NTSB Factual Report

On March 18, 2003, at 2225 eastern standard time, a Cessna 208B (Caravan), operated by Mid Atlantic Freight Inc. and piloted by a commercial pilot, experienced smoke in the cockpit. The aircraft sustained minor damage during the incident. The pilot executed an emergency landing on runway 5 (8,002 feet x 150 feet, asphalt) at MBS International Airport (MBS), Saginaw, Michigan. MBS was the intended destination. The 14 CFR Part 135 cargo flight was operating on an instrument flight rules (IFR) flight plan at the time of the incident. Visual meteorological conditions prevailed. The pilot sustained minor injuries. The flight departed Cherry Capital Airport (TVC), Traverse City, Michigan, about 2145.

The pilot's written statement noted that, prior to landing at MBS, he noticed a "sweet smell in the cockpit." He stated he did not notice any smoke at that time. However, a few minutes later, he turned on a flashlight and noticed a slight haze in the cockpit. He reported he opened a vent, which cleared the smoke. He subsequently landed without incident.

After landing, however, the vent did not adequately clear the smoke, according to the pilot. He noted that he taxied to the ramp and emergency personnel assisted him from the aircraft. He reported being taken to a nearby hospital, where he was treated and released.

Airport fire and rescue personnel reported that the pilot drifted "in and out of conciousness" upon exiting the aircraft. The aircraft was reportedly examined for the source of the smoke. Although they noted an occasional odor, it was not strong enough to indicate a definite location, according to the incident report. No evidence of a fire was reported.

The pilot reported similar incidents occurred twice before, although not as severe. Each time the problem was referred to a mechanic and the pilot reported he was told the problem had been fixed.

A post-incident review by a mechanic determined the pneumatic supply line for the aircraft deice boots started to smoke after about 10 minutes with the engine running at a high power setting. Further investigation 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, according to the manufacturer.

The supply line is routed from the engine, through the left side door post, to the left wing. The line is constructed of thin-walled aluminum tubing and is wrapped in anti-chaffing tape, according to the aircraft manufacturer. The mechanic stated the source of the smoke was the tape.

The pressure regulator and pneumatic supply line were replaced. Additional damage to the outboard deice boot on the left wing was repaired. The aircraft was subsequently returned to service and, after monitoring several flights, the problem did not recur.

NTSB Probable Cause

Failure of the engine bleed air pressure regulator. A contributing factor was the anti-chaffing tape on the air supply line.