Incident
During taxi to the departure runway, the pilot observed smoke in the cockpit area shortly after activating the heater ignition switch. The pilot immediately stopped the aircraft, secured it, and assisted the passengers in deplaning.
Examination
An inspection of the Janitrol heater, model B4050, found that the aft section of the tube assembly had cracked. The inner tube assembly was corroded, and a B-nut was only finger-tight. Fire damage was present in the nose section of the aircraft, near the heater.
Compliance
The director of maintenance stated that Airworthiness Directive AD-82-07-03, which required inspection of the heater tube assembly, had been complied with on November 14, 1983.