Sudden changes merit prompt scrutiny
But when we convened in the cockpit one sunny-with-clouds morning, the Flying Carpet wouldn't start-it cranked without firing. How embarrassing, with my new-pilot passenger on board. Fuel dripping from the cowl suggested that I'd flooded the engine, but clearing the carburetor with lean mixture didn't work.
Discouraged, I was at least smart enough to quit cranking before running the battery down. Not long before, another new aviator had phoned me, distraught. In trying to restart his airplane's engine at Lake Havasu City, Arizona, Dan, a student pilot, had drained the battery. By the time it was removed for recharging, nightfall was approaching. His pride crushed, Dan had rented a car and driven four hours home.
Determined not to repeat Dan's mistake, I quit when the starter slowed and called a mechanic to jump the battery. Even then the engine was slow to fire, but once started it ran flawlessly. I confirmed with the mechanic that fuel no longer dripped after starting, and that no further action was required. Then we took off.
We soon found ourselves topping scattered clouds at 8,500 feet, uncommon in a place where skies are usually either clear or too foul for lightplane flying. "Is it OK for us to be here, Jon?" I asked, playing instructor now that my self-respect had returned. "I don't see why not," he said, noting clear skies behind us, holes all around, and forecast improvement. "Most important," he observed, "I'm traveling with an IFR airplane and pilot." I'd just pulled out my approach plates when Sedona materialized beneath a large hole. Applying flaps, we plummeted down to enter the traffic pattern.
Over lunch at the airport restaurant, Jon and I watched blue sky battle ivory clouds for the privilege of crowning red rock pinnacles. By the time we hiked to the scenic overlook and back, sunshine had triumphed. This time the engine roared quickly to life; Jon and I returned to Phoenix bearing new stories and new friendship.
I phoned Dan that afternoon to say, "See, hard starting can happen to anyone." Still, I was troubled. Had the problem truly been caused by poor technique? Or would it plague me again? I couldn't imagine what I'd have done differently to avoid it.
The next day I repositioned the plane for a photo shoot. This time the engine started more readily, but the hour was later and the day warmer. Did it still take longer than usual to start? I wondered.
With a business trip coming up, I didn't want to take chances. So I phoned Herb, my shop's maintenance coordinator, wondering whether the plane merited examination. "Keep an eye on it over the next few starts," he said, "and let me know if the problem persists." But when I mentioned that this was my first such difficulty in years, Herb changed his tune.
"So that plane has consistently started easily for you?"
"Yeah, always within two turns of the prop."
"Whenever you experience a sudden change in airplane operation, it's wise to have a look. Tell me again what happened, in detail." We brainstormed through the problem.
"The engine cranked quickly but wouldn't fire at all. So I looked under the nose to see if it was flooded. Sure enough, fuel had puddled there. Even using the power cart the engine took a while to start. It caught and quit several times, then ran fine."
"How much prime did you give it, Greg?"
"Just two shots. That's why I was surprised when it flooded."
"Did you pump the throttle?"
"No."
"Flooding more commonly occurs from pumping the throttle than from overpriming. Any trouble starting the engine for the return trip?"
"Nope, it fired right up."
"And the next day, when you repositioned it?"
"The air was warmer so I applied just half a shot of prime. Even then it seemed to crank longer than usual before catching. But maybe I underprimed after the previous experience."
Herb thought for a moment. "Just an idea, Greg, but I wonder if you have a leaky primer line. If so, it would spray fuel into the engine compartment instead of the engine itself. Obviously that could be dangerous, so let's have a look." Herb's hypothesis immediately struck a chord. The smooth-running engine and easy starts on each return trip suggested healthy fuel lines and proper carburetor operation. But no wonder the engine wouldn't fire when cold if priming fuel wasn't entering the cylinders.
Shortly afterward, Herb phoned with his diagnosis. On this engine, the primer system divides at the firewall into two lines, each feeding the intake manifold for one side of the engine. Not only was one line broken, but the other was plugged. Other puzzle pieces now fell into place-like why in the past the engine had sometimes run rough after cold starts. With one line plugged, half the engine had been receiving no prime; once the other side broke it received none at all, which is why I couldn't start it.
Funny how such observations often don't sink in until prompted by other information. Under the seemingly flooded engine, I'd been surprised to find the fuel puddle not directly under the carburetor. When I'd first mentioned that to Herb, he'd commented that fuel often travels within the cowl before dripping out. Now I knew that the puddle had come from the broken primer line, not the carburetor. I had missed subtle but important cues, and I vowed it wouldn't happen again.
I phoned Jon and Dan to share the lesson. Sometimes there's more to an embarrassing situation than first meets the eye-happily, I'd dug deeper before writing off the hard start as pilot error. But I should have acted sooner. Although not nearly so dangerous as a broken fuel line, which supplies fuel continuously whenever the engine is running, every prestart primer stroke was spraying gasoline into the engine compartment. Left unchecked, that might have caught up with me one day.
Never having experienced such a problem before, I might legitimately plead ignorance for not recognizing it. Now I know the symptoms of a broken primer line. But we pilots dare not tempt fate by learning all our lessons through hard knocks. Whenever a plane's operation or performance changes, it's wise to call in the pros for a look. Thanks, Herb, for spelling that out.
Greg Brown was the 2000 National Flight Instructor of the Year. His books include Flying Carpet: The Soul of an Airplane, The Savvy Flight Instructor, The Turbine Pilot's Flight Manual, and Job Hunting for Pilots. Visit his Web site.
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