Preliminary Report: CRJ crew has bad vibrations

 - August 5, 2008, 8:39 AM

BOMBARDIER CL-600-2B19, CHATTANOOGA, TENN., MAY 8, 2003–At approximately 12:28 p.m. EDT Canadair Regional Jet N829AS encountered an uncommanded roll during cruise climb in VMC. The aircraft, registered to State Street Bank of Connecticut and operated by Atlantic Southeast Airlines, was operating as Flight 4690 on a Part 121 scheduled flight. The crew elected to make a precautionary diversion to Chattanooga. There were no injuries and the aircraft did not sustain any damage. The flight had departed Atlanta at 12:19 p.m. en route to Montreal.

According to investigators, the first officer (who was flying the aircraft) felt and heard a high-frequency vibration immediately after liftoff. The engine indication and crew alert system did not display any messages. When the airspeed was increased to 250 knots, the vibration started again. The pilot reported the vibration was slow and increased in intensity.

The captain contacted company maintenance while the first officer engaged the autopilot. The vibrations continued and lasted about 30 seconds. When the flight was cleared to 17,000 feet, the airplane started an uncommanded 45-degree roll to the right. The first officer disconnected the autopilot and regained control of the airplane. The captain declared an emergency and was issued radar vectors to Chattanooga. The first officer initiated a power-off descent while the captain monitored the instruments. The vibrations continued at all airspeeds during the descent and landing.

Examination of the right wing revealed the right aileron inboard and outboard power control unit output links exceeded the tolerance allowed when conducting the aileron control system backlash check and functionality test. The control links are being submitted to the NTSB Materials Laboratory for further analysis.