Failure to complete a flight safely after an electrical failure shouldn't be left to chance. In Part I, AVweb took a close look at the electrical system. In Part II, we describe other ways the system can fail, and present different ways to prepare for a failure before it happens.
August 20, 2003
In the previous article (Part I), I mentioned I had "an electrical failure," which suggested that I had only had one. Well, electrical failures come in all kinds of permutations, and I've had more than my fair share. I read an article about a Navy test pilot who -- while test-firing a new missile over the ocean near Point Magu, Calif., -- shot himself down. One of my first electrical failures was also self-induced.
A Switch In Time Saves ... Power
A dozen years ago, a visiting business colleague was interested in going flying. By the time we got to the airport it was dark, and I wasn't night current. So I jumped into the 172RG that I liked to rent, and prepared to do three landings and takeoffs before coming back for my colleague. I started the plane using just the battery half of the master switch as I described in Part I, and then started my pattern work while my friend watched from the ground. As I raised the landing gear, on the third takeoff, everything in the plane went dark. I was startled, but not alarmed, and maintained a constant climb angle to pattern height, and then started to circle the airport to figure out went wrong.
|Dual Master Switch
I cycled the master switches and realized my mistake: I forgot to turn on the alternator side of the master switch after starting the plane with just the battery half of the switch. It was night, and all the radios were on and lights blazing, so I had drained the battery rapidly. Although the gear is hydraulic, it uses an electric motor to pressurize the fluid. When I sucked the gear up on the third takeoff, the motor came on and the surge in current dropped the voltage to the point where I had no lights or radios.
Cycling the master switches did bring back enough power to light up the instrument panel, but the battery voltage had dropped below the point where the alternator operates, so there was no way to recharge the battery -- even though I finally had all the switches set correctly. I had to call it a night right then and there, and never got to take my friend flying. He did say that he had been wondering who was the crazy person flying over the airport without lights. The FBO had to charge the battery the next day, and -- rightly so -- they charged me for their trouble.
Transponder -- Early Warning System
Early detection of an electrical failure is important, and clearly I failed to do this while flying the 172RG. In the prior article, I mentioned detecting failures by noting the low (or high) voltage light, dimming of panel lights, and monitoring of the ammeter, load meter or voltmeter (if installed). Another warning sign is the transponder, which is often the first device on board to quit as power decreases. Although there are lots of reasons ATC may report that they've lost radar contact, one of them is that there's no longer enough power for the transponder to reply with the high-power pulse it sends -- even though your reply light and other radios may still be working fine. Whenever ATC reports they've lost radar contact, it's prudent to check your electrical system. If you are having an electrical failure, you can be assured that the other radios are next to go if you don't take immediate steps to conserve power.
In the previous article, I discussed shedding all non-essential loads to maximize battery life after an electrical-system failure. This is a fairly reactive strategy to dealing with electrical system failures. The key disadvantage to it is that you'll have relatively little idea of how much longer your battery power will last -- particularly if you didn't detect the failure early on.
Alternatively, you can pursue a proactive strategy, and provide a backup to your electrical system. The FAA considers electrical backup so important that a couple of years ago they began requiring all Part 135 operators to have electrical backup when flying in IMC. Here are a few alternatives that you might consider installing.
If One Is Good Then Two Must Be Better
A factory-supplied standby alternator may seem like a great solution -- particularly if your plane came with one. If your plane doesn't have that option installed, you may still be able to add one on. Although this sounds great, it may not be the ultimate solution. For example, friends of mine own a Cessna T210N with the second alternator and finally had it removed all together, since it failed regularly every 350 hours. At a Cessna Pilot's Association course I attended last year, they mentioned that this was not uncommon in the T210.
Alas, you say your trusty steed was not factory-designed with an option for a second alternator? You may still be in luck. B & C Specialty Products sells an engine-mounted standby alternator that's available for numerous aircraft. The unit produces 20 amps, which should handle any emergency loads. There may be other suppliers as well.
The Answer Is Blowing In The Wind
Another interesting option is a wind-driven generator. Pull a T-handle, and Basic Aircraft Products' turboalternator pops out into the slipstream and starts producing power. The output varies with speed, and is rated at 12 amps for a 28-volt system and 18 amps for a 12-volt system when flying at 150 knots. That should be sufficient power to run a transponder and one or two com radios, though you'll want to keep the speed up while flying the ILS, as the output decreases as the plane slows down.
