On Popping Circuit Breakers

I learn about a Raven II’s Fuel System While Troubleshooting a Pesky Circuit Breaker

Starting a Raven II is a weird process. You turn on the master battery switch, push the mixture full rich, then turn the key to prime and count 5. Behind you, you can hear the sound of the auxiliary fuel pump priming the engine. Then you position the key to Both, pull the mixture knob out to engine cutoff (full lean), and push a starter button. When you hear the engine catch, you push the mixture knob back in to full rich and put the guard over it. Throttle up to 50%-60% RPM, engage the clutch, the strobe, and the alternator. The blades start spinning within five seconds, usually with the sound of new drive belts slipping (at first) on the sheave. Then, as the belts tighten, the sounds all sound good and it’s a matter of waiting until the clutch light goes out before finishing the startup procedure.

The very first time I started Zero-Mike-Lima, at the Robinson factory last Thursday, the engine caught right away. That was easy, I remember thinking to myself. Since then, I’ve had mixed results. I just have to get the hang of it, I guess. First time was luck.

Zero-Mike-Lima has already shown me a potential problem. Nothing major, thankfully. When it’s cold out on start — like it was on the morning of day two of my ferry flight and again yesterday morning — the auxiliary fuel pump circuit breaker pops right after startup. Fortunately, I was still on the ground, so the first time, so I didn’t worry much about it. I just pulled out the Pilot’s Operating Handbook and consulted Section 4 for information about what to do if the Aux Fuel light comes on. It said that if the engine continued to operate normally, I should land as soon as practicable (as opposed to land as soon as possible). I was already landed, so that wasn’t a big deal. I pushed the circuit breaker in, the light went out, and I continued my startup process. It didn’t pop again and the light didn’t go on. A fluke, I decided the first time. The new helicopter is just shaking out a few little bugs.

On Friday evening, I pulled out my Maintenance Manual and looked up the fuel system. I soon became an expert (of sorts) in how the Raven II’s fuel system is designed. There are two fuel pumps: an engine-driven pump and an electric (aux) pump. Either pump provides more fuel to the engine than it will ever need. So the system is designed for redundancy. If the engine-driven pump dies, the aux pump, which is running whenever the engine is running, will take up the slack. The excess fuel that these pumps provide is pumped into the auxiliary fuel tank (the smaller of the two fuel tanks) which helps with fuel cooling.

I flew it on Saturday several times — starting it at least four times in the process — and the Aux Fuel problem never happened again. This further confirmed that the problem was a fluke. But yesterday, when I started it at about 10:00 AM, when it was only about 40°F outside, it did it again.

Time to call Robinson.

When I called the factory, I spoke to a guy named Ray who took the information about the problem and said he’d call back. He did — much later in the day — and left a voicemail message on my cell phone. He told me to look for pinched or shorted wires in the vicinity of the Aux Fuel Pump. He also told me to check the anemometer (gee, I hope I spelled that right) while starting up to see if there’s a power fluctuation before the breaker pops. So today I’ll have Ed look things over back there. Hopefully, it’s just a bad wire. But it could be a bad fuel pump, one that needs too much power to go to work on a cold day. I’ll keep an eye on the situation to see. I certainly won’t fly with that light on.

Of course, I did start it three times yesterday and the problem only occurred on the first start. So it definitely has to do with things being cold. That’s what I think, anyway.

But then again, what do I know? I’m just a pilot.

What do you think?