What happened
On June 5, 2002, a Rockwell Commander 690C, registration SE-GSS, was conducting an aerial photography mission near Örebro airport, Sweden. During the climb to 22,000 feet, the pilot noticed an odor that was initially mistaken for cleaning residue. This smell quickly intensified into visible smoke emerging from both sides of the instrument panel.
In response to the developing situation, the pilot initiated an immediate descent to land at the nearest suitable airfield, Örebro airport. During the approach, the crew utilized a halon fire extinguisher to attempt to suppress the smoke. The aircraft landed safely, and the pilot promptly deactivated the main electrical power. Airport rescue teams met the aircraft upon arrival to manage the smoke emissions.
The investigation
The Swedish Accident Investigation Board (SHK) examined the aircraft's side window defogger system and its components. The investigation focused on the heating elements, the airflow mechanism, and the maintenance protocols governing the equipment. Investigators also reviewed the pilot's response and the operator's training procedures.
Findings
Technical examination revealed that the instrument panel glareshield had melted in two areas directly above the left and right heaters of the side window deflagration system. The investigation established that the defogger heaters overheated because the fan responsible for supplying airflow to the system had failed. Specifically, a worn-out motor brush had rendered the fan inoperable.
While the system included thermostats designed to disconnect the heaters if temperatures exceeded 50°C, these failed to act as protection because they were positioned in a way that they were not affected by the localized heat buildup. Furthermore, the investigation found that the aircraft's maintenance program did not require periodic servicing of the fan or its motor, which allowed the component failure to go undetected.
Additionally, the pilot did not utilize the onboard emergency checklist or don oxygen masks during the event. The investigation noted that the operator lacked a structured plan for systematic emergency training, which may have contributed to the crew's high workload and decision-making during the incident.
Safety action
The SHK recommended that the Swedish Civil Aviation Administration work toward revising both the aircraft type's design and its maintenance program. The goal is to ensure that a fan failure does not create a fire risk and to reduce the likelihood of such fan failures occurring through improved maintenance oversight.