Avionic Systems Communications PDF

Intercom System Sound Audio frequencies are those perceptible by the human ear. All sound is produced by mechanical vibrations. When something vibrates, it alternately compresses and expands the air around it. When they come closer, they are known as compressions. When they move further, they are kn...

Intercom System Sound Audio frequencies are those perceptible by the human ear. All sound is produced by mechanical vibrations. When something vibrates, it alternately compresses and expands the air around it. When they come closer, they are known as compressions. When they move further, they are known as rarefactions. These condensations and rarefactions are transmitted to adjacent air particles. Therefore, some of the energy of a vibrating surface is transmitted away from it and may affect our hearing mechanism, providing the vibrations we can hear. All of the different sounds we hear are caused by minute pressure differences in the air around us. Sound travels through the air as longitudinal waves. The most important, and technically the most impressive, of sound receivers is the ear—it can detect sound density changes of less than one ten-millionth of 1 percent. This figure corresponds to a particle displacement of less than 0.0000001 millimeters. The pitch of the sound is determined by its frequency: the rate at which the vibrations occur. The unit of frequency is called a Hertz (Hz); 1 Hz is equal to 1 vibration per second or one cycle per second. The human ear is sensitive to frequencies between about 20 Hz and 20 000 Hz. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 240 of 356 Basic Intercom System Intercom systems are necessary due to the noise in the cockpit area of aircraft. Without the system, communications have a great risk of being misunderstood or unheard, which can result in dangerous situations developing during flight. Basic intercom system The basic intercom system consists of microphones, speakers/ headsets and amplifiers. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 241 of 356 Microphones A microphone is a transducer which changes sound into electrical signals (current or voltage). The signals can then be transmitted, amplified, recorded electrically and finally converted back into sound. All microphones contain a thin membrane, either a diaphragm or a ribbon. The membrane vibrates in response to the sound striking it. A transducer connected to it generates an electrical signal that is equivalent to the vibrations in frequency and amplitude. There are several different technologies commonly used to accomplish this conversion; two of the simpler methods are: Carbon microphones Dynamic microphones. Carbon Microphones The oldest and simplest microphone uses carbon dust. This is the technology used in the first telephones and is still used in some telephones today. The carbon dust has a thin metal or plastic diaphragm on one side. As sound waves hit the diaphragm, they compress the carbon dust, which changes its resistance. By running a current through the carbon, the changing resistance changes the amount of current that flows. Carbon microphone 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 242 of 356 Dynamic Microphones A dynamic microphone takes advantage of electromagnetic effects. When a magnet moves past a coil of wire, the magnet induces current to flow in the wire. In a dynamic microphone, the diaphragm moves either a magnet or a coil when sound waves hit the diaphragm, and the movement creates a small current. Dynamic microphone This current is the audio signal. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 243 of 356 Crystal Microphones Crystals which demonstrate the piezoelectric effect produce voltages when they are deformed. The crystal microphone uses a thin strip of piezoelectric material attached to a diaphragm. The two sides of the crystal acquire opposite charges when the crystal is deflected by the diaphragm. The charges are proportional to the amount of deformation and disappear when the stress on the crystal disappears. Early crystal microphones used Rochelle salt because of its high output, but it was sensitive to moisture and somewhat fragile. Later microphones used ceramic materials such as barium titanate and lead zirconate. The electric output of crystal microphones is comparatively large, but the frequency response is not comparable to a good dynamic microphone. Crystal microphone 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 244 of 356 Speaker/Headset A speaker or headset is a transducer which converts an electrical signal (varying in frequency and amplitude) into sound. Speaker The current reaches the speaker, and the coils of wire in the speaker turn it back into actual movement that causes the air surrounding the speaker to vibrate, which results in sound again. A microphone produces a very low voltage signal, while the speaker needs a much higher signal to work. Amplifier The device that sits between the microphone and the speaker is the amplifier. The amplifier will increase the small audio input voltage to a higher power audio signal to drive a speaker. Speaker volume (amplifier gain) is controlled by the volume knob. Push to Talk When the button is pushed, the microphone signal is input to the intercom amplifier. The push-to-talk (PTT) button can be replaced by “hot mikes.” With hot mikes, the initial audio signal switches on the amplifier, eliminating the need to press the transmit button. The down side is that any grunt, groan or even breathing is transferred over the intercom. In many applications, there is a switch to select either “hot mike” or to Press to Transmit (PTT). 