What happened
A chartered flight operated by Pascan Aviation Inc., involving a Beechcraft B100 with registration C-FLKS, departed Montréal/Saint-Hubert Airport for Bagotville, Quebec. The aircraft was carrying two passengers and two crew members. During the climb to 15,400 feet, the crew observed light smoke in the cabin, though no odor was detected.
In response to the smoke, the crew requested to level off at 17,000 feet and initiated emergency checklists. To mitigate the smoke, the crew eventually deactivated both bleed air valves at 9,000 feet, which caused the smoke to dissipate. The crew then declared an emergency and elected to return to Saint-Hubert rather than diverting to a closer airport. During the return, the aircraft experienced an electrical issue involving an inoperative inverter and a malfunctioning microphone, necessitating a change in pilot roles. The aircraft landed at 09:51 on Runway 24R with emergency services present. There were no injuries and no fire was reported.
The investigation
The investigation focused on the environmental system anomalies and the crew's response. Investigators found that the hot air ducts had been exposed to temperatures between 185°C and 200°C, exceeding safety limits. This thermal damage caused the ducts to perforate, allowing hot air to escape and create the visible smoke. The investigation also noted that the de-icer tube had collapsed due to the heat.
Regarding maintenance, investigators could not confirm when the damage occurred but noted that the Lexan 90434 polycarbonate material used in these specific ducts was more susceptible to heat damage than phenolic alternatives. There was also a concern that inspections of the air ducts might not have been performed according to the maintenance program, as similar damage had been found on other aircraft in the fleet.
Findings
- The primary cause of the smoke was the heat from the non-insulated bleed air line affecting the integrity of the air ducts.
- The polycarbonate material used for the hot air ducts was unable to withstand the extreme temperatures encountered during operation.
- The proximity of the bleed air line to the ducts and the de-icer tube led to the thermal degradation and subsequent perforation of the components.
- The crew's decision not to use oxygen masks and the decision to return to a more distant airport increased the period of risk exposure.