Failure is Not an Option -- Part I

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Failure of a key component of your plane like a vacuum pump or the electrical system is not optional -- it's a certainty if you fly enough hours. But failure to complete a flight safely after an electrical failure shouldn't be left to chance. A successful outcome is likely if you plan in advance.

Airmanship

The title of this article, which was made famous by Gene Kranz during the Apollo 13 mission, popped into my head recently while I was climbing my ham radio tower. Whenever I unhook my climbing safety belt and start to climb down, I take a moment to focus and remember to have one hand securely on the tower at all times. It's so important to my life at that moment that I want to be focused on it.

When the alternator or the electrical system goes belly up, however, it may be harder to focus on what to do since there's more going on, and because the cause and effect of your actions or inactions may not be as clear. Let go while climbing a tower and the effect is clear -- you die. Fail to throw one or more switches after an alternator fails and the effect may be the same, though not immediately. I've flown for 30 years, and recently learned several important subtleties about electrical failures in the Cessna T210 I fly.

The Other Guy is You

First, I have to admit that I've read articles about flying for decades, and used to think that things always happened to the other guy. But the years have proven me wrong. First there was the vacuum pump failure in a 182 while VFR on top. Later I got get-home-itis and went plowing through a nasty storm to get home. Though I had read much about it, I hadn't considered the effect a crying four-year-old would have on my judgment. Then I lost a brand-new alternator when the output stud burned off -- it was apparently defective and shorted out to the case. More recently I lost several close friends in a terrible twin accident. If you still think things only happen to the other guy, see a therapist!

Losing the alternator scared me more than it should have at the time. I was probably spooked because my partners and I had recently acquired the 1980 T210, and I had noticed that occasionally the power would flicker enough to make the lights go out for a moment and reset my GPS. This warned me that there was an electrical problem brewing, but I hadn't figured out where it was. When the failure finally occurred, I was VFR and en route to a maintenance shop to get some other work done. I was probably 20 miles out and the choices were to land at the airport nearly below me, or continue on to the maintenance shop. I did the latter and it worked out fine.

Continual Learning is Key

I've learned a lot about my airplane by reading articles, talking to other owners and mechanics, and through a three-day course offered by the Cessna Pilot's Association. I've concluded that while the emergency checklist and Pilots Operating Handbook are a great place to start if you lose an alternator or the entire electrical system, there are many other subtleties that you'll want to consider and plan for before a failure occurs -- which will happen eventually.

Electrical System Architecture

Dual Master Switch

Let's dive into the details of the electrical system. Most systems have either a 12-volt or 28-volt lead-acid battery that powers the plane, though which you have doesn't matter for this discussion. If you have a dual master switch, one half of the switch (often labeled battery) controls a contactor (which is a high current switch) that allows power to flow from the battery to the electrical and avionics buses. When this half of the master switch is off, no power flows to the electrical buses. From the buses, electricity flows through individual circuit breakers and on to every electrical device in the plane. The part of the system described thus far is the only part left to keep your electricity flowing after an alternator failure.

An alternator or generator, driven by the engine, is used to provide a continual charge to the battery. The alternator is controlled by a voltage regulator (also called an "alternator control unit") to maintain the proper charging voltage to the battery. Again if you have a split master switch, the other half, labeled alternator, enables the voltage regulator, allowing it to send a current (called the field current) to the alternator's electromagnets, which allows it to generate power. When the alternator half of the master switch is off, the alternator can no longer send a charging current to the battery.

The field current to the alternator's electromagnets is on the order of 3 amps. This is handy to know if you're starting a plane when the battery is low or on a very cold day. Just leave the alternator half of the master off when you first start the plane, which will allow all available current to go to the starter motor. Don't forget to turn the alternator half of the switch on after you start, or you will be running off just the battery, and will soon have no electricity at all! Some people recommend that you always start a plane this way so that high starting currents aren't pulled through the alternator's diodes.

Electrical Schematic



The system is fairly simple. When flying, you have electricity to power all of your lights and electronics forever, until the alternator fails. Then you have electricity until the battery fails, which may be 15 minutes or less if you don't immediately turn off most of the items using power. Even when the battery fails, the engine will still run. But by then, you will want to either be in VFR conditions planning to land without radio communications, or already be safely on the ground.

Recognize Electrical Failures Early

Engine Monitor

The key to preventing an alternator failure from turning into an emergency is to recognize it quickly. If it's night, you might notice a sudden or perhaps slow dimming of the electrical panel lights. You might also notice the ammeter showing a discharge. Some planes have a light labeled either low voltage or high voltage, but both indicate the same thing. Most likely it indicates that the voltage regulator detected a high voltage condition and tripped the alternator offline leading to a low voltage, but it could also be that the alternator or alternator belt failed. If you have an engine monitor that monitors battery voltage, a downward trend in voltage is probably the result of an alternator failure. In our plane, we've set the JPI EDM-800 engine monitor so that the gauge starts to flash whenever the voltage falls below 27.5 volts. There are lots of clues to an electrical failure, and like a medical problem, you want to notice the first signs and take action promptly.