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 245 of 356 Aircraft Intercom System Aircraft Intercom Systems (AIS) use audio signals to permit communication between various points in and around the aircraft. The small aircraft intercom previously only had the facility for two users (pilot, co-pilot or student). In larger aircraft, the system functions on the same basis, with more inputs applied to an amplifier and additional control facilities incorporated so certain intercom stations can be selectively included or omitted from conversations. For example, just pilot to co-pilot with all others excluded, or captain to all flight crew for a broadcast message. Large aircraft have intercom systems so that the cockpit crew can communicate with the cabin crew and vice versa. Aircraft intercom system An intercom system and an interphone system operate in a similar manner; the difference is who uses the systems and where the phone jacks are located. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 246 of 356 Flight Interphone On larger passenger aircraft, the flight interphone is primarily used for communication among the captain, first officer, flight engineer, observer’s crew station and the radio equipment compartment. Service Interphone The service interphone connects the flight compartment with various stations in and outside the aircraft. Service interphone Service Interphone jacks are located at the following: External power panel Electronic equipment bay Fueling station Right main wheel well Left main wheel well Aft cabin APU service area. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 247 of 356 Interphone locations Phone jacks are locations where a handset or headset can be connected. The handset or headset contains a microphone, a small speaker and a push-to-talk button. The phone jacks and wiring are connected to an audio amplifier so that the volume can be controlled. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 248 of 356 Cabin Interphone The cabin interphone system uses the attendant panels’ telephone-style handsets to select: Another attendant station Flight/interphone system Public address system. A handset is shown, and operation requires lifting the handset from the cradle, selecting the audio system required and pressing the push-to-talk button. Cabin attendant’s handset The passenger address system overrides the aural in-flight entertainment system so that no passengers can inadvertently miss vital or emergency information due to wearing a seat headset. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 249 of 356 Modes of Communication Three modes of communication are used in the aircraft industry: Simplex Half-duplex Full-duplex. Simplex This term is given to a system restricted to signal flow in one direction only. Simplex is used for airport terminal weather reports, telemetry and control, marker beacons and radio broadcasting. Half-Duplex Half-duplex is a two-way communications system where the signal flow is in one direction at a time. Air-to-air, air-to-ground and some data communications systems are good examples. Only one source may transmit at a time, hence the familiar radio procedures of using words like “over” and “out.” Full-Duplex This is the term given to the signal flow in both directions at the same time without interfering with any other user. Intercom and telephones are examples where both persons having a conversation can talk and listen at the same time. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 250 of 356 Radio Transmission and Reception Introduction to Radio Transmission and Reception Once an audio signal has been converted to an electrical signal, it can be transmitted using wiring in an intercom system over long distance. Radio systems also do the same using the atmosphere as the transmission medium. EM Waves An electric current transmitted along a conductor develops an electromagnetic (EM) field. Electromagnetic (EM) field When current is applied to an antenna, it generates an EM field. EM waves radiate in all directions at the speed of light and are detected by receiver antennas. The radiated EM field induces a small current in receiving antenna, and the current is amplified, reproducing the originally transmitted signal. Only AC produces an expanding and collapsing field which radiates EM waves. The antenna length required to effectively transmit an EM wave is critical and is dependent upon the wavelength of the frequency to be transmitted. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 251 of 356 Modulation Human voice frequencies for normal speech can be anywhere from a low of about 90 hertz for a deep bass to as high as 10 kilohertz for a high soprano. The most important frequencies in the speech spectrum lay between 300 Hz and 3 kHz. The minimum frequency range that can be used for the transmission of speech is 500 to 2000 hertz. The average range used on radiotelephone circuits is 250 to 2750 hertz. Frequencies contained within the human voice can be transmitted over telephone lines without difficulty, but transmitting them via radio circuits is not practical. This is because of their extremely long wavelengths and the fact that antennas would have to be constructed with long physical dimensions to transmit or radiate these wavelengths. Generally, antennas have radiating elements that are 1/4, 1/2, 1, or more full wavelengths of the frequency to be radiated. The wavelengths of voice frequencies employed on radiotelephone circuits range from 1 200 000 meters at 250 hertz to 109 090 meters at 2 750 hertz. Even a quarter-wave antenna would require a large area, be expensive to construct, and consume enormous amounts of power. Frequency vs. wavelength Using a process called modulation, the voice signal to be transmitted is impressed onto a radiofrequency wave called a CARRIER. This carrier is sufficiently high in frequency to have a wavelength short enough to be radiated from an antenna of practical dimensions. For example, a carrier frequency of 10 megahertz has a wavelength of 30 meters. