NTSB Factual Report

On August 13, 2003, at 1450 eastern daylight time, a Bombardier Canadair CL600-2B19, N451CA, registered to and operated by Comair, Inc., as Flight 5374, had smoke in the cockpit shortly after takeoff from the Charleston International Airport, in Charleston, South Carolina. The flight diverted to Raleigh Durham International Airport, in Raleigh, North Carolina, and landed without further incident. The regularly scheduled revenue flight was being operated under the provision of Title 14 CFR Part 121 and instrument flight rules. Visual meteorological conditions prevailed, and an instrument flight plan was filed. The airline transport-rated captain, airline transport-rated first officer, flight attendant and 20 passengers were not injured, and the airplane sustained minor damage. The flight originated from Charleston, South Carolina, en route to LaGuardia, New York, on August 13, 2003 at 1415.

According to the flight crew, the flight pushed back from the gate in Charleston, South Carolina, about 1405. The crew reported heavy rain during boarding and pushback, and the airplane departed about 1415. With the captain as the pilot flying, the airplane climbed to a cruising altitude of flight level 270 with the autopilot engaged. About 1450, the crew reported hearing a loud thump, the airplane yawed to the right, and there was a loud buzzing sound as the air-driven generator deployed. The autopilot disengaged, and all six flight instrument and navigational screens went blank. After an estimated 20-seconds, the EFIS screens resumed operation and the engine indicating and crew alerting system (EICAS) showed that the #1 generator was inoperative. Acrid smoke entered the cockpit from near the feet of the Captain, prompting the use of oxygen masks and declaration of an emergency. The flight diverted to an uneventful landing at Raleigh Durham International Airport. The airplane was met and inspected by Airport Rescue and Fire Fighting personnel, and there were no signs of smoke or fire. The airplane taxied to the gate and the passengers deplaned through the main cabin door. A post-flight inspection revealed burned wiring and electrical components in the avionics compartment, beneath the cockpit.

Comair maintenance personnel found heat damage that centered around the left utility bus electrical relay. The burned relay with the most heat damage was found to be installed by Bombarier as the Utility Bus Relay, 1K4XD. Subsequently, the relay was identified as Hartman part number D-18ZZA. The heat damaged components and wiring were removed and submitted to the electrical laboratory at the Air Force Research Laboratory Materials Integrity Branch (AFRL/MLSA) for further examination.

According to the executive summary of the laboratory's report the examination revealed that all of the thermal damage, melting, charring and arcing, evidence indicate that a thermal event originated internally or on an external relay terminal. The most extensive damage occurred on the terminal one line side of the relay. There was no evidence found on the remaining exhibits to identify any of them as an initiation source for the failure.

NTSB Probable Cause

The failure of a utility bus relay which resulted in an electrical fire and subsequent smoke in the cockpit.