Problem solving via systems knowledge

Suddenly, a blinking red light on the instrument panel catches your eye—you have a problem. Should you divert to the nearest airport or return to your departure airport? Should you land at once or ignore it and continue to your destination?

What’s that? You need to know something more about the red light to make the right choice? Might you need an understanding of the system the light is part of to problem-solve this potentially day-ruining blinker?

This is why systems knowledge is part of flight training. It’s the tool kit for problem-solving.

Fuel systems

Of all the systems on the airplane that your actions can affect most, the fuel system is at the top of the list. You’d be shocked by how many off-airport fuel starvation accidents there are each year in which a pilot puts down with one full tank and one empty tank under the impression that all fuel had been expended.

There are nearly as many different fuel systems as there are different airplanes. Broadly speaking, there are gravity-feed systems and there are fuel-pump supply systems—but the devil’s in the details. Vents, sumps, lines, cutoffs, and tank selectors for multiple tanks all vary. The key point is to understand how a fuel molecule gets from the bottom of the fuel truck to the top of one of the cylinders in your engine.

A failure of the fuel delivery system results in a sputtering engine that quickly goes silent. Assuming you have fuel, your knowledge of potential roadblocks can assure you’ll clear them should they arise. Check and cycle the fuel tank selector or selectors. This ensures that if somehow one of your fuel shutoff controls has closed, it’s now open. Do you have maintenance shutoffs for the fuel lines on the side walls or under the panel? If so, check those by opening and closing them. And if contamination is blocking the line, there’s a chance that opening and closing each may dislodge it, or, depending on the fuel system, may allow you to bypass the blockage and deliver fuel from a different tank.

Induction systems

The induction system is how air is introduced into the combustion cycle. It provides a path for the transport of air, mixes that air with fuel, and delivers the mixture to the cylinders. Pretty much all induction systems draw air from the front of the cowl, typically through an air filter. As the filter might become clogged by debris or blocked by ice, many airplanes have an alternate air supply, usually drawing from the inside of the cowl, that are automatic or pilot-deployed.

The induction system also includes either a carburetor or fuel injection system, either of which can create different problems on both the ground and in the air. On the ground, the starting procedures vary. In the air, carburetors are subject to carb ice at a wide variety of temperature, dew point, humidity, and power combinations—so most are equipped with a source of hot air from the engine compartment that can melt off the ice called carb heat. This control can also be used to prevent carburetor icing in conditions where it is likely—such as throttling back to land on a humid day, even when it is quite warm. The design of the carburetor can lower the temperature of the fuel-air mixture by 70 degrees Fahrenheit.

Carb ice builds up in the venturi, the skinny part of the carburetor where the throttle butterfly valve lives. The initial buildup is generally slow, so the first warning sign is a small reduction in rpm like what you’d get from a small reduction in throttle. In fact, that’s what you are effectively getting. Just like pulling back on the throttle causes the butterfly valve to reduce the flow through the venturi, so too, does ice build-up.

As the ice builds, rpm continue to drop off. If the ice gets bad, the engine will start running rough and eventually can be choked off completely and stop in flight. To avoid this, get the carb heat on as soon as carb ice is suspected—basically any unexpected rpm drop—even before checking the other possible rpm theft suspects. This should be your first action for two reasons. First, there is no harm in having carb heat on for a time, even if it didn’t turn out to be needed. Second, if there is ice, clearing it takes time. Picture holding a hair dryer to an ice cube.

Leave the carb heat on while you troubleshoot. Check the throttle response. A loose throttle friction lock can cause an rpm loss, as can a vibration-induced mixture change. So too, can a magneto failure, which you can rule out with an in-flight mag check. More rarely, contaminated fuel can trigger an rpm drop, so switch tanks. There are many possible causes of an rpm drop, but carb ice is both the most likely and the issue that takes the longest to fix. In some airplanes, engaging carb heat causes yet more of an rpm drop, which leads some pilots to reverse their action, letting the ice start to build again.

Like the fuel system, having a mental picture of how air travels through the induction system is essential to diagnosing combustion issues.

Powerplants

Knowing the brand, horsepower, and the rest of the commonly taught rote knowledge on engines doesn’t help in problem-solving engine issues. Instead, know that engines only need three things to run: fuel, air, and spark. If your engine isn’t running well, or stops altogether, those are the things you need to check.

The final delivery mechanisms of the fuel system are the throttle and mixture controls. These are crucial elements of the system when it comes to troubleshooting. Power spool back? It could be as simple as a loose friction lock on the throttle. Engine running rough? Maybe the mixture is set too lean for your altitude. The two levers are possible points of failure in the smooth delivery of fuel from the tanks to the engine.

Now let’s look at spark. At first you might think you have little power over this aspect of the powerplant, but you do have one control: the ignition switch. If the engine acts up, ensure the magnetos are set to Both, unless the engine is shaking like a wet dog—this could be a sign of a mag misfiring, and you can quickly isolate the bad one and shut it down using that “right-left-both” control.

There are times, although rare, when engines mechanically fail. You might recall being told that your engine is “direct drive,” meaning the propeller is bolted directly onto the crankshaft with no transmission. In flight, if an engine fails, the prop will windmill in the relative wind, so long as the crankshaft can turn. In a GA airplane with a fixed-pitch propeller, if the prop stops moving in flight, something terrible has happened—mechanically—to keep the crankshaft from moving. That’s not a fuel-air-spark problem and it’s time to choose an emergency landing spot.