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 252 of 356 Modulation Types To modulate a radio wave, we must change either of the characteristics of the wave: the amplitude or the frequency. Amplitude Modulation If we change the amplitude of the signal corresponding to the information we are sending, we are using amplitude modulation, or AM. AM carrier wave modulation The main disadvantage of AM is that most natural and man-made radio noise is AM in nature, and AM receivers have no means of rejecting that noise. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 253 of 356 Frequency Modulation To overcome amplitude noise of AM, instead of modulating the amplitude, the frequency can be modulated. In this way, the effects of amplitude noise are minimized since the recovered audio is dependent only on the frequency and not the amplitude. FM carrier wave modulation Frequency Modulation (FM) communications always use the VHF or UHF band because the other bands are too small to carry sufficient FM broadcast channels due to the high bandwidth required. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 254 of 356 Frequency Bands A band is a small section of the spectrum of radio communication frequencies in which channels are usually used or set aside for the same purpose The International Telecommunication Union (ITU) states that “the radio spectrum shall be subdivided into frequency bands.” Frequency bands Modes of Propagation Radio wave propagation modes 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 255 of 356 VLF, LF and MF bands when transmitted use antennas which maximise the production of ground waves. Generally, the transmitters are high power (hundreds of kilowatts) and the radio waves generated follow the surface of the earth and can travel thousands of kilometers. USS Harold E Holt VLF communication station (Western Australia) The United States Navy communication station at Northwest Cape (WA) transmitted frequencies between 12 kHz and 27 kHz. These low frequencies penetrate water to a depth of approximately 20 metres, making then suitable for submarine communications. The tallest tower of the array (tower zero) is 1372 ft (418 m) tall, transmitting nominally 2 MW but can go as high as 5 MW if required. The antenna array covers nearly 1000 acres of land, illustrating that transmitting low frequencies requires huge equipment and massive power. The groundwave component of a HF transmission is absorbed rapidly by the earth; approximately 8 km sees it out. A transmission in the HF band (skywave) refracts through the ionospheric layers, returning to earth thousands of miles from the transmitting station. HF is used for voice communication over long distances and allows communication between aircraft or between ground stations and aircraft. Radio waves in the VHF/ UHF bands are not refracted sufficiently by the ionosphere and normally pass through it and become lost to space. If transmitted as groundwave, losses are severe, and so the propagation mode used for these frequencies is line-of-sight (space waves). 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 256 of 356 Aircraft Radio Communication Systems HF Communications The HF system operates in the aeronautical frequency range of 3 MHz to 29.999 MHz using AM modulation. Generally, aircraft that carry HF radios can operate long distances over water or in the remote regions of the earth and are used for Air Traffic Control (ATC) purposes. HF radios have the capability of transmitting worldwide compared to a maximum of only about 400 km (air to ground) for VHF communications. Long range HF is achieved by using sky waves refracted through the ionosphere. Range is dependent upon frequency selected and time of day (ionosphere) and so on. Aircraft HF transmitters produce an output of 80–200 watts, which is much higher than the output power found with VHF transmitters to achieve long-distance communications. HF is more affected by atmospheric interference than VHF, and sometimes an aircraft over the middle of an ocean will lose communication because of thunderstorms or similar disturbances. Antennas Long wire antennas as shown on the Lockheed Electra (Orion maritime aircraft) are still commonly incorporated on modern aircraft with HF. On a light aircraft, the antenna runs from a wingtip to the tail and then down through a feed-through to the HF transceiver. They usually employ a weak point so that if they do break, they’ll separate from the aircraft before wrapping around something and causing damage or loss of control. Long wire high-frequency antenna Jet aircraft rarely have them because of the vibration and the increased risk of damage at high speeds. Usually the antenna forms part of the airframe. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 257 of 356 HF antenna in leading edge of tail VHF Communications VHF radio communication in aviation operates in the frequency range of 118 MHz to 136 MHz using AM modulation. VHF provides much clearer reception and is much less affected by atmospheric conditions. The electromagnetic waves in the VHF band are space waves, so they are limited to line of sight. At 1000 feet the range is approximately 60 km. The maximum range using ground-based stations is approximately 400 km to aircraft above 35 000 ft. Much less power is required for VHF than HF communications, with VHF power outputs between 5 and 20 watts. VHF antennae 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 258 of 356 The transmitter only needs to have reasonably low power to contact air traffic control because normally the pilot is reasonably close to the tower. The pilot selects the appropriate channel assigned to a tower frequency and then transmits. VHF is the