Caravan 208B
Flight Crew Commercial
Distraction; Physiological - Other; Workload
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor; Flight Deck / Cabin / Aircraft Event Illness / Injury
Flight Crew Became Reoriented; Flight Crew Took Evasive Action; General Physical Injury / Incapacitation
Aircraft; Human Factors; Procedure
I had not flown this aircraft for several days so prior to the flight I did a pre-flight test of the TKS System in order to confirm its status. I ran the TKS System just long enough (approximately 3 to 4 minutes) to confirm the proper operation of the system components and to achieve a moderate purge of the panels. It was a warm morning; so prior to departing the ramp I opened the left side fuselage air vent for taxi; intending to close it before takeoff. After takeoff; having just leveled off within 5 to 6 minutes of takeoff with the TKS System turned OFF; I began to feel an irritation of my nose/throat and smelled a strong alcohol odor. I immediately realized that I had forgotten to close the side air vent before takeoff. Closing the left side air vent stopped the alcohol odor promptly and my nose/throat irritation dissipated a fairly short time later. I felt that there was no need for me to use the O2 mask in flight and chose to continue the day's flight legs with the TKS system turned OFF/fuselage side vents closed. The overhead/wing air vents were left open in flight throughout the day without any evidence of alcohol fumes in the cockpit. From past experience with the TKS system I feel confident that; even with the system turned OFF while in flight; residual TKS fluid in the supply lines from my ground test had drained down to the prop slinger from higher points in the system where it was sprayed into the air stream and entered the cockpit through the open fuselage air vent. Evidence of this fluid drain-down when the system; with no apparent check valves in the fluid supply lines; is turned off after having been run is clearly visible when an aircraft is parked after a flight during which the TKS System has been used. Large puddles of TKS fluid that collect on the ground under the prop and the fuselage strut attachment points are a normal occurrence lasting more than 24 hours after a TKS flight.In my experience this TKS System OFF fluid drain down and subsequent entry of the fluid spray into the air stream can result in TKS fumes being detected in the cockpit of an aircraft in flight that has a windshield or cockpit air leak.
The Reporter believes seven US and Canadian operators have TKS systems installed. The first reported concerns were from a Canadian operator. The TKS system is more a problem in high temperature operations than in cold weather as long as the windshield does not leak; the cockpit heater is OFF and the fuselage side vents are closed. In this condition TKS fluid have not entry avenue. Vaporized TKS fluid entering the cockpit through the heating system is not a problem for non-turbine powered C-208 aircraftThe system consists of two airfoil surface and propeller slinger pumps and two windshield pumps along with an extensive array of tubing about 100' total length. The fluid at the wing; tail and prop is about 4 psi and coats the wing after flowing through a membrane then microscopic laser drilled holes. When the pumps are OFF the fluid is prevented from flowing out the wing by dynamic air flow and so will seek the lowest system point which is the prop slinger. As a result; even after the system pumps are OFF; fluid can enter the cockpit through both the cockpit heated air; a leaking windshield or a fuselage vent; if open. After use in flight; the system continues to seep for a number of hours after landing because no in-line system check valves prevent static TKS fluid drainage. This is particularly a problem after system ground checks after which static leakage may occur for 24 hours or more. The system his designed to anti-ice but it does not work well. The slight amount of alcohol will de-ice and glycol will try to keep surfaces clear but C-208 pilots watch the airspeed and with accretion the speed will fall off; eventually forcing a pilot to lower flaps. A real problem is windshield accretion in heavy icing which cannot be cleaned by normal windshield system de-icing. A ground test is occasionally completed to ensure 75% of the wing is functioning. If not the aircraft cannot be dispatched into known or suspected weather. Pilots have learned to keep the cockpit heat OFF during TKS operation unless absolutely necessary. When they can no longer tolerate the cold the TKS system is activated and fluid will enter the engine intake and after heating will exit to the cockpit contaminating it. An option for pilots is an oxygen mask attached to the C-208 bottle. The problem is getting a mask ON and then communicating. The ship's mask it the full face unit; uncomfortable and not generally usable. There has been discussion about a vegetable based fluid call SUSTAIN but the Reporter does not know its status.
A C208B pilot reported TKS fluid odor from the prop slinger entered the cockpit after takeoff.  The reporter preflight tested the system; but failed to close the fuselage left air vent. Reporter noted that residual fluid drains for an extended period with TKS system OFF.