Questions from the Cockpit: Not your father’s electrical system

As I made my way across the hangar to my office, one of the airline cadets stopped me and made a seemingly simple request. A “simple” request that ended up consuming endless hours of research and prep and revealed to me just how much aviation has changed over the last decade or so.

The request was, “Can we take a deep dive into the electrical system on our next group grounds?”

Not knowing what I was getting myself into, and thinking that this was a pretty shallow pond to take a deep dive into, I said, “Sure no problem, I’ll pull together something for next week,” while in the back of my mind wondering how I’d fill the rest of the hour-long ground session.

But… well… do you remember those Oldsmobile commercials from a while back? When the car maker was trying to shake its brand-for-old-fogies reputation? It’s not your father’s Oldsmobile. Yeah. As it turns out, the exact same can be said of airplane electrical systems. They’ve changed. A lot.

Not only did I not have time left over, but the deep dive ate up four full sessions. No fear, we won’t be diving that deeply today.

But it is interesting how electrical systems have changed over the 100-plus years of flight, and especially in recent times. It’s something for traditionally-trained pilots to think about when stepping into newer airplanes, because even today’s Cessna 172, well, it isn’t your father’s Cessna 172.

Back in the day, airplane electrical systems were super simple. They didn’t have one. It doesn’t get any simpler than that. Imagine the oral exam, “Applicant, tell me about your airplane’s electrical system.”

Applicant: “It doesn’t have one.”

Examiner: “Excellent, that finishes the oral exam, let’s go fly.”

(For my non-pilot readers, most airplane engines generate power for their spark plugs using magnetos, but that’s not considered an electrical “system.”)

Fast forward a few decades, and now we have modern conveniences that need electricity. Things like radios and lights. The first generation solution was a generator-battery system, and they aren’t too hard to understand. Typically, these airplanes also have an electric starter that gets the engine spinning so that it will start, and this starter gets its juice from a battery. Commonly, the battery also supplies all the power to the ship.

Of course, even simple radios and lights would make short work of a battery, so that’s where the generator comes in. Once the engine is running, it, in turn, spins a generator which “generates” electricity to recharge the battery.

There’s not a lot to the system: There are some switches, a fuse or two, and a dial to let you see if your generator is providing more power to the battery than the ship is draining away from it.

Although more complex than “it doesn’t have one,” the systems were very simple and straightforward. You could draw one out on a cocktail napkin, and easily explain it to third graders. We still have airplanes out there today flying with generator-battery systems.

But, technology marches forward, doesn’t it? It wasn’t long before there were new and exciting things that pilots yearned for in their airplanes. Electrical flight instruments. Improved navigation systems. Autopilots. And the generator-battery systems had a hard time keeping up with the changing demands of technology.

Among other problems, the electrical output of a generator is directly linked to how fast it spins. Said aeronautically, they don’t generate much power during taxi, and a power-hungry airplane might drain the battery on a long taxi, and there you were at the hold-short line with no radio and your nav system off line.

So the next generation of electrical systems saw generators replaced by an alternator, a device that can produce full power even at low speeds. Of course, as the name suggests, an alternator produces alternating current, and airplanes use direct current, so the juice needs to be converted, making the system a little more complex.

Alternator systems also tend to be set up a bit differently, moving the battery to a startup and standby role; with the alternator supplying the ship with power directly, and recharging the battery as a side gig.

But if something bad happens to the alternator (something bad is always happening to alternators, by the way) the system is wired such that the battery can step in and run everything just like it did back in the generator days. At least for a short time. The wise pilot shuts down anything he or she didn’t absolutely need to make the battery last as long as possible when something bad inevitably happens to the alternator.

But again, the system wasn’t that complicated. Maybe we need a Big Chief writing tablet rather than a cocktail napkin, and we might lose the third graders, but the fifth graders can follow us.

Then glass happened. And glass is run by computers. More than one computer, generally. Now the Cessna 172 needs more power than an entire house did in 1972.

Most modern GA airplanes with glass avionics have at least two batteries for the airplane, and some instruments within the airplane have their own independent batteries. Some modern airplanes have more than one alternator. All have multiple “buses,” connection points for devices that dictate power routing. Fuses are largely gone, replaced with circuit breakers. Many times lots of circuit breakers.

With this escalating complexity comes more points of possible failure, so the systems have to have levels of redundancy so that if something fails, the whole thing won’t collapse like a house of cards.

The diagrams of modern electrical systems — the one for the C172S takes three pages — look like something from a college class in electrical engineering. The fifth graders are now lost and have abandoned you to join the third graders on the playground.

As have three-quarter of the adult pilots in the room.

The cadet was right. This takes a deep dive. The electrical system, once so simple a child could grasp it, has become mind-bogglingly complex. But flying a modern airplane without truly understanding its electrical system is akin to flying cross-country without checking the weather. Sure, you can do it. But only if you get lucky.

So how do you go about learning college electrical when you trained in third grade?

Start with the POH’s schematic of the electrical system, which, granted, can be hard to interpret, but just realize that it is a map of what connects to what inside of your airplane.

The schematics use specialized symbols, much the way a navigational chart has specialized symbols, so — just like when you learned to read a sectional chart — you need a legend. A good one is found in the Aviation Maintenance Technician Handbook – General, FAA H-8083-30B, which you can download from the agency’s website. Page 4-24 has most of the common symbols.

With the schematic and the legend, you have the tools to figure it out, but to help you really “get” how it works — without giving yourself a stroke from concentration — I highly recommend that you Google “UND Interactive Trainers.”

The University of North Dakota, which has a strong collegiate flight program, has been good enough to make some of its online educational resources available to everyone. (Thank you UND! Go Fighting Hawks! Whoot, whoot!)

One type, the UND electrical system trainers, are basically POH diagrams brought to life. You can turn the engine on and off, shut down various systems and subsystems, flip switches, and pull breakers — all on your computer — and every time you do, the diagram shifts color to show you what kind of power is flowing, and to where. There are also little popup text boxes to tell you more about various components. It’s frickin’ brilliant.

Even if you aren’t flying one of the three types of airplanes for which they have trainers (the Cessna 172S, and Piper’s Archer and Seminole), spending a little time with these trainers is a good way to get a fundamental grasp on what your electrical diagram is trying to show you.

When you can see it in action on one diagram, it doesn’t take much imagination to translate that information onto another diagram. And I’m speaking from experience here. After diving deep into the Cessna 172 for group grounds, I was reviewing the diagram in a POH for an altogether different airplane I’m getting checked out in, and the schematic “came to life” for me quickly in my mind’s eye.

Now, what I was trying to grasp in understanding this electrical schematic, and what all pilots of today’s Oldsmobiles need to understand, is simply this: What will still work, and what won’t work anymore in various modes of failure. And for that, you need to understand how the power flows, and its various divergent streams.

Some electrical devices can draw power from more than one source, others, cannot.

For instance, many modern airplanes have electric flaps and electric trim. But where are those things plugged in? If you are down to your backup battery, will you still have flaps or your trim? Good to know.

It just takes a little more time to learn the systems nowadays. Because, over time, the electrical pond has become a deep lake.

But don’t be afraid to dive in. The water’s fine.