Mid Atlantic Freight Cessna 208B incident

The pilot executed an emergency landing after reporting smoke in the cockpit. The aircraft sustained minor damage during the incident. The pilot was treated at a local hospital and released. Shortly before landing the pilot reported noticing smoke in the cockpit. He reported he opened a vent, which cleared the smoke, and subsequently landed without incident. After landing, however, the vent did not adequately clear the smoke. He taxied to the ramp and emergency personnel assisted him from the aircraft. Rescue personnel reportedly examined the aircraft for the source of the smoke. Although they noted an occasional odor, it was not strong enough to indicate a definite origin. There was no evidence of a fire. A post-incident review determined the engine bleed air pressure regulator had failed, allowing unregulated bleed air into the deice system. The temperature of the unregulated P3 air may be as high as 607 degrees Fahrenheit. The bleed air is routed through a supply line which runs through the left side door post. The line is constructed of thin-walled aluminum tubing and is wrapped in anti-chaffing tape. The source of the smoke was the tape which became overheated due to the unregulated bleed air. The pressure regulator and pneumatic supply line were replaced. The aircraft was subsequently returned to service and, after monitoring several flights, the problem did not recur.

Verbatim NTSB analysis and probable cause from the NTSB dataset