Always Learning: Trees, 12 o’clock

Last summer, I made a mistake that led to another lesson learned.

My son and I awoke in our dew-covered tent at the Antique Airplane Association’s annual fly-in at Antique Airfield (IA27) in Blakesburg, Iowa. While packing for our early morning flight home, a check of the weather confirmed a narrow temperature-dew point spread with visible moisture in the air—ideal conditions for carburetor ice to form in my Cessna 140’s small Continental C-85 engine.

After starting the engine I applied full carb heat. The pilot’s operating handbook advises: “Carburetor ice can form on the ground with the engine idling, therefore be sure and have the carburetor heat in the On position. Leave it in that position until you open the throttle for the takeoff run. Then move carburetor heat to the cold air position. This gives maximum power for the takeoff. Then watch engine for any indications of ice (roughness or loss of rpm) during climb and apply full carburetor heat if engine begins to ice.”

Engine runup and checklists complete, I did a final flow pattern check of all instruments, gauges, and controls—confirming carb heat was still on—before taxiing to the runway. Density altitude would be a factor on this hot, humid morning, and I wanted to be certain to have full power available for takeoff from this short grass runway with tall trees 600 feet beyond the departure end. I briefed my son on our course of action if we experienced carb ice on takeoff; we would avoid the trees that lay directly ahead by turning right and flying through a narrow valley.

The Antique Aircraft Association uses nonstandard procedures during its fly-in. There are no radio calls in the traffic pattern, as many airplanes do not have electrical systems. Every operation is strictly see and avoid, with one exception: Takeoffs and landings are controlled by flaggers standing at the approach end of the runway, who wave a green flag to clear aircraft for landings and takeoffs and a red flag to indicate a go-around or hold short.

As I approached the departure end of the runway, the green flag was briskly waved at me in a manner that indicated “immediate departure.” Without delay I accelerated down the undulating grass runway. Our wheels broke ground about when I expected, but our airspeed was not increasing as quickly as normal. The trees were growing larger.

When faced with an obstruction at the end of a short runway, there is a powerful urge to climb immediately to clear the obstruction as soon as possible—but that can lead to a decay in airspeed and significant reduction in climb performance. Accelerating to best angle of climb airspeed (V_X) while still in ground effect and climbing as soon as you attain V_X is the best course of action. Thanks to good training, I followed this procedure—but as we approached the trees, I could see we would not clear them. I banked right as briefed, buying time to figure out why our climb rate was so anemic. A quick scan of the instrument panel immediately revealed the problem—carb heat was still fully applied, reducing engine rpm and degrading climb performance. I pushed the carb heat off and the airplane quickly ascended above the trees. I apologized to my son for the uncomfortably close view of the treetops, and we headed for home.  

I let myself get distracted by the unique fly-in procedures and forgot to turn the carb heat off while applying full throttle on the takeoff roll. The best way to avoid distraction is to slow down, be deliberate, and use flow patterns and checklists. Since this unwanted adventure, I always turn the carb heat off during my final flow pattern check before entering the runway—and I haven’t repeated the mistake. On the positive side, the pretakeoff briefing really paid off. I just didn’t expect that my tree-avoidance plan would have to bail me out of my own blunder.