It had been a long, busy day for my Piper Arrow and me one April evening several years ago. Our early morning flight from Iowa City to Minneapolis terminated in a "max forward speed to the marker" ILS approach. After a long day of meetings and a 20-minute taxi delay behind a queue of departing jets, I finally began to head home in instrument meteorological conditions (IMC) after dark.
Established in cruise at 10,000 feet, the outside air temperature (OAT) was hovering right around freezing; periodic flashlight checks revealed no trace of icing, and occasional shots of landing light revealed rather large snowflakes streaming toward the windscreen. I kept the pitot heat on continually, even though Flight Watch had no pilot reports or forecasts of icing. Iowa City had no weather reporting in those days, but my alternate, Cedar Rapids (15 miles northwest), was reporting a 600-foot ceiling and two miles’ visibility—despite the fact that the forecast and reports were well above alternate minimum requirements at the time of my departure.
Knowing that Iowa City’s weather is generally a bit better than that in Cedar Rapids, and that I could always return to Cedar Rapids and shoot the ILS there if necessary, I accepted a descent and vectors for the VOR approach at Iowa City.
During the descent, the OAT remained right at freezing all the way from my cruising altitude down to the initial vectoring altitude of 3,000 feet. The appendages remained ice-free during the descent, and I was continually in rather heavy wet snow, with no ground contact. But the Arrow and I had spent many hours together in IMC at night, and it was smooth and warm in my little cocoon, so I prepared for the approach and a possible diversion to Cedar Rapids on the missed.
As Cedar Rapids Approach cleared me to 2,500 feet and assigned a vector to the final approach course, the engine gently and smoothly wound down to silence. I couldn’t believe it. I was just a couple of thousand feet above the ground in IMC on a dark night, 10 miles from the nearest airport, with no engine. I informed Approach that I had lost power as I simultaneously tried everything to get the engine to run again. The prop was still turning, as if the engine were developing idle power. The controller gave me an immediate turn to Iowa City, asked for souls on board, and told me that he had contacted the sheriff for possible ground rescue. At that moment, an anonymous voice on the frequency said, "alternate air." I again pulled the alternate air handle and left it open, still with no immediate effect.
As I was descending through about 1,000 feet agl, still in IMC with no ground contact, the engine suddenly roared to life with full power. I informed Approach, which asked if I wished to continue direct to the airport at the minimum descent altitude of about 1,300 feet msl. (I was in the general vicinity of the published final approach course over flat terrain with no obstacles.) I accepted, broke out to fuzzy ground contact at 1,500 feet msl, got the airport in sight about a half-mile out, and successfully landed with the engine acting quite normally, even with the manual alternate air control off while taxiing.
The next morning, we pulled the Arrow into the shop and found that the sponge-type induction air filter, which is mounted at the left rear of the engine compartment, was saturated with water. We literally wrung it out, reinstalled it, and made a test flight with no abnormalities noted. The following day, I made another trip to Minneapolis and back (all VMC) with a completely normal engine.
This incident taught both mechanical and operational lessons. I theorized that during the 90-minute flight, moisture entered the induction air intake and was absorbed by the sponge filter. Eventually the filter got so clogged, and/or the saturated material started to freeze, that the induction air supply became blocked. The Arrow’s spring-loaded alternate-air door is designed to be sucked open in such circumstances. But in the near-freezing conditions, it likely was frozen to its frame and could not open automatically. My initial cycling of the cable-driven manual control was not sufficient to break the ice. A few moments later, when I activated the control and left it open, the ice finally broke, allowing the door to open and the engine to develop normal power. The mechanical lesson learned is that in near-freezing conditions, one should cycle the alternate air frequently to be sure that the door is free, since the induction suction may not be sufficient to open it. I believe this explains a mysterious experience I’d had a few years earlier, with two occurrences of slight loss of power, then surging recovery a few moments later, during cruise in continuous light snow.
Once the engine redeveloped normal power, it was foolish of me to continue my headlong low-altitude rush to a circling approach at minimums at Iowa City. Knowing that conditions were near minimum there on a dark snowy night and that I had a possibly sick engine, I should have requested a climb and diversion to the sure-thing ILS at nearby Cedar Rapids. Had the engine problem recurred, I would at least have bought myself some altitude and proximity to a much safer approach under the conditions.
Forrest M. Holly Jr., AOPA 528540 , is a professor at the University of Iowa. He holds a commercial certificate with an instrument rating and currently flies a 1975 Beech F33A Bonanza.
"Never Again" is presented to enhance safety by providing a forum for pilots to learn from the experiences of others. Manuscripts should be typewritten, double-spaced, and sent to: Editor, AOPA Pilot , 421 Aviation Way, Frederick, Maryland 21701.
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