Incident Details
While in cruise flight, the flight crew detected a strange odor in the cockpit. Upon opening the cockpit door, the captain observed smoke in the courier area. The crew promptly donned oxygen masks and declared an emergency. They initiated a diversion to the nearest suitable airport.
Crew Actions
Shortly after the diversion was declared, the crew noticed heavy smoke emanating from the lavatory and heard a motor running continuously. In response, the captain discharged a Halon fire extinguisher into the lavatory compartment. The smoke subsequently subsided.
Post-Incident Findings
Post-incident examination of the aircraft revealed that the lavatory fan functioned normally. However, the recirculation fan, which is located beneath the lavatory, had seized. The seizure was caused by a failure of the motor end ball bearing located below the fan rotor. This allowed the motor rotor to make contact with the motor stator, generating the smoke observed by the crew.