Narrative:

Ops normal in cruise at FL350. Began to pick up what felt like light chop. We noticed within a few minutes that the characteristics of the chop were unusual. 1.the aircraft only moved in pitch-absolutely no role or yaw. 2.the chop was a very consistent 'bump' that occurred on a cycle of 10-15 seconds. We pulled up the F/ctrl display on the sd. Immediately we noticed that both the left and right aileron indices were moving in sync with the bump. Both indices would move up and down rapidly 1/16 to 1/8 of an inch of total travel on the synoptic as each bump was felt. Applying systems knowledge; we knew that ELAC1 normally controlled the ailerons. During preflight planning; we had noted that this particular aircraft had just had ELAC1 replaced after multiple write-ups for ELAC1 fault and ail servo ecams in flight. Accordingly; I pulled out the FM and reviewed the F/control elac 1/2 fault irregular. It reads: one computer failed: caution: do not reset elac if uncommanded maneuvers occurred during flight. Elac (affected)...off then on based on the uncommanded pitch motion; the maintenance history of the aircraft; my systems knowledge and the caution above; I decided that the safest course of action was to turn off ELAC1. The first officer disconnected autopilot and was hand flying as I turned off ELAC1. Aileron movement and pitch bump stopped immediately and did not recur for the remainder of the flight. We contacted dispatch via ACARS and added maintenance to the patch. I described situation and agreed to make maintenance write up as we continued to destination. I also reminded dispatch that we were now downgraded to cat 2 status with the ELAC1 turned off. The rest of the flight was routine to landing.

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Original NASA ASRS Text

Title: A320 Flight Crew experiences what is described as bump or rhythmic light chop at FL350. While checking the Flight Control page it is discovered that the bump is in sync with aileron movement. Due to the maintenance history of the aircraft; the Captain elects to turn of ELAC1 and the bump immediately disappears.

Narrative: Ops normal in cruise at FL350. Began to pick up what felt like light chop. We noticed within a few minutes that the characteristics of the chop were unusual. 1.The aircraft only moved in pitch-absolutely no role or yaw. 2.The chop was a very consistent 'bump' that occurred on a cycle of 10-15 seconds. We pulled up the F/CTRL display on the SD. Immediately we noticed that both the left and right aileron indices were moving in sync with the bump. Both indices would move up and down rapidly 1/16 to 1/8 of an inch of total travel on the synoptic as each bump was felt. Applying systems knowledge; we knew that ELAC1 normally controlled the ailerons. During preflight planning; we had noted that this particular aircraft had just had ELAC1 replaced after multiple write-ups for ELAC1 Fault and Ail Servo ECAMS in flight. Accordingly; I pulled out the FM and reviewed the F/CTL ELAC 1/2 Fault Irregular. It reads: One computer failed: CAUTION: Do not reset ELAC if uncommanded maneuvers occurred during flight. ELAC (affected)...OFF THEN ON Based on the uncommanded pitch motion; the maintenance history of the aircraft; my systems knowledge and the caution above; I decided that the safest course of action was to turn off ELAC1. The First Officer disconnected autopilot and was hand flying as I turned off ELAC1. Aileron movement and pitch bump stopped IMMEDIATELY and did not recur for the remainder of the flight. We contacted Dispatch via ACARS and added Maintenance to the patch. I described situation and agreed to make maintenance write up as we continued to destination. I also reminded Dispatch that we were now downgraded to Cat 2 status with the ELAC1 turned off. The rest of the flight was routine to landing.

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.