Narrative:

On descent into lax out of FL300 on the SEAVU2 arrival the FMGC in our aircraft would not hold the programmed airspeed entered in the perf descent page (ATC assigned 300+ knots; then later assigned 280 KIAS). I tried several times to select managed speed and was forced by the aircraft (it was pitching up trying incorrectly to achieve 250 KIAS) to return to selected speed and after three attempts found myself almost 1;000 ft above path. (I wrote up the anomalies upon arrival in lax).in order to make my restriction of 17;000 ft/280 KTS at konzl; I selected full speed brakes and disconnected the autopilot (in order to get full spoiler deflection). We monitored our speed and vertical path and managed to meet the constraint airspeed and altitude at konzl. As we approached engli we noticed that we were starting to descend below the constraint altitude approximately two and a half miles prior to the fix. I pushed V/south to stop our descent and was surprised that we continued a gentle descent. At the same time we noticed that the navigation display was indicating that we were 0.3 miles right of course centerline. At this time the first officer noticed that we were not following the flight director. I realized that after stowing the speed brake we had never reengaged the autopilot and the airplane had been tracking pitch and roll attitude in control wheel steering since the speed brakes had been stowed.we crossed close abeam engli at approximately 15;600 ft (almost 400 ft below constant altitude). A quick visual scan and scan of the TCAS indicated that we were not in danger of a midair collision. A gentle correction to our descent rate reestablished us on path and the autopilot was reengaged. We advised ATC that we were going to miss our altitude constraint at engli. The rest of the approach was flown within parameters and without incident.the event was caused by our distraction with equipment malfunction and failure to remain aware of the autopilot disconnect. Because control wheel steering is the automatic default in the A320 it can easily be mistaken for an autopilot engaged mode.we needed better delineation of pilot flying and pilot not flying duties. Only close attention to the path allowed us to catch it (the autopilot disconnect) as early as we did.

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Original NASA ASRS Text

Title: An A320 Captain discussed the effects of flight crew confusion and distraction associated with a malfunctioning vertical navigation programming on flight path control and situational awareness.

Narrative: On descent into LAX out of FL300 on the SEAVU2 arrival the FMGC in our aircraft would not hold the programmed airspeed entered in the perf descent page (ATC assigned 300+ knots; then later assigned 280 KIAS). I tried several times to select managed speed and was forced by the aircraft (it was pitching up trying incorrectly to achieve 250 KIAS) to return to selected speed and after three attempts found myself almost 1;000 FT above path. (I wrote up the anomalies upon arrival in LAX).In order to make my restriction of 17;000 FT/280 KTS at KONZL; I selected full speed brakes and disconnected the autopilot (in order to get full spoiler deflection). We monitored our speed and vertical path and managed to meet the constraint airspeed and altitude at KONZL. As we approached ENGLI we noticed that we were starting to descend below the constraint altitude approximately two and a half miles prior to the fix. I pushed V/S to stop our descent and was surprised that we continued a gentle descent. At the same time we noticed that the NAV display was indicating that we were 0.3 miles right of course centerline. At this time the First Officer noticed that we were not following the Flight Director. I realized that after stowing the speed brake we had never reengaged the autopilot and the airplane had been tracking pitch and roll attitude in Control Wheel Steering since the speed brakes had been stowed.We crossed close abeam ENGLI at approximately 15;600 FT (almost 400 FT below constant altitude). A quick visual scan and scan of the TCAS indicated that we were not in danger of a midair collision. A gentle correction to our descent rate reestablished us on path and the autopilot was reengaged. We advised ATC that we were going to miss our altitude constraint at ENGLI. The rest of the approach was flown within parameters and without incident.The event was caused by our distraction with equipment malfunction and failure to remain aware of the autopilot disconnect. Because Control Wheel Steering is the automatic default in the A320 it can easily be mistaken for an autopilot engaged mode.We needed better delineation of pilot flying and pilot not flying duties. Only close attention to the path allowed us to catch it (the autopilot disconnect) as early as we did.

Data retrieved from NASA's ASRS site as of July 2013 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.