Maintenance & Restoration: Listening for Trouble

One area where many pilots find themselves challenged in their situational awareness ... ferret out these problems, as well as some of the problems that can be ...
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maintenance & restoration Listening for Trouble Looking for signs of avionics problems GEORGE WIL HE L M SE N


s pilots, we pride ourselves on being able to maintain a strong level of situational awareness as we fly. This is drilled into us from the start of our pilot training, because when problems occur in an airplane you generally can’t pull over to the side of the road for a spell to address them. One area where many pilots find themselves challenged in their situational awareness can be in their avionics stack. Part of this uncertainty comes from the fact that the avionics in the instrument panel are a mystery to most pilots. Unlike the airplane engine, whose function can be reasonably described by most pilots, or the controls, which are actuated by rods or pulleys and cables, if you were to ask a dozen pilots how the avionics accomplish their tasks, you would be more likely than not to get a blank stare than an answer. However, by listening and looking, pilots may gain skills that will allow them to diagnose minor avionics malfunctions before they reach the point of a failure or incorrect use that may challenge their ability to fly their plane in difficult conditions. To help build knowledge in this area, we’ll go over some of the most common things that pilots can both look and listen for in their avionics to ferret out these problems, as well as some of the problems that can be encountered. There are two places where you will be able to listen for feedback on the condition of your avionics—internally, from what you can hear, and externally, from what people can and will tell you. If you are tuned in to the key phras-

es that indicate an avionics problem, you will be able to ask a few questions, take a few actions, and identify your problem. There is a distinct advantage to narrowing down your problem, since the more details you can get, the better you will be able to either personally troubleshoot the problem, or describe the problem to your local avionics shop for its diagnosis. The latter is important because you are being charged from the moment an avionics shop technician starts troubleshooting a problem. By taking the time to try to ferret out some of the symptoms yourself, you can cut down the shop’s diagnosis time and—at shop rates of $65 to $100 per hour— potentially save yourself a bundle of money. There is one important point to keep in mind. “Older” in reference to avionics means radios that are pre-digital. This includes the majority of avionics produced before 1970. This distinction is important, since these radios typically did not employ the precision gold-plated, corrosion-resistant pins that started to be used with the digital avionics.

By taking the time to try to ferret out some of the symptoms yourself, you can cut down the shop’s diagnosis time and–at shop rates of $65 to $100 per hour–potentially save yourself a bundle of money.

Say Again Let’s look at an example. If you are flying and you keep hearing that you need to repeat your transmissions because they are broken up or hard to understand, it may be time to take your avionics in for a checkup, or at least, try a few easy fixes to clear up the problem. Depending on the vintage of the plane, brass jacks and plugs on the microphone and even the headsets can EAA Sport Aviation


maintenance & restoration corrode, and cause communication problems. Before you take your plane in for service for such issues, it never hurts to use some fine steel wool or abrasive pads to clean off the connectors. Be careful to use materials containing no soaps, since soap residue can cause problems. If you use any abrasives, be sure to take a moment and wipe off the connectors with a clean cloth to remove any leftover abrasive materials. Once the connectors on the microphone and headsets are clean, take your microphone and headset plugs and run them in and out of the jacks around 10 times to clean off the corrosion in the jacks themselves. By removing any fine layers of corrosion,

you can improve the connection and fix the transmission or headset receiving problem. If cleaning the connectors doesn’t resolve the problem, you need to do some more thinking and troubleshooting. If you are using older avionics, the same problem that can happen to headset connectors is also a problem in the radios. This means that if you can get the right tool, you can remove the radio from the rack a few inches, and then put it back in to reseat its connectors. Repeating this same action several times will help to rub the corrosion off the connections, returning them to functional condition. Another internal problem is simple,

and comes up when you can’t hear any transmissions. This can usually be tracked down to your audio selector switch or to the panel that is used to select whether the speaker or headphones or both get the audio output. This problem is usually caused by one of three things, the first of which is to make sure you have the correct radio selected to where you want the output to go. If the correct radio is selected, and you are using an older audio panel or switching system, cycle the switch or push button around 10 times. What you are trying to do with this action is clean up the switch contacts and, by doing so, remove corrosion from the contacts. Many older audio pan-

