Cessna Stationair/Turbo Stationair 6
Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Commercial
Flight Crew Last 90 Days 50; Flight Crew Total 2400; Flight Crew Type 1900
Aircraft Equipment Problem Critical
Air Traffic Control Issued New Clearance; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport
Human Factors; Aircraft
This was the coldest morning of a record setting cold streak. The weather station on the field recorded an overnight low of 23 degrees F. My crew (camera operator) and I arrived at the field to preflight for our photo mission at XA:30 AM. The aircraft received no preheating; but was in a hangar overnight. ATIS was reporting 4 degrees C (about 37 F) at the time of engine start. After an extra long engine run-up to ensure CHT and oil temps were well into the green arc; and an otherwise normal run-up check; we departed. Seconds after passing over the departure end of the runway; at an altitude of about 400-500 feet AGL; the engine starting running extremely rough; coughing; surging; and losing power. I asked the Tower for immediate clearance to land; which was granted; and I landed opposite direction on the departure runway without further incident; and taxied back to the ramp. Further ground runs produced similar roughness; though not as extreme; other run up parameters all checked out fine. After shutdown I talked to an A&P who had witnessed the event. He stated that we were leaving a visible black sooty exhaust trail. It then dawned on me that because the fuel and turbo system are set up at a specific (normal operating) oil pressure; the still thick; cold oil had probably affected the fuel delivery; and caused an extreme over-rich condition; in which the turbo controller was not keeping up with the fuel delivery. Further discussions with Maintenance personnel and another more experienced 206 pilot confirmed this as a likely cause. The next day; which was much warmer; my crew and I arrived at the airport later; when the temperature had already reached 55 degrees F. After a normal engine run-up and check; I did two full power ground runs; during which the engine performed normally. We then departed and completed the previous day's photo mission without further incident. The moral of the story is proper oil pressure is important on this aircraft; not just temperature. Also; on very cold mornings; it would be advisable to do a full power check on the ground; and adjust the mixture as necessary to avoid an over-rich condition on departure. Even better would be to give the aircraft a proper forced air preheat; or take other measures to ensure the entire engine compartment and all external oil lines do not get cold soaked at below freezing temperatures.
C206 pilot experiences a rough running engine just after takeoff on a very cold day and elects to return and land opposite direction on the departure runway. Post flight discussions with an A&P Mechanic reveal that high oil pressure may have produced the anomaly. The aircraft operates normally the next day.