Date: 201401
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Dusk
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Aileron Trim System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Human-Machine Interface
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Aircraft Equipment Problem Dissipated; Flight Crew Diverted; Flight Crew Landed As Precaution; General Declared Emergency
Contributing factors: Aircraft; Human Factors
Primary problem: Ambiguous

Narrative: The event occurred while in cruise at FL360. We were approximately one hour from the original destination. The Captain was using the lavatory and the flight attendant was on the flight deck with me. I noticed that the roll trim was right of center and so I briefly actuated the roll trim to the left in an attempt to re-center it. Immediately; the autopilot disengaged and the aircraft quickly and sharply rolled to the right. I took control of the aircraft and leveled the wings. I tried to re-engage the autopilot but once again; it disconnected and the aircraft rolled to the right for a second time. Once again; I leveled the wings and hand flew the aircraft. The Captain quickly re-entered the flight deck. We ran the memory items for the aileron hardover/roll trim runaway. We followed up with the Immediate Action checklist which then led us to the appropriate QRH procedure. We declared an emergency; began a descent out of RVSM airspace; and asked ATC to find us a destination which was VFR. In the interest of safety; we decided not to continue to destination which was IFR with low clouds and snow. We also asked ATC for right hand turns only. The decision was made to land at ZZZ which was just over 100 miles away. The weather conditions there indicated VFR with 10 miles visibility; high clouds; and no precipitation. We asked for the longest runway. The Captain briefed the Flight Attendant and the passengers. A message was sent to Dispatch via ACARS. We took turns hand flying the aircraft which was a fatiguing task because of its tendency to roll to the right. Once we were established on course; the QRH was complete; and the approach had been briefed; the Captain decided to attempt to actuate the roll trim in an attempt to re-center it. It worked. The roll trim returned to center and the remainder of the flight was essentially normal. The Captain continued to hand fly the aircraft and the landing was uneventful. We exited the runway and coordinated with operations for a gate. One threat was that I was the only pilot in the flight deck during the moment of the trim runaway. Another threat was bad weather at our destination. We mitigated that particular threat with the decision to find a VFR airport for landing. An error on my part was attempting to correct the trim back toward center while being the only pilot on the flight deck. The smarter choice would have been to wait for the Captain to come back and discuss it before I tried to address the problem. The undesired aircraft state was an un-commanded bank at FL360. This event reiterated the need for having memory items! I actually had flown this scenario in the simulator during new hire training and I'm thankful for that. I remember how difficult the simulator was to control without hydraulic assistance to the ailerons. That simulator event definitely prepared me for this real life situation. Although I'm sure my performance wasn't stellar; overall I'm pleased with how the Captain and I handled the situation. First and foremost; I kept the wings level until the Captain re-entered the flight deck. From that point on we worked together effectively to complete the QRH and land safely.




Synopsis: EMB145 First Officer experiences runaway aileron trim at FL360 with the Captain in the lavatory. The Captain quickly enters the cockpit and the decision is made to divert to the nearest suitable airport. During the descent a second attempt is made to center the aileron trim which is successful.