Courtesy of Paul Novacek and the Aircraft Electronics Association Avionics Advisory Board

From the Pilot’s Avionics Troubleshooting Guide


JUNE 2006

els and switches used in aircraft have self-cleaning contacts, but these contacts require use to self-clean. As such, cycling the switches is one way to clean the contacts, and restore the function of your avionics. Just as older avionics can get dirty connectors, the same thing can happen to your audio selector panel. If these simple fixes don’t solve your problem, be sure to pull and reinstall your older audio selector panel a few times. Just as it would for your nav/ comm or distance measuring equipment (DME), this approach may also clean up the contacts and may restore your audio to normal levels. While you are at it, if you are using headphones, run your hands gently over the wires between the headsets and the jacks, looking for bumps or pinched areas. If you find a significant bump or a pinched area, you may have found a problem with your headsets that needs to be corrected. A resolution may entail anything from a cord replacement to having to send the headsets in for service. If these owner-friendly techniques don’t solve your problem, it is probably time to bite the bullet and take your plane to an avionics shop. Before you go, take the time to visit the Aircraft Electronics Association’s web page at, and download the free Pilot’s Avionics Troubleshooting Guide. This handy reference card may help you to provide the right input to your avionics shop about your problem. Using the card can in many cases help to save the avionics shop time, which will help minimize your costs.

Other Odd Noises and Problems There are still other odd noises and problems out there you can hear, and with the right ear diagnose and have corrected. One such problem that turns up on a routine basis is alternator noise. This is typically heard as a whine, which follows the EAA Sport Aviation


maintenance & restoration engine speed by getting higher in pitch as the engine rpm increases, and lower in pitch when the engine rpm decreases. This problem can be caused by poor filtration of the alternator output, or failed diodes in the alternator, or a bad connection. The connections are the easiest to address, so take a few moments to disassemble, clean, and reassemble the connections between the battery and the alternator. While you are at the battery, don’t forget to check the ground connection. Some pilots fail to check this connection, since it “just goes to ground.” However, a problem in the ground or negative connection can have the same effect as the positive or hot connection. When you clean the alternator connections, don’t forget to clean up the voltage regulator wire connection to the alternator at the same time. While not carrying a lot of current, corrosion products can build up over time, and cause problems with the charging circuit. It is important to note that most electrical connector problems are subtle, and may not be visible to the naked eye unless the connection is inspected. To check your alternator for a blown diode, you can take your plane to a shop that has an oscilloscope, and watch your alternator output. You should see a nice square wave, for the most part. However, if you see ripples at odd intervals or even regularly, you likely have a blown diode, and need to have your alternator serviced to correct the condition. On rare occasions, we have found that alternator output filters, which are basically big capacitors, failed. How-

ever, if you have exhausted the other potential sources, this is a fairly inexpensive component to replace. Another source of noise in avionics is the magnetos on your airplane. Just as it did with the alternator, magneto noise will vary with the engine rpm. One way to check this is to switch to the left magneto in flight, and see if the problem goes away. If the problem doesn’t go away, you can switch to the right magneto and see if that does the trick. If the noise is better on one magneto than the other, but can be heard on both, you probably have problems with both harnesses, or the spark plugs connected to them. Depending on the vintage of your ignition harness, you can either replace the entire harness, or a single lead. If your ignition harness is more than 10 years old, or has cracks visible in the outer insulation, it is probably overdue for replacement anyway. The cost of these harnesses isn’t exactly low, but the improvement they can make in the performance of your avionics can be surprising. By keeping your ears open when you fly, you can self-identify and do some pretty effective troubleshooting of avionics problems. If you don’t have a copy already, be sure to download a copy of the Aircraft Electronics Association’s Pilot’s Avionics Troubleshooting Guide, and use it to help you in your search. In the end, your own know-how and knowledge can help to ferret out many problems, and in doing so, either allow you to make the necessary corrections or, at the least, provide accurate information to the avionics shop to help minimize the cost of troubleshooting.

Many older audio panels and switches used in aircraft have self-cleaning contacts, but these contacts require use to self-clean.


JUNE 2006