Aircraft communication systems allow pilots, air route traffic control centers, ground personnel, airports, and other entities to maintain a bridge of communication. This is especially critical during flight as aircraft communication systems aid in avoiding unprecedented accidents, turbulent weather, and more. With so many systems set in place, this blog will provide a brief overview of each aircraft communication system, their subsystems, and how they work.
A majority of aviation communication is achieved through the use of radio waves. Aircraft radio communication is accomplished by using transmitters to send out information or data signals, and receivers are used to acquire signals that are then transformed into an output that can be interpreted on a display screen. Next, a transceiver is a communication radio that both transmits and receives signals. It is important to note that transceivers are considered half-duplex systems, meaning that communication can occur in both directions, but only one party can speak at a time.
The Air Navigation Order (ANO) indicates the minimum number and types of radio equipment that must be carried on aircraft. In fact, most radios found in aircraft are equipped with different ranges and uses. For instance, a VHF radio provides good short-range radio reception, but is rendered useless for long-distance, line-of-sight communication. In this case, you are better off using a ground effect radio transmission like a High Frequency (HF) radio.
HF communication systems are less common today with the advent of Satellite Communication (SATCOM). HF communication systems supply voice communication over long distances, allowing airplanes and ground stations to maintain contact. They operate over an aeronautical frequency range of 2 MHz to 29.999 MHz. Furthermore, they utilize the surface of the earth and the ionized layer of the atmosphere to cause the communication signal to skip or reflect. The distance between skips changes according to the time of day, radio frequency, and an airplane’s altitude.
The HF radio is also responsible for modulating an RF carrier signal with voice audio from the flight interphone system. During the signal receival, the HF radio demodulates the RF carrier signal, isolating the voice audio from the RFQ signal. At this point, the HF transceiver sends the audio to the flight interphone system. Lastly, the HF communication system consists of a radio control panel, HF transceiver, HF antenna coupler, and HF antenna.
Meanwhile, VHF radio transmission is most commonly used for short to medium-range communication. It supplies flight crew with voice and data for line-of-sight communication. Additionally, a VHF communication radio is tunable in a frequency range of 118.000 MHz to 136.990 MHz. Typically, this type of communication system consists of a radio control panel, VHF transceiver, and VHF antenna.
To manage such systems, radio management panels (RMPs) are used to centralize radio communication frequency controls. Coupled with a Selective Calling (SELCAL) system which monitors all communication radios in aircraft, the flight crew can be promptly alerted when the system receives a ground call with the correct airplane code. Most aircraft are designated a unique four-letter code for SELCAL operation, each letter representing a different audio tone. The ground stations can send the applicable tones to call an aircraft.
The SATCOM system is far more reliable than its counterparts as it uses the International Maritime Satellite Organization (INMARSAT) satellite constellation. INMARSAT satellites are located in the Earth’s geostationary orbit above the equator, and they are used as relay stations for long distance communication. This system comprises the satellite network, the ground earth stations (GESs), and the aircraft earth stations (AESs).
The Aircraft Communications Addressing and Reporting System (ACARS) is a data link communication system that allows you to transmit messages and reports between an aircraft and an airline ground station. A message or report from an aircraft to the airline ground station is usually called a downlink, while a message or report from the airline ground station to an aircraft is called an uplink. Most ACARS reports include crew identification, OOOI times, engine performance, flight status, and maintenance items.
As previously mentioned, interphone communication is integral for aircraft, allowing for contact between the cockpit and ground pilots to be maintained. As such, there is a cabin interphone system for communication between cabin crew and pilots. The service interphone system is for on-ground use and maintenance personnel only. Additionally, a ground crew call system enables crew members and ground mechanics to maintain communication. The last system that most people are familiar with is the Passenger Address (PA) system, which allows the cockpit and cabin crew to address all the passengers aboard the aircraft. A microphone and speakers also allow crew members to make announcements and provide instruction before, during, and after flight.
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