standard radio communications frequency band for ATC purposes. Over longer distances, HF provides the additional range for communications. The formula (not examinable) for finding transmit distance in VHF is: 1.23 × (√ ht + √ hr) ht height of the transmitter in feet hr height of the receiver in feet. Example What is the VHF horizon in nautical miles (NM) for an aircraft flying at 10 000 ft? 1.23 × (√ 10000 + √ 0) 1.23 × 100 123 N M UHF Communications UHF installations are generally like VHF systems using line of sight propagation and low output powers of up to 20 watts. Generally, the system antennas are of the small-blade type. UHF transceivers are used predominately by the military. UHF antenna 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 259 of 356 Radio Transceiver A radio communications transmitter and receiver perform similar functions and can use much of the same hardware. A receiver and transmitter are built into the same unit called a transceiver. Radio communication transmitter and receiver A microphone converts the sound waves to electrical signals that are then combined with a carrier wave in the transmitter using AM or FM modulation. The transmitter applies the signal to an antenna, and electromagnetic waves are radiated from the antenna. The transmitter circuits of the radio transducer are energised whenever the push-to-transmit button is pressed. A receiver tuned to the same carrier wave frequency receives the modulated carrier wave and then separates the audio signal from the carrier wave using a demodulator. The audio output from the demodulator is amplified and drives a speaker or headset to reproduce the sound waves that were picked up by the transmitter microphone. In a transceiver the receiver circuits function whenever the radio is turned on (like your transistor radio receiver) until the push-to-transmit button is pressed, when the receiver function will be replaced by the transmitter function. This also illustrates why radio communications are half duplex. The transmission line and antenna can only be used to either transmit or receive at one time, and some of the shared internal transceiver circuits can only be used in transmit (TX) or receive (RX) modes. To achieve full duplex transmission, two separate receiver/transmitter systems are required, thus increasing overall weight and space required by the installations. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 260 of 356 Radio transmissions are not point to point, and the transmission may be received by any radio receiver within the broadcast area. Radio Control Panel A radio controller provides the means to interface the system components and to control radio system function. It provides an on/off switch, the control of volume, the selection of preset frequencies or the ability to tune to a desired frequency. The press-to-transmit button is normally remotely located on the control column. Typical radio control panel The frequency shown on the radio control panel display is that of the carrier frequency which is being modulated by the audio. To demodulate the incoming radio transmission, the receive must be tuned to the same carrier frequency. On digitised modern aircraft, radio control may be performed via a Flight Management System (FMC) Control Display Unit (CDU), with no dedicated radio control panel fitted in the cockpit, except for the volume control and Press-to-Talk (PTT) switches. All frequency selections, tuning and mode control can be performed through the FMC keypad and display. The transceiver is installed in an equipment bay, and the antenna is mounted on the skin on the upper or lower surface of the fuselage. It is common to have “in-use” and standby frequencies available to facilitate ease and speed in switching from a primary to a secondary frequency, for example, approach control and Surface Movement Control (SMC). 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 261 of 356 Electromagnetic Radiation Hazards Overexposure to radiation may cause serious health problems. You must be aware of the safe working distances near operating antennas. RF burns or electric shock may result from touching the antennas or metallic objects in the radiation field near antennas. (HF antennas can have 1000’s of volts present when transmitting.) RF radiation can be dangerous to personnel & equipment. Electromagnetic warning 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 262 of 356 ARINC Control and Reporting System Introduction to ARINC Control and Reporting System The ARINC Control and Reporting System (ACARS) solution was developed and implemented by ARINC (Aeronautical Radio Incorporated) in the mid-1970s. A substantial amount of information transmitted between Airline Operations Controllers (AOC) and aircraft is routine in nature and can be communicated by automated systems rather than by voice communications, which are slow and distract the flight crew from their primary task of flying the aircraft. Information transmitted from the aircraft is used to plan aircraft turnarounds and can be stored in airline computer systems for use in planning logistics support with respect to maintenance, replenishments and passenger consumables. ACARS reporting schedule ACARS uses the aircraft VHF radio system to transmit data between the aircraft and AOC facilities. The protocol for the information transmitted is detailed in an ARINC standard. The ACARS computer on the aircraft receives the ACARS encoded data after it is received and demodulated by the VHF radio system. The ACARS computer then decodes the data and provides a display to the flight crew. