Safety is paramount in aviation and being able to successfully communicate is one of its cornerstones. It’s why successfully maintained pilot and cabin communication systems are as critical as they can be complex.
“They use them so much that if they're not working properly, they're going to get flagged immediately. If it's not the air traffic controller telling them, "Hey, look, I cannot hear you," or the pilot saying, "I can't hear you. You're coming in weak and garbled," and things of that nature. So you pretty much can't get away with it, because that's your only voice to the ground, is communication,” said John Holland, general manager, Trimec Aviation.
However, troubleshooting an issue a pilot has in the sky when the aircraft is on the ground is not always so straightforward. Holland gives the example of trying to trouble shoot Wi-Fi connectivity issues.
“It's one of those things where the customer sometimes says it's weak and it's just not working right. And you go there and it's working perfectly for you. They don't realize that an airplane is at 35,000 feet, and you're not going to get the similar performance that you do at home,” he said.
Holland adds that Wi-Fi has become a choice more and more pilots are going with, giving them the option for text-based communications, but all around the technology is advancing.
“He's got choices today. And that's what's awesome. Everybody is getting more and more and more advanced. And, of course, without the old VHF com, that's been in the cockpit for a long time, and HF communications, which he's had across the water, basically now they're getting other capabilities, and being able to communicate mainly through CPDLC, SAT voice, which is actually a very good product that we use instead of the HF, which people really love because of the clarity of the call,” said Holland.
Trouble Shooting
The pilot’s choice of headset and/or microphone will have a considerable impact on the overall operation of the system, explained Jim Karpowitz, avionics support tech, Skycom Avionics, Inc.
“A poor microphone can make even the best of com radios sound tinny or distorted. Improper mic positioning can cause inadequate transmit audio volume – the ‘loud’ part of loud and clear. The mic must be positioned close to the mouth and foam filters over the mic will protect it from moisture and give a clean sounding audio signal,” he said.
Keeping the plugs clean is important and Flitz or similar metal cleaners should be used to keep oxidation off of the conducting surface.
“If you are getting scratchy, tinny or insufficient audio, this is a good starting spot for troubleshooting. Headset jacks should be secure and properly insulated from the airframe with non-conducting washers,” he continued.
Holland said common issues they see with VHF com are they're weak and unreadable.
“Portions of the HF systems are in an unpressurized area. So as a result, these boxes are pressurized to prevent them from internally arcing back and forth. And they'll lose their pressurization. And, as a result, they may have poor performance. So you can normally have just weak reception, or garbled when you're trying to transmit,” he said.
Cleanliness is another important aspect to be mindful of.
“Cleanliness and condition of connectors both in the tray and in the radio are critical elements in proper function. Most connectors are gold plated, and conditioning compounds such as Stabilant 22 or DeOxit Gold are helpful in maintaining the critical connections that make the radio work correctly,” said Karpowitz.
And corrosion can be a leading cause of issues, especially when they lead to power issues.
“Power problems are often a root of malfunctioning avionics. Poor crimps, resistive circuit breakers, corrosion, wandering system voltage and bad grounds can all add up to a com system that will not work and play well with others,” said Karpowitz.
Of course, other issues can be found with the users of the aircraft. Wi-Fi issues, for example, can often be caused by there being simply too many people on a network.
“All they know is they're frustrated. And, hey, look, it's not working right. It's not working right. It's too slow. It's too slow. When, really, there's nothing wrong with the system. And the reason why I say there's nothing wrong with the system is that most of those systems are shared networks. So you might have, let's just say, eight people in the airplane. And you got someone in the back that's streaming. Well, of course, that streaming's going to really impact the performance of everybody else trying to utilize the system,” said Holland
For satcoms, Holland said the issue of multiple users is multiplied.
“Satcoms, which is the equivalent of the ground based systems, are even worse. Because you're not only sharing the bandwidth with your airplane, but you're sharing the bandwidth with everybody that's within your range. And that's including boats. So if you're over the water, the boats could be a problem as well,” he explained.
And some com problems may be externally induced by consumer-grade devices operating in the cabin. Digital devices and USB power supplies are particularly notorious for causing annoying breakthrough squelch problems and other flaky operation in an otherwise properly functioning system, explains Karpowitz.
“Very Importantly, do not try to rectify squelch break issues merely by turning the squelch up. If a com system is properly calibrated and you get squelch break in the aircraft, the problem is noise, and noise needs to be dealt with at the source,” he notes.
Karpowitz said to watch for obvious issues such as radios that are not locked completely into the tray or antenna connectors that are loose.
“Sometimes these can be disturbed during inspections or other service work. Make sure the connectors and units are secure and can pass the tug test. It is possible to inadvertently switch antennas because the connectors and cables are used in a variety of systems, Nav, Com, GPS, etc.,” he said.
Antenna Trouble
Antennas can be another leading cause of communication disfunction.
“If the antennas on top of the fuselage are not at a proper distance, they could interfere with one another. And it's the same thing too with any Iridium or Satcom system that you put on board. And you get it too close to a GPS antenna, which can also impact the performance of the GPS. I mean, it can literally cause the GPS in the cockpit basically to lose coverage,” said Holland.
Not only are antennas critical but their installation and location are vital elements of proper system operation. Most avionics installation manuals specify minimum distances between antennas or between antennas and potential noise sources or vulnerable systems. As much as possible, antenna cables should be routed separately of signal, digital or power cable bundles for a variety of reasons, said Karpowitz.
“In an era of so many composites and other non-metallic aircraft building materials, VHF com antennas can suffer degraded performance by not having enough of a ‘ground plane.’ Think of a ground plane as a mirror – the other half of a two part antenna. If a typical antenna is mounted on a non-metallic surface, the lack of ground plane will severely compromise the efficiency of the antenna and may even result in unstable system operation,” he continued.
The condition of the antennas and associated cables is critical to the proper function of a communication system. The antenna is the last point of contact for the transmitter and the first for the receiver. If it is damaged or compromised, it will negatively impact both the range and quality of the transmitted and received signal.
“Old RG-58U cable with the black insulation that has been around for so many years is no longer considered suitable for aviation use. Beyond its relative fragility, vulnerability to temperature and moisture and penchant for releasing toxic material in a fire, it will degrade with age. It is strongly advisable to remove RG-58 cable in favor of RG-400, preferred, or RG-142, low loss, but stiff and it also has a steel core that can become magnetized,” said Karpowitz.
Along with the do's and don'ts of antenna placement, Holland said to make sure that you follow the guidelines on exactly where to put this.
“Now, let's just say you don't have any room. There are filters that you can use to help eliminate that particular problem. But, if it's transmitting, I mean, and a GPS antenna's nearby, you're not going to eliminate that problem unless you give it space,” Holland continued.
Helicopters are especially problematic in this regard, added Karpowitz.
“It is important that antennas are not located near pilots or passengers heads in helicopters because the large windows do not provide any shielding. RF can get back into the com system through the headset or headset cable and cause howl and garbled audio. In general, try and keep the antennas and the occupants’ headsets as separate as possible,” Karpowitz said.
When testing any of these communication systems, Karpowitz notes that some com testing requires calibrated equipment to adequately assess the health of the system.
“Measuring antenna SWR, measuring frequency and accurately setting squelch levels are relevant examples. Poorly matched or malfunctioning antennas can cause damage to transmitters, besides limiting your range. For general testing, remember that talking with the tower or unicom is unlikely to give an accurate picture of how healthy the com system is. If the receiver sensitivity is poor or the transmit output is insufficient, you may not see it until you get a few miles out,” 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 proper modulation, he continued.
