Incident Overview
On April 18, 2010, at approximately 0653 central daylight time, a Bombardier CL-600-2C10, registration N160GJ, encountered a control system anomaly during cruise flight. The aircraft was operating as United Express Flight 7374, a domestic passenger flight under 14 CFR Part 121, operated by Go-Jet Airlines. The flight crew diverted to Kansas City International Airport (MCI) in Kansas City, Missouri, where an uneventful landing was performed. There were no injuries to passengers or crew, and no damage to the airplane.
Flight Details
The flight originated from Will Rogers World Airport (OKC) in Oklahoma City, Oklahoma, at approximately 0600 central daylight time, en route to Chicago O'Hare International Airport (ORD) in Chicago, Illinois. Instrument meteorological conditions prevailed, and the flight operated under an instrument flight rules flight plan. After departure in heavy rain, the aircraft was cleared to climb to flight level 350 (35,000 feet pressure altitude).
Control System Anomaly
About 20 minutes into the flight, the flight crew noticed that the airplane was not turning properly to a planned waypoint. A red "A" appeared on the flight display, indicating excessive aileron forces. The captain disconnected the autopilot and attempted manual control of the ailerons, finding excessive forces and limited response. The crew attempted a roll disconnect, which separates the left and right control wheels, but no improvement was detected. The flight crew decided to divert to MCI. During descent through approximately 15,000 feet, the ailerons "broke free" and returned to normal forces. The flight crew made an uneventful landing.
Flight data recorder (FDR) data indicated that the ailerons responded normally during initial flight control checks and early portions of the flight. About 11 minutes into the flight, the airplane encountered ambient temperatures below 32 degrees Fahrenheit. During climb, about 20 minutes into the flight, the left aileron response became abnormal and did not respond properly to autopilot inputs, while the right aileron remained responsive. After the autopilot was disconnected and manual inputs attempted, control wheel forces near 25 pounds resulted in minimal movement of both ailerons, indicating binding in the aileron control system. The roll disconnect was pulled, but both control circuits remained bound. As the airplane descended through about 20,000 feet, the left control wheel experienced a force of 34 pounds for 6 seconds, after which the left aileron broke free. The remainder of the flight was flown using the left control wheel. Shortly thereafter, ambient temperature rose above 32 degrees Fahrenheit.
Post-Event Examination
Examination of the aileron control system by the operator following the event revealed no anomalies in the aileron control system.