On rare occasions you might detect smoke, and this article doesn't address what to do then. Suffice it to say that my approach would be to shut off the master quickly, and land immediately if smoke persists. I'm not a big believer in flipping switches on and off in cruise to try to identify the source of the smoke. Shut it all off now and you'll have plenty of time to figure out the problem after you're safely on the ground.

Start With the Checklist

If you don't see or smell smoke, then consult your checklist regarding electrical failures. The checklist for my single-engine Cessna is fairly simple:

1) Master switch -- OFF (both sides)
2) Master switch -- ON.
3) Low voltage light -- OFF
If low voltage light illuminates again:
4) Flight -- terminate as soon as practical.
It goes on further if "Ammeter Shows Discharge":
1) Alternator -- OFF
2) Nonessential electrical equipment -- OFF
3) Flight -- terminate as soon as practical.

Cycle the Master Switch -- Once!

The first step is to turn off the master switch. If there's an electrical problem, this will remove power from virtually the entire system, and will almost certainly stop any electrical problems from festering further. Step 2, to turn the master switch back on, is really just a way to determine whether the problem you had was a momentary glitch. If it was just a glitch, then you can motor on contentedly. If, however, the low voltage light comes on again, then you know it's not just a momentary gremlin, and that you may have a more serious electrical problem. General practice is to reset the master only one time. If you were to reset it repeatedly, you would increase the risk of turning a minor electrical problem into a fire, which is a full-blown emergency.

Let's assume that the ammeter shows a discharge, confirming that the alternator is no longer charging the battery, and that you then turned off the alternator side of your master switch to isolate it from the system. Now the game is to maximize the length of time that your battery will last. This is a minor issue if you're VFR, but could turn into a deadly issue if you're IFR and the battery runs out while you're still in the clag. The length of time you'll have power depends upon the size of the battery (its rating in ampere-hours), the total amount of current being drawn by every electrical device in your plane, and how much time passed before you noticed that the system failed!

Maximize Battery Time as the Astronauts Do

Gene Kranz's Book

This was critical to bringing the Apollo 13 home safely after an explosion crippled it. Life depended upon maximizing the time the batteries would last, which in turn necessitated minimizing the electrical load by shutting down the command module. Later, astronaut Ken Mattingly, working in the command module simulator in Houston, ultimately found a sequence of switches that allowed them to fire up the command module with the extremely limited battery power they had left. It was during the management of these life-threatening issues that Flight Director Gene Kranz uttered the phrase "Failure is not an option." As an aside, I met Gene a few years ago and he's a great guy.

When my alternator failed and wouldn't reset, I left the alternator side of the master switch off, and began to shed the electrical load. Avionics are the most obvious things to turn off first, since they're right there blinking at you. I turned off the DME and the transponder, since they're sensitive to voltage drops and will probably stop working first anyway. The GPS and the second radio went off next. I was able to pull the breaker to get my Stormscope off, but couldn't turn off the JPI engine monitor, since it was connected to the avionics bus and I wanted to keep using one radio. In the future, I plan to change all the circuit breakers over to the kind that I can pull off in flight.

Get Creative about Turning Off Power

Beacon

I thought I did a good job, but have recently realized that I forgot a number of things that would have extended the battery even more. For example the tail beacon draws several amps, and I never thought to turn it off. If I were IFR, I'd probably turn out all lights (even at night), since it would cut the battery drain, and ATC should be keeping everyone out of my airspace anyway. If the pitot heat were on, I'd want that off unless it was absolutely necessary. I'd also want to make sure the ADF is off, since it's hidden on the other side of the panel out of view (yes, I know that sounds strange, but I often leave it on so that I need only throw a switch on the audio panel to listen to news or music).

Cessna Autopilot

There's another item that I didn't consider, and I was shocked to learn that it's a power hog. Many Cessnas have the 400B or 400IFCS autopilot, and one might think that using it would simplify things while contending with an electrical failure. Wrong! That sucker draws about 16 amps, which is probably more than any other item in the ship. Turning off that one item will have a major impact upon extending your battery life. You'll also need to turn the autopilot off if you have a vacuum failure, since it operates off of signals fed from the attitude indicator.

An Electron Saved is an Electron Earned

Handheld GPS

If you turn off all the non-essential items immediately, it may allow you to run things that you might like to use when you land, such as your ILS receiver and the flaps. If you have an alternate means of navigating, you could probably turn off everything -- including the radio for ATC communications -- provided you check in regularly to provide a position report. I almost always bring my yoke mounted GPS and handheld radios as backups, and they can be a key part of your strategy to maximize your battery life when the alternator dies.

At a general aviation safety seminar at Travis AFB, I heard Rod Machado say that the most important decisions you'll make in an emergency are the ones you make before you leave the ground. In Part II, we discuss some practical solutions that you might decide to implement ahead of time so that you will have more alternatives when your alternator or electrical system decides to take a vacation.