This pop-out system is currently available for the Cessna 210, 206, Bonanzas, Piper PA-32 and Mooney M20. At this writing, they are working on an STC for the Cessna 182. A lower-cost, fixed-position 12-volt system is available for a variety of Pipers, Luscombe, Aeronca, Taylorcraft and Stearman. One possible disadvantage: You probably wouldn't want to use these in icing conditions, but then you don't want to be there anyway.
An alternative to a standby alternator is to carry another power source on board with you. AvTek offers the "Stdby Elec," which includes a lead acid battery and current-limiting circuitry built into a case that you keep in the cockpit with you. When the alternator fails, you plug the system into your cigarette lighter to provide power to your electrical system. Obviously you will be limited to the rating of the circuit breaker protecting your cigarette lighter, but this should be more than adequate to run a transponder, radio and other low-current items. Both 12- and 28-volt versions are available.
Stamp Out SPOFs
In the commercial computer industry, system architects always try to design systems to eliminate SPOFs or "single points of failure." A SPOF in an airplane would be having a single master switch and main electrical bus. If the master switch fails, having a standby alternator won't help at all.
The solutions discussed so far assume that at least some part of your electrical system is still intact, and can deliver the power supplied from your standby source. The ultimate solution (OK, so maybe it's not the ultimate, but I like it) will still deliver power to two critical systems: GPS navigation and radio communications, even if every part of your airplane's electrical system has given up the ghost. Or, assuming just your alternator died, it allows you to shut off your master switch and save whatever battery power you still have for the end of the flight when you might use it to power flaps, landing gear, fly an ILS, etc.
My favorite solution is one put together by a friend of mine who is also a member of Los Medicos Voladores (Flying Doctors), which flies volunteer medical teams to Mexico. As you might imagine, we often end up in very remote areas where one might wait days for a part or a mechanic. Therefore, you want robust backup systems.
The Ultimate Backup Electrical System
The good news is that you probably already own several key components of this system. The bad news is that today it is a do-it-yourself system, but hopefully some entrepreneur will step into the fray and package it commercially.
In its simplest implementation, the solution is to bring along one or two 12-volt, 12-ampere-hour, sealed, lead-acid batteries into the plane, and connect them to a yoke-mounted GPS and a handheld radio. When your plane's electrical system goes belly-up, pull the GPS's plug from your cigarette lighter, and plug it into the cigarette lighter receptacle that you've wired to your backup batteries. Add a second receptacle to the battery, and now you can plug in your handheld radio. Regardless of the state of your plane's electrical system, you now have hours of navigating and talk time.
Though I haven't tried these, one solution I found on the Internet that might work is the Powersonic PS-12120, 12 volt, 12 Ampere-hour battery, which weighs about 10 pounds and sells for under $50. Their PSC-12800A charger (under $60) should allow you to recharge the battery at home in around 12 hours. Write to them, not me, if you have a question.
My friend pulls his batteries from the plane after every trip and recharges them at home. That's easy to do if you're disciplined and do it every time. But the ultimate backup electrical system shouldn't require that much work. Why not create a charger that provides a continuous trickle charge from your plane's cigarette lighter to the backup battery? That way you can always have your GPS and handheld connected to the backup battery, and there are no plugs to move around when the electrical system fails. And you'll never forget to recharge the battery, or bring it back to the airport for your next flight.
This is an opportunity for an entrepreneur to design and market such a system. If you want to do that, don't bother contacting me. In the words of Nike, Just Do It! Caution: Do not connect your cigarette lighter directly to a backup battery without a charger and expect it to charge. You need a charger; otherwise you'll destroy the backup battery and possibly cause a fire or worse. Also, if you have a 28-volt system, be sure to check whether your handheld radio and GPS will work on 28 volts -- some do not.
As great as the ultimate backup electrical systems sounds, there's at least one major downside compared to the other approaches mentioned. If the master switch is off, you'll no longer be powering the turn coordinator in your panel, which you'll want if you're IMC. If you were IMC, lost your full electrical system, and then lost your vacuum system, you'd have run out of primary bank references, which is usually fatal. If that were to happen to me, I'd be referring to the yoke-mounted GPS and watching the "Track" for every indication of a heading change, and bank slightly to hold the heading constant. That's not an FAA-approved method, but it might save your bacon when all of your other options are gone.
Backup Communications -- Be Prepared
What about lost communications? In the grand scheme of things, losing two-way radio communications is inconvenient, though rarely life-threatening. It sure makes things harder, though, and anyone planning to fly much IFR should purchase a handheld radio and just consider it part of the cost of getting their instrument ticket -- the least expensive part at that.