A solid understanding of the powerplant cooling system is also worthwhile. Most of our engines are air-cooled, with the cowl dividing the engine compartment into two halves. The system is set up so that the top half is slightly higher pressure and air flows uniformly down the cylinder fins to the bottom of the compartment. If you are seeing an increase in engine temperatures, check the baffling for holes or damage. An air-cooled engine also gets a lot of its cooling from the circulation of oil, so oil temperature, oil pressure, and cylinder head temperatures tend to correlate and can serve as cross checks on each other. Steadily dropping oil pressure with rising oil and engine temperatures could suggest an oil leak, and that demands a quick landing

Electrifying knowledge

The number one thing you need to understand about the electrical system as a pilot is that you don’t need it. The airplane will fly just fine if it fails.

So, then, what does the electrical system do? It powers your com radios, nav radios, the intercom, and your transponder as well as your lighting system. In some airplanes the wing flaps are electric. Likewise, some trim systems are electric. If you have a “switch on” backup fuel pump, it’s probably electrical too. The list goes on: pitot heat and some deicing and anti-icing equipment; autopilot and landing gear (if equipped); and depending on your aircraft, your flight instruments may be electric. Of course, all glass-panel avionics are electrical. In a traditional analog setup, it’s possible that all three gyroscopic flight instruments—the attitude indicator, heading indicator, and turn coordinator—are powered electrically.

That’s a lot of powered stuff that will start sucking your battery dry the second after an alternator/generator failure. The trick in such a case is immediately prioritizing what you need and shutting down everything else to preserve battery life. If you are VFR on a lovely day and know where you are, shut it all down and fly the airplane. When you get close to the airport you were heading to, power up your radios and any other items you need to land safely.

In the case of an electrical fire, an understanding of how your electrical system is divided and segmented can help you isolate the affected circuit. Think about the journey of the electron in a similar way to the journey of our fuel molecule. How does your ship make electricity and how does it use and store it?

Any airplane that has an electrical system has at least one battery. That’s where the commonalities end. Older airplanes have generators to make electricity, and they don’t put out much power at low rpm. Also, the generator systems tend to directly feed the battery, while the battery itself directly powers the airplane. If the airplane sucks more power out of the battery than the generator is producing, things will shut down. In newer alternator-powered airplanes, the alternator most often powers the ship directly while topping off the battery as a side job. In this kind of setup, the battery really only comes into play for starting and for emergency power if the alternator fails. Such airplanes commonly feature a split master switch, allowing the pilot to shunt the power supply from the alternator to the battery.

The electrical delivery system involves switches, buses, and circuit breakers or, in older airplanes, fuses. Working backward, circuit breakers provide overload protection for individual circuits. In some airplanes there are lots of circuit breakers, seemingly one for each electrical device in the airplane, in other airplanes only a few. It’s handy to have an understanding of which electrical appliances are plugged into the various circuits. Buses are like power strips and can be used to create primary and secondary power systems. Switches can let you further isolate individual components or systems and are also handy for shutting down less-critical devices in an alternator or generator failure to maximize battery life. The older the batteries are, the less charge they hold. Don’t expect to get whatever number of minutes the manual says you’ll get unless you just got a new battery.

The health of your alternator or generator can be monitored in multiple ways, depending on how your airplane is equipped. Many have a warning light on the panel—include that light in your normal scan. In a glass cockpit airplane with digital instruments, you will likely get a caution or warning message. For the rest of the pack, your go-to indicators are a variety of electrical monitoring instruments. Broadly speaking, they fall into three categories: voltmeters, ammeters, and loadmeters.

Voltmeters show the output of the alternator or generator in volts. No volts, no alternator or generator action. The electrical system in the airplane will likely have either a circuit breaker or a fuse, and once you note that your power generation is offline you should check, reset, or replace as necessary. In airplanes with split master switches make sure the alternator half of the switch didn’t somehow get turned off.

Next, the ammeter, which often confuses students. This is a battery health indicator, showing if the battery is charging or discharging. In flight, the alternator/generator should always be charging the battery. But if the alternator/generator goes offline, the battery will step in to pick up the slack and begin discharging, and this will show on the ammeter. In the most common type, the 12 o’clock reading on the dial’s face is a zero with negative numbers to the left, and positive numbers to the right. If the pointer is in positive territory, power is flowing from the alternator/generator to the battery and the battery is charging. If the indicator shows a negative number, a few different things could be happening. The battery is sending out more power than it is receiving, so the airplane is using more power than the alternator/generator is producing. This is common in generator systems at low rpm, during, say, taxi, and doesn’t necessarily mean the generator has failed. That said, with this instrument, a full-scale deflection to the negative shows the alternator/generator has kicked the bucket.

Then there’s the loadmeter gauge with zero amps to the left and a higher number to the right. This is sort of a capacity instrument, showing what percentage of the power generation is being used, expressed in amps. As such, a drop to zero, or near zero—when electrical devices are in use during flight—is an indication that the alternator/generator isn’t alternating/generating.

Regardless of how you’re equipped, you need to understand how to read what your instruments are telling you so that, if problems develop, you’ll be aware of it at the soonest opportunity.

Problem-solving with knowledge

We learn systems so we can understand what’s happening when things go wrong. When the red light blinks on the panel we’ll know if we can fix it in flight, shrug our shoulders and fly on, or if we need to land immediately. Systems knowledge isn’t for the sake of knowledge. It’s the premiere in-flight problem-solving tool. FT

William E. Dubois is the ground school program manager for Infinity Flight Group. He is a master ground instructor accredited by NAFI and MICEP.