Date: 202109
Local time of day: 1801-2400
Location: ZZZ.TRACON, US
Aircraft: Regional Jet 900 (CRJ900)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Second aircraft: Regional Jet 900 (CRJ900)
Aircraft component: Aileron Control System
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Loss Of Aircraft Control
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We departed ZZZ [Runway] XXR on the ZZZZZ2 departure following Company Aircraft Y and Aircraft Z ahead of them. While attempting to initiate the turn to ZZZZZ; I found that I was unable to roll into a bank to the left. I added more aileron pressure and started adding trim to the left. Though I was not encountering any unusual resistance in the yoke; the aircraft was not rolling left. I reached and maintained about half control travel to the left. After a few seconds of this; I began to suspect a flight control problem and told the FO (First Officer) to select the flight controls synoptic page on the EICAS (Engine Indicating and Crew Alerting System). Almost simultaneously with the selection of the page; the plane began to respond to my aileron inputs. I only had the chance to observe the left side control positions before everything felt normal again; but I saw that the left aileron and both left multi-function spoilers were deflected upward as they should have been. I believe the full event lasted 15-20 seconds; and I believe I was holding half control deflection for 5-10 seconds.I honestly don't understand what happened. My two best guesses are wake turbulence or a transient aileron PCU (Power Control Unit) runaway; but both ideas seem unlikely. I don't believe Aircraft Y would produce enough wake to require that much aileron; and Aircraft Z was two planes ahead of us. It also seems unlikely to me that we would hit wake turbulence perfectly enough to experience such a consistent roll tendency for so long. An aileron PCU runaway seems unlikely to me because I don't know if that malfunction can be transient. Also; while I only had the chance to look at the flight control synoptic page as the event was ending; what I observed there looked normal for the control position I was holding.This probably was not an aircraft malfunction; but if similar incidents are reported; particularly in the same aircraft; I recommend inspecting the aileron system; and possibly the rudder system; although I did not feel any unusual yaw tendencies; nor did I observe anything amiss on my slip/skid indicator.




Synopsis: CRJ-900 Captain reported a transient left aileron malfunction described as aileron non-responsive to pilot's inputs.  The event lasted 15-20 seconds before returning to normal. Reporter did not provide any logical cause and no additional information provided.