the autopilot levels off at FL230 the aircraft rapidly accelerates. The pilot flying disengages the autopilot and begins to climb before the altitude chime alerts him to the altitude clearance and that the MCT setting is causing the airspeed increase.

Narrative: ATC informed us that there was reported light to moderate icing from FL185 to FL225. We were in moderate icing from 14;500 to approximately FL270. We had engine and wing anti-ice systems on and operating. We were both very concerned about the amount of ice building on the airplane as evidenced by the significant amount building on the probe between the windscreens and all of the way around the two front windscreens. I selected Maximum Continuous Thrust (MCT) at about FL180 to facilitate climbing through the icing more quickly. Our clearance was to FL230 which was set in the FCU window with the autopilot flying. We were both significantly distracted talking about and observing the icing and also coming up with a plan of action; that our brains were focused on climbing out of the icing. So when the autopilot leveled off at FL230; the airplane kept accelerating since we were still in MCT. Thinking we were getting unreliable airspeed due to icing; and expecting to keep climbing instead of being level; I disconnected the autopilot and pulled up. The altitude alert went off at 23;300 FT and I realized what happened and started back down to FL230 after reaching 23;400 FT. Also contributing was that during the climbout; the VVI (Vertical Velocity Indicator) fluctuated between -300 and +1;100; so seeing the VVI at 0 was somewhat expected in the back of my mind. Our concern was the unknown amount and weight of the ice on the unheated parts of the airplane since the ice did not sublimate enroute.

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.