What happened
During cruise flight, the crew detected an unusual odor within the cabin. Upon opening the cockpit door, the captain observed smoke in the courier area. In response to the developing situation, the crew donned oxygen masks and declared an emergency, subsequently diverting the aircraft to the nearest suitable airport.
As the flight continued, the crew noticed heavy smoke emanating from the lavatory area and heard a motor running continuously. To combat the smoke, the captain discharged a Halon fire extinguisher into the lavatory compartment, which caused the smoke to subside.
The investigation
A post-incident examination of the aircraft systems was conducted. The investigation determined that while the lavatory fan was functioning normally, the recirculation fan located beneath the lavatory had seized. Specifically, the motor end ball bearing, situated below the fan rotor, had failed. This failure allowed the motor rotor to make contact with the motor stator.