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 263 of 356 Airborne ACARS Components The airborne components of ACARS are Management Unit (MU), Control Unit (CU) and printer. ACARS block diagram The ACARS management unit controls the transmission and reception of air-to-ground and groundto-air messages through the VHF transceiver. It receives and sends digital messages to the VHF transceiver and contains circuits to control peripheral devices and generate a GMT (Greenwich Mean Time) clock used in recording event times and has conduct Built In Tests (BIT). The management unit uses aircraft sensors to identify events such as clearing the gate, being ready to taxi or takeoff or landing to trigger the collection of data from the control unit and various aircraft and avionics systems. The collected data collect is formatted into a digitally coded signal that will be transmitted to the ground by the VHF transceiver The control unit allows changing of operation modes and the flight crew to enter information into the data link system through an alphanumeric keyboard. The printer provides a hardcopy print-out of data collected by the management unit. Data that will be printed include uplinked messages that includes weather reports and dispatch messages. An uplink is the radio transmission path upward from the earth to the aircraft. A downlink is an air-to-ground transmission, while an uplink is a ground-to-air transmission. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 264 of 356 Satellite Communications Introduction to Satellite Communications A communications satellite is an artificial satellite that amplifies and relays radio telecommunications signals via a transponder. It creates a communication channel between a source transmitter and a receiver at different locations on earth. SATCOM system A UHF radio is installed in the aircraft to communicate with commercial satellites in orbit overhead. To date, it has been used primarily for telephone calls and ACARS data link principally for monitoring the status of the aircraft systems. The equipment currently available is very expensive; the antenna used with SATCOMM is a special type that must be installed on top of the aircraft. The high-gain system antenna (due to signal attenuation) can be used for highspeed data and voice communication. SATCOM can transmit voice and data from AIRCOM (ATC), ACARS, flight-crew, passenger telephone, telex, fax and internet. Some of the negative perceptions of satellite communications include: Transit delay time of approximately 0.25 seconds in all communications (voice and data) Lack of coverage at high latitudes High cost of airborne installations and high cost of the use of the link Size of the avionics package which excludes fitment on small and medium size aircraft. In the early 1980s, INMARSAT was launched, consisting of three geostationary satellites providing global coverage and a series of earth stations. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 265 of 356 In summary, the general perception of current satellite communications systems is that they are expensive, only suitable for low-density airspace and are only likely to be fitted to long-haul aircraft. This perception continues to favour the use of older HF communications and data systems. Passenger Communications Aircraft operators are now looking into offering novel value-added services for their passengers: email and internet access, on-demand video and more generally multi-media. Due to the increasing pressure on the existing VHF spectrum and limitations of current technology, satellite communications could play an important role in meeting passenger communications requirements. The satellite communication system provides a means to provide additional communications links to an aircraft (in addition to the VHF band), but installations are very expensive, take up significant space and weight (all the cabling to the passenger seats) and satellite time is expensive. Passenger communications include telephone, fax and e-mail options. As described, the radio link between aircraft and the ground is virtually unlimited in the type of data it can carry although full duplex operation requires a full suite of hardware for both the transmitter and receiver, and it is necessary to then use two frequencies to conduct a full duplex conversation. If there is a dedicated passenger communication system incorporated in the aircraft, data can be transmitted and received in the same way as communications described throughout this lesson. Installations require a significant amount of additional wiring and control boxes to provide connectivity to each passenger seat. Passenger communications When a call is placed, information is sent from the phone handset to a transceiver and then down a ground radio base station. From there, it is sent to the public telephone network. For satellite calls mainly over water, information is sent first to an orbiting satellite. From there, the calls are sent to a satellite earth station instead of a radio base station and onto the public telephone system. The frequency assigned to in-flight systems is unique, so it does not interfere with the plane’s navigation, communications or data processing equipment. