Dos and Don’ts of Communication System Maintenance

Safety is paramount in aviation and being able to communicate successfully is one of its cornerstones. This is why successfully maintained pilot and cabin communication systems are as critical as they can be complex.

“They use them so much that if they don’t work properly, they’ll be reported immediately. If it’s not the air traffic controller saying, “Hey look, I can’t hear you,” or the pilot saying, “I can’t hear you. You come in weak and scrambled,” and things of that nature. So you pretty much can’t get away with it, because it’s your only voice on the ground, it’s communication,” said John Holland, general manager of Trimec Aviation.

However, troubleshooting a problem experienced by a pilot in the sky when the aircraft is on the ground is not always so straightforward. Holland is setting an example of trying to fix Wi-Fi connectivity issues.

“It’s one of those things where the customer sometimes says it’s weak and it doesn’t work well. And you go there and it works perfectly for you. They don’t realize that an airplane is at 35,000 feet and you won’t get the same performance as you do back home,” he said.

Holland adds that Wi-Fi has become a choice for more and more pilots, giving them the ability to communicate by text, but everywhere the technology is advancing.

“He has choices today. And that’s what’s great. Everyone is getting more and more advanced. And, of course, without the old VHF comms, which has been in the cockpit for a long time, and the HF comms, which he had across the water, basically now they get other capabilities , and can communicate primarily via CPDLC, SAT Voice, which is actually a really good product that we use instead of HF, which people really love because of the call clarity,” Holland said.

Repair

The pilot’s choice of headset and/or microphone will have a significant impact on the overall operation of the system, explained Jim Karpowitz, avionics support technician, Skycom Avionics, Inc.

“A poor quality microphone can make even the best of com radios sound tinny or distorted. Improper mic placement can result in inadequate transmit audio volume – the “loud” part of loud and clear. The mic should be placed close to the mouth and foam filters on the mic will protect it from moisture and give a clean audio signal,” he said.

It is important to keep the plugs clean and Flitz or similar metal cleaners should be used to prevent oxidation of the conductive surface.

“If you get erratic, thin, or insufficient sound, this is a good starting point for troubleshooting. Headphone jacks should be secure and properly isolated from the cartridge with non-conductive washers,” he continued. .

Holland said common issues they see with VHF com are that they are weak and unreadable.

“Some parts of the HF systems are in an unpressurized area. Therefore, these cases are pressurized to prevent them from arcing internally back and forth. And they will lose their pressurization. And, as a result, they may perform poorly. So you can normally get weak or scrambled reception when trying to transmit,” he said.

Cleanliness is another important aspect to consider.

“The cleanliness and condition of the connectors both in the tray and in the radio are critical to proper operation. Most connectors are gold plated and conditioning compounds such as Stabilant 22 or DeOxit Gold are helpful in maintaining the critical connections that allow the radio to function properly,” Karpowitz said.

And corrosion can be one of the biggest causes of trouble, especially when it leads to power issues.

“Power issues are often the cause of avionics malfunction. Bad crimps, resistive breakers, corrosion, errant system voltage, and bad grounds can all add up to a communications system that won’t work and play well with others,” Karpowitz said.

Of course, other problems can be found with aircraft users. Wi-Fi issues, for example, can often be caused by too many people on a network.

“All they know is that they are frustrated. And, hey, look, it doesn’t work out well. It doesn’t work well. It’s too slow. It’s too slow. When, really, there is nothing wrong with the system. And the reason I say there is nothing wrong with the system is that most of these systems are shared networks. So you could have, let’s just say, eight people on the plane. And you have someone behind broadcasting. Well, of course, this streaming is really going to impact the performance of anyone trying to use the system,” Holland said.

For satcoms, Holland said the problem of multiple users is multiplied.

“Satcoms, which are the equivalent of ground systems, are even worse. Because you’re not only sharing bandwidth with your aircraft, but you’re sharing bandwidth with everyone within range. And that includes boats. So if you’re over water, boats could be a problem as well,” he explained.

And some communication problems may be externally induced by consumer devices operating in the cabin. Digital devices and USB power supplies are particularly notorious for causing annoying squelch issues and other erratic operations in an otherwise properly functioning system, Karpowitz explains.

“Very important, don’t try to correct muffler break issues simply by increasing the muffler. If a communications system is properly calibrated and you get a muffler break on the plane, the problem is the noise, and the noise must be treated at the source,” he notes.

Karpowitz said to watch for obvious issues such as radios that aren’t fully locked into the tray or antenna connectors that are loose.

“Sometimes these can be disturbed during inspections or other maintenance work. Make sure the connectors and units are secure and can pass the pull test. It is possible to inadvertently change antennas as the connectors and cables are used in a variety of systems, Nav, Com, GPS etc. “, did he declare.

Antenna problem

Antennas can be another major cause of malfunctioning communication.

“If the antennas above the fuselage are not at an appropriate distance, they could interfere with each other. And it’s the same also with any Iridium or Satcom system you put on board. And you bring it too close to a GPS antenna, which can also impact GPS performance. I mean, it can literally lose GPS coverage in the cockpit,” Holland said.

Not only are the antennas essential, but their installation and location are vital to the proper functioning of the system. Most avionics installation manuals specify minimum distances between antennas or between antennas and potential sources of noise or vulnerable systems. Whenever possible, antenna cables should be routed separately from signal, digital or power cable bundles for a variety of reasons, Karpowitz said.

“In an age when there are so many composites and other non-metallic aircraft construction materials, VHF communications antennas can suffer performance degradation by not having enough ‘ground plane’. Consider a mirror-like ground plane – the other half of a two-piece antenna.If a typical antenna is mounted on a non-metallic surface, the lack of a ground plane will severely compromise the effectiveness of the antenna and may even result in unstable system operation,” he continued.

The condition of antennas and associated cables is critical to the proper functioning of a communications system. The antenna is the last contact point for the transmitter and the first for the receiver. If damaged or compromised, it will negatively impact the range and quality of the transmitted and received signal.

“The old RG-58U cable with the black insulation that has been around for so many years is no longer considered suitable for aviation. Beyond its relative fragility, vulnerability to temperature and humidity and its propensity to release toxic materials during a fire, it will degrade with age.It is strongly advised to remove the RG-58 cable in favor of the RG-400, preferably, or the RG-142 , low-loss, but stiff and also has a steel core that can magnetize,” Karpowitz said.

In addition to the do’s and don’ts for antenna placement, Holland said to make sure you follow the guidelines on exactly where to place this.

“Now let’s just say you don’t have room.” There are filters you can use to help eliminate this particular problem. But, if it’s transmitting, I mean, and a GPS antenna is nearby, you’re not going to eliminate that problem unless you give it space,” Holland continued.

Helicopters are particularly problematic in this regard, Karpowitz added.

“It is important that antennas are not located near the heads of pilots or passengers in helicopters as the large windows provide no shielding. cause screaming and garbled audio. In general, try to keep antennas and occupant headsets as separate as possible,” Karpowitz said.

When testing any of these communication systems, Karpowitz notes that some communication tests require calibrated equipment to properly assess the health of the system.

“Antenna SWR measurement, frequency measurement and fine tuning of squelch levels are good examples. Badly adapted or defective antennas can damage the transmitters, in addition to limiting your range. For general testing, remember that speaking with the tower or unicom is unlikely to give an accurate picture of the health of the communications system. If the receiver sensitivity is poor or the transmission output is insufficient, you may not see it until you’ve driven a few miles,” he said.

Five to ten miles is a good range for general performance testing. At these distances, background noise should be minimal, indicating adequate signal strength, and volume should be good, indicating appropriate modulation, he continued.