Besides just buying the radio, there are at least three issues you should consider so you're prepared to use it when the chips are down (and no, that expression wasn't invented here in Silicon Valley). The battery issue is the obvious one, and the solutions are simple. Bring extra batteries. If you have a rechargeable pack, get a separate alkaline battery pack and bring lots of spare batteries.
If A Tree Falls In The Woods, And ATC Doesn't Hear It ...
The second issue becomes apparent if you've every tried to transmit from a handheld in the air while more than a couple of miles from an airport. The bottom line: Handheld radios can't be heard well when you transmit using their short, rubber antennas inside a metal airplane. A little antenna theory will make this obvious.
At 121.5 MHz (to pick a frequency you might use), the wavelength of the radio emissions coming from your antenna is 2.47 meters, or 8.1 feet. You've probably noticed that the windows in your plane are relatively small compared to 8 feet. And the windows are the only area the RF can get through because the rest of an aluminum airplane shields the energy from leaving the plane. The problem becomes similar to that of a relatively large bug trying to fly through a screen door -- it just can't get through very well.
To make things worse, the rubber antenna is really a compromise. Ideally, your antenna would be a quarter wavelength wire, or about two feet long at 121.5 MHz (like the telescoping antenna on the old walkie-talkies many of us played with as kids, though shorter). To make it work electrically, that two feet of wire is helically wound inside the rubber-coated antenna. Those stubby antennas are convenient and electrically they work, but they radiate very poorly compared to a full-length antenna.
Using a handheld radio in the plane, you may be only able to call the tower from a few miles out, and an approach controller may not hear you until you are well inside their airspace. I actually got chewed out by an approach controller who thought we'd left the frequency. The electrical system in a friend's C182 died, then the battery died in his handheld, and we were left with my handheld -- but couldn't be heard well because of the antenna issue.
Three Ways To Connect To An External Antenna
The solution is obvious. You need an antenna on the outside of the airplane. Fortunately, there are multiple ways to do this. In our T210, the previous owner had the coax cable from COM2 looped out through the dash, and installed a connector on the dash that goes to the COM 2 antenna. While that loop of wire looks a little strange, it is very easy to disconnect so that I can connect my handheld radio directly to the external antenna.
You can also get a splitter installed into an existing antenna cable so that two radios (one in the panel and your handheld) can share the same external antenna. Once you do this, ATC will probably hear you nearly as well as from the Com radio in your panel. AvionicsWest recommends a Honeywell P/N 071-01443-0001, which sells for around $55 and requires only one to two hours of installation.
You can also have an additional antenna installed on your aircraft for the handheld radio. This is not uncommon in CAP aircraft or other planes that want to use additional radios in the plane and have them work as effectively as possible.
Say Again, Please?
The third problem with a handheld is that it's damn inconvenient to use when you need it most. Imagine you're IMC, the electrical system has failed and you've turned off the autopilot, so you're now hand-flying the airplane. Having to pick up the radio, shout into it, and then hold it to your ear to hear the reply can be a real distraction at a time when you want to minimize distractions. Of course you're nearly deaf anyway from having to take off your $500 or $995 ANR headset so that you can hear the radio, or yell over to your passengers since the intercom no longer works. If you're ever in this situation, check first to make sure you're not just sleeping in bed having a nightmare.
The solution is to get a headset adapter for your handheld radio. When the electrical system fails, it will be relatively easy to unplug your headset from the panel and connect it to your handheld radio. And then it's a cinch to talk to ATC. Just push the push-to-talk button on the radio, and talk through your headset. Better yet, wire up a separate push-to-talk button on your yoke and connect it to the handheld radio. Worried that you can no longer talk through the intercom to your passengers? I wouldn't be. But if it concerns you, buy an inexpensive battery-powered intercom and leave it connected to your new ultimate backup electrical system.
Purists will note that -- when using a headset -- the internal microphone of some handheld radios will still be active when you hit the push-to-talk button, and will add lots of background noise to the signal you're transmitting to ATC. That may be true, and if you're worried about it, you might investigate the solution for your particular radio. In my case, I'll just talk a little louder. If it's an emergency, I don't think ATC will care about a little background noise on the signal. After all, they must already have ESP to be able to decipher the poor quality of some of the radios in the GA fleet that we hear everyday.
After you've got your backup electrical system in place, think about other single points of failure in your airplane. Just what are you going to do to mitigate the problems caused when your vacuum pump fails? If you've got a second vacuum pump, great! Or, a second artificial horizon that's electrically driven is excellent. If not, start considering your options. Although failures are a certainly, failure to complete a flight safely after an electrical failure shouldn't be left to chance!