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 266 of 356 Emergency Location Equipment Introduction to Emergency Location Equipment Emergency location equipment is used in aircraft for the transmission of emergency signals because of a forced or emergency landing. Types of emergency location equipment: Emergency Locater Beacons (ELBs)/Emergency Locator Transmitters (ELTs) Underwater Locater Beacons (ULBs). Emergency Locator Beacons/Transmitters Emergency Locator Beacons/Transmitters (ELBs/ELTs) transmit a distress signal that includes coded aircraft identification and its Global Positioning System (GPS) coordinates. The system was developed using a frequency of 406.025 Megahertz. This allows for the identification of false signals much more quickly and reduces response time to the crash site. COSPAS SARSAT system 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 267 of 356 An active beacon is detected by orbiting satellites which transmit a signal to search and rescue coordinators. An internationally utilised service provider ‘COSPAS-SARSAT’ is currently used in Australia to provide satellite-based ELT monitoring services. The ELT also emits a transmission on a frequency (121.5/243 MHz) which can be detected and homed in on by overflying aircraft. The homing signal is easily recognised and is modulated from 300 to 1600 Hz. The tone therefore starts as a low sound and increases to a higher pitch and then starts the cycle again. The distress signal operates on a line-of-sight basis and can be intercepted at approximately 100 miles range at 10 000 feet, given favorable conditions. A transmitter may be operated by the pilot from a switch in the cockpit or by an impact switch which is either integral to the unit or located at strategic points on the airframe. The ELT ELB must be installed as far aft as possible but in front of the tail surfaces since this area has been shown to remain intact in most airplane crashes and should be accessible from outside the aircraft to allow for manual activation and deactivation (if set off accidentally). The ELT/ELB will transmit for a minimum of 48 hours. Emergency locator transmitter One style of ELB that is contained in the life rafts is a small buoyant automatic transmitter with a water activated battery and a self-erecting antenna. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 268 of 356 Emergency locator beacon Underwater Locater Beacon Commercial passenger aircraft carry an emergency underwater locater beacon, or ULB, as part of the flight data recorder (FDR) and cockpit voice recorder (CVR). The flight data recorder ULB emits an emergency signal either above or below the water. Under water location beacons transmit on 37.5 kHz, which is a low frequency band. This lower frequency has better characteristics for underwater transmission. Underwater locator beacon The transmitted signals are a constant beeping, or something similar, and act as a homing signal for emergency services. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 269 of 356 Cockpit Voice Recorder Cockpit Voice Recorder (CVR) is a flight safety “black box” which is designed to monitor all signals transmitted and received as well as conversation and all other tones, aural warnings or noises in the cockpit area. The CVR picks up, amplifies and records on magnetic tape or digitally for a period of at least 30 minutes and is designed to be downloaded in the event of an accident to help find out the cause of the accident or other information that may assist in the investigation. The voice recorder cannot be played back on the aircraft. Due to the introduction of solid-state memory, it is now possible to have 2-hour CVRs with enhanced reliability and crash/fire survivability. The recorder is painted bright orange, or “rescue” orange, with white reflective stripes and is located in the same region as the emergency beacons in the aft fuselage area forward of the vertical fin. This part of the aircraft is most likely to survive in the event of an accident. The system consists of the following: Microphone Cockpit control panel Cockpit voice recorder unit with underwater location beacon. CVR System Components Microphone The microphone is for the input of all cockpit communication, tones and noises in the cockpit area. Microphone located in the overhead panel 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 270 of 356 The microphone can also be incorporated in the CVR control panel. CVR Control Panel CVR control panel Test Button This button provides a means of testing the performance of the CVR system by recording a test tone into the CVR memory or checking digital memory. Headphone The headphone jack allows audio checks of the CVR system, either by replaying tones recorded in memory during testing or monitoring audio inputs. Status Indicator An LED is used to indicate serviceability during tests on modern systems (usually red or green). Monitor (not shown above) Older systems sometimes provide a dial indicator used during system testing to show audio level and quality on playback. Erase Button 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 271 of 356 The erase button allows for the memory to be completely erased. Preconditions for erasure are designed to prevent in-flight erasure and to minimise inadvertent erasure during crash impact. All of the following conditions must be met for the memory to be erased: Weight on wheels Park brake set Erase button pressed for greater than a set time (between two and five seconds). Microphone A microphone may be inbuilt into the CVR Control Panel if it is in a suitable position to record cockpit area communication, tones and noises. Exploded view of CVR The Cockpit Voice Recorder (CVR) unit records four channels continuously and separately as follows: Channel 1 records the flight interphone and passenger address. Channel 2 records the output of the first officer’s audio panel. Channel 3 records the output from the captain’s audio panel. Channel 4 records all cockpit audio that is picked up by the cockpit area microphone located in the CVR panel. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 272 of 356 The system is powered from the most reliable source, normally the 115-V AC essential bus, and is operational as soon as the cockpit voice recorder circuit breaker is closed. Recorders are equipped with an Underwater Locator Beacon (ULB) to assist in locating the unit in the event of an overwater accident. 2023-01-18 B1-11f Turbine Aeroplane Aerodynamics, Structures and Systems CASA Part Part 66 - Training Materials Only Page 273 of 356