Date: 201202
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Aileron Control System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Troubleshooting; Situational Awareness; Time Pressure; Distraction; Confusion
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action; Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Flight Cancelled / Delayed; General Declared Emergency
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Approximately 200 miles from destination we were at FL260 and had just switched Centers. Aircraft started turning left while on autopilot. When unable to turn back to the right on automation the pilot flying disconnected the autopilot and flew manual. Pilot flying commented on how heavy and sluggish the controls felt. Pilot not flying informed ATC that we might have issues and please give us a heading while we sort this out. We complied with QRH Jammed/Restricted Flight Control procedure. About this time pilot not flying took control of the flight controls to get a feel of the problem. To the pilot not flying it felt very similar to manual reversion in the simulator. Pilot not flying then got a phone patch to Maintenance Control and asked for assistance to diagnose the problem. At this time the pilot flying said flight control pressures were getting worse. The pilot not flying terminated the phone patch and made an immediate command decision to declare an emergency and proceed to the nearest suitable airport. We were offered a nearby airport which we turned down and Dispatch suggested nearby larger airport. Pilot not flying briefed the (A) Flight Attendant for normal landing; nature of divert; then gave a PA to the passengers explaining precautionary landing for a flight control issue. [We] requested emergency vehicles to be on the ready; ran applicable checklists. Approach and landing [accomplished] safely and taxied in. Needed GPU; APU was on MEL. Passengers met by Agent and rebooked. I do not know why this happened. Because of the way the controls felt. Maybe the feel/centering Unit or electrical. Left flight spoiler was deployed and remained in the up position.

Callback: The Reporter stated that there was some cockpit crew friction as this event continued to develop. The First Officer insisted on diverting while the Captain would have elected to do a long slow descent to the destination. Because it was the First Officer's leg the Captain deferred to the First Officer who was exhibiting great concern for the aircraft's safety. The Reporter has made several calls attempting to determine exactly the cause and was only told a cable connected to an actuator failed and also the aileron feel sense unit was replaced.



Synopsis: A B737-400 ailerons became very sluggish and heavy in flight similar to manual reversion. An emergency was declared and the flight diverted to a nearby airport where an actuator cable was found failed and the aileron feel sense unit was also replaced.