NTSB Factual Report

On April 18, 2010, about 0653 central daylight time, a Bombardier CL-600-2C10, N160GJ, experienced a control system anomaly during cruise flight. The airplane diverted to the Kansas City International Airport, Kansas City, Missouri, where an uneventful landing was performed. There were no injuries to the passengers or crew, and no damage to the airplane. The aircraft was registered to and operated by Go-Jet Airlines as United Express Flight 7374, under the provisions of 14 Code of Federal Regulations Part 121 as domestic passenger flight. Instrument meteorological conditions prevailed for the flight, which operated on an instrument flight rules flight plan. The flight originated from the Will Rogers World Airport, Oklahoma City (OKC), Oklahoma about 0600 and was en route to the Chicago O'Hare International Airport, Chicago, Illinois when the event occurred.

The operator reported that the airplane departed OKC in heavy rain and was cleared to climb to flight level (FL) 350 (35,000 feet pressure altitude). About 20 minutes into the flight, the flight crew noticed that the airplane was not turning properly to a planned waypoint along the intended route of flight. A red “A” appeared on the flight display indicating excessive aileron forces. The Captain disconnected the autopilot and attempted manual control of the ailerons. He found that aileron forces were excessive and response to aileron control was limited. The flight crew attempted a “roll disconnect” which disengages the right and left control wheels. During operation with the roll disconnect pulled, the right control wheel controls only the right aileron, and the left control wheel controls only the left aileron, and the left and right control wheels do not move in unison. No improvement was detected. The flight crew elected to divert to MCI. Upon descending through about 15,000 feet altitude the ailerons “broke free” and returned to normal forces. An uneventful landing was made at MCI.

According to flight data recorder (FDR) data, the airplane’s ailerons responded normally during flight control checks and during the initial portions of the flight. About 11 minutes into the flight, the airplane encountered ambient temperatures that were below 32 degrees Fahrenheit. During climb, about 20 minutes into the flight, FDR data indicates that the left aileron response was abnormal and was not responding properly to autopilot inputs. The right aileron was responsive to autopilot inputs. The FDR data showed that about 25 minutes into the flight, the autopilot was disconnected and manual control wheel inputs attempted. The data showed that control wheel input forces near 25 pounds resulted in minimal movement of both ailerons which is indicative of binding in the aileron control system. About 27 minutes into the flight, the roll disconnect handle was pulled. Subsequent control wheel inputs indicate that the right and left aileron control circuits remained bound. The FDR data showed that as the airplane descended through about 20,000 feet altitude, the left control wheel force was 34 pound for 6 seconds at which time the left aileron broke free. The remainder of the flight was flown using the left control wheel. A few minutes later, the ambient temperature rose above 32 degrees Fahrenheit.

Examination of the aileron control system by the operator subsequent to the event revealed no anomalies in the aileron control system.

NTSB Probable Cause

The malfunction of the airplane’s aileron control system due to ice accumulation.