Wednesday, November 19, 2008

Emergency...?

Date Aircraft Route of Flight Time (hrs) Total (hrs)
19 Nov 2008 N21481 5G0 (Le Roy, NY) - GVQ (Batavia, NY) - 5G0 0.8 673.4

With the ambient air at thirty-three degrees Fahrenheit, a thin blanket of melting snow began to retreat, revealing runway asphalt beneath. A fortuitous break in the weather provided opportunity to launch from Le Roy on a brief ferry flight to nearby Batavia for maintenance. Since installing an engine analyzer in N21481 a few months previous, I was concerned that my #3 cylinder routinely ran hot, easily recording cylinder head temperatures (CHT) at the 400°F mark that most experts cite as unhealthy.

I pushed the throttle full forward and Warrior 481 trundled along the wet runway. As the airplane climbed into the cool air, I noticed some runway slush spattered on the leading edge of the wing. I continued to climb away from Le Roy on runway heading. As I reached 1500 feet, I noticed that the #3 cylinder already registered 400°F. I pushed the nose forward to improve the flow of cooling air over the engine.

For an overcast day, it was surprisingly turbulent. At 2000 feet, I corrected for a couple of significant bumps when I felt a loss of power. The airplane suddenly bucked and the engine sputtered. I saw the tachometer drop to 2000 RPM and I pulled the carburetor heat lever without really even thinking about it. That is what training in a carburetor icing-prone Cessna 150 will do for you. Not that I seriously believed carburetor icing to be the culprit - Cherokees are notoriously resistant to carburetor icing and I never experienced it during five years of all-season flying in Warrior 481. The engine continued to run rough and I saw the exhaust temperature on cylinder #3 suddenly spike. This is it, I thought. I ran that cylinder too hot too long and now I'm losing it.

I brought the throttle back to idle to get the cylinder temperatures down and wheeled the airplane into a 180° turn back to the Le Roy airport. Trimmed for a 74 knot best glide speed, I announced an emergency landing and easily managed to glide through the pattern and land; my first precautionary landing in eight years of flying.

I advanced the throttle slightly to taxi clear of the runway and switched the carburetor heating off. Once I found a dry parcel of taxiway, I locked the brakes and ran the engine up to full power. RPM came up as it normally does and the engine analyzer showed all cylinder temperatures rising evenly. Confounded, I swept my gaze across an instrument panel displaying nothing but nominal readings. It was as though the airplane was saying, "why so uptight? Everything's normal here."

Carburetor icing is the only explanation. Conditions must have been just right; air temperatures near freezing with lots of moisture available from the wet runway. Perhaps some of the slush I saw on the leading edge of the wing also made it into the air intake such that every breath taken by Warrior 481 was saturated with moisture. But I will never really know for sure. The problem with carburetor icing is that all evidence of the problem literally melts away.  I experienced carburetor icing several times in a Cessna 150, most notably on the day of my first solo and the day I took my mother for her first airplane ride.  But those were benign events compared to the convulsions my Warrior's Lycoming O-320 experienced that day.  In fact, the instance with my mother was so mild that I remedied the situation without her ever realizing anything was amiss.

My heart rate settled a bit as I came to accept that my first real emergency…wasn't.

Fortunately, the constant threat of carburetor icing during my student pilot days made application of carburetor heat automatic at the slightest hint of power loss. Had I not used the carburetor heat, ice may have completely choked off the flow of air and fuel to the engine and I would have had a real emergency on my hands.

I taxied to the departure end of the runway and performed another flawless full power run-up. Satisfied, I departed the wet runway a second time and circled the airport. The engine ran normally and, once I was certain that it would continue to do so, I flew to Batavia.

After some time spent with my mechanic, we repaired the loose metal baffle between cylinders #1 and #3 and improved the sealing of some of the other baffles. My engine was free of typical visual indicators of damaging heat and my mechanic surmised that, though cylinder #3 had been running hot, it had probably not been so hot as to cause any catastrophic problems. Nevertheless, I was delighted to see all four cylinder head temperatures within three degrees of each other as I climbed away from Batavia that afternoon. It was time well spent: I fixed my airplane AND joined the somewhat select ranks of pilots to experience carburetor icing in a Cherokee.

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