Comm Midterm
Most airliners have this many VHF transceivers
1
2
3
4
Modern aircraft
No longer use VHF-com, as SATCOM has made it obsolete
Use VHF strictly for voice communication
Use VHF to communicate with the ACARS
Are limited to one VHF transceiver each
For VHF, the PTT
Mutes the audio from the mic
Is not used
Switches the radio from receive to transmit
Activates the Power Transfer Takeoff
Splitting of VHF frequencies
Occurs when antenna coupling is not correctly calibrated
Allows for more frequency allocations
Prevents interference caused by the ionosphere
Is done in the VHF transceiver
For VHF, the audio control panel
Gives the pilot control over the volume
Only provides monitoring via headset
Is disabled
Provides digitization of the audio signal
Communications Systems
Move information
Are limited to providing audio only communication between the aircraft and the ground
Are all radio based
Do not include digital data transfer
The VHF transceiver
Contains its own voice recorder
Does not process audio, only RF
Sends audio to the cockpit voice recorder (CVR)
Will keep volume low until a specifically identified message is received
A VHF communication transceiver:
Requires two antennas, one for transmission, and another for reception
Requires an internal antenna to reduce drag
Requires only one antenna per transceiver because it does not transmit and receive at the same time
Does not require an antenna because it is only for internal communications
The VHF radio
Is a receiver
Is a transceiver
Is a transponder
Is a transmitter
The VHF transceiver is normally
In scan mode
In single sideband (USB) mode
In transmit mode
In receive mode
Indications for VHF
Include altitude if in Mode C
Are typically displayed on an HIS
Are typically displayed on an RMI
Are limited to frequency and selection indications on the control panel
ACARS communication
Is done by a dedicated VHF transceiver
Is controlled by the Selcal decoder
Is done by all VHF transceivers
Is done on the HF band
The VHF control panel
Includes a reset button to reactivate the Selcal scanning
Uses a switch or button to switch between two frequencies
Includes a decision height bug
Controls the volume of radio communications
VHF-Com
Is only used for non-critical communications due to its unreliability
Has been mostly replaced by GPS
Is also known as simply VHF
Is a special subset of the VHF Radio Frequency Band
VHF
Is strictly reserved for aviation use
Is used for long distance transoceanic travel
Takes advantage of radio waves following the contour of the earth
Is used by aviation, fire, police and taxi services
Ground maintenance on VHF
Requires the Selcal decoder
May be done by connections and indications on the transceiver
Is completely automated and built in
Is done strictly through the VHF control panel
The VHF control head
Is where station frequencies are selected
Indicates which VHF station is nearest the aircraft
Is where the volume of the received audio is controlled
Routes all VHF audio signals to where they are required
To be effective SATCOM antennas aboard aircraft
Are omnidirectional
Are usually mounted on the bottom of the fuselage
Must be mounted in pairs for transmission and reception
Must point to the satellite
The purpose of the HF antenna coupler is
To join the antenna to the AMU
To combine the transmitted and received signals
To match the antenna to the selected frequency electronically
To provide protection from EMF interference
HF communication
Are used only over ground stations
Are used for long distance communications
Uses direct line of sight transmission
Takes advantage of radio waves following the contour of the earth
Inmarsat
Consists of four satellites in geosynchronous orbit
Provides satellite communications at the poles
Controls 24 satellites in 6 earth orbits
Has been replaced by GPS
HF comms are unique in their requirement for
An antenna coupler
Noise cancelling circuitry
Internal antennas
A tone based on a four letter ID
One advantage of SATCOM
Is the fact that they do not require antennas
Is the ability to split frequencies
Is the precision of the positional fix
Is the capability for encryption
The USB selection on the HF control panel
Allows for transfer of data through the control panel via stick
Stores HF data for the entire flight
Is only used for ground maintenance
Selects single side band operation
SATCOM operates
By relaying communications between satellites to achieve long distance communication
By relaying information through satellites and ground stations
By comparing the signals of three satellites to provide a 2D positional fix
By interrogating a satellite and timing the response
Aircraft Earth System (AES)
Refers to the ground telephony component of SATCOM
Refers to the ground stations that communicate with aircraft via satellite
Refers to the onboard SATCOM equipment
Provides precise positional fixes in relation to the earth
SATCOM
Do not allow voice transmissions because it is a digital system
Is superior to preceding communications technology
Is limited due to the effect of sunspot activity on the ionosphere
Requires 24 satellites to provide a positional fix
SATCOM antennas
Require regular calibration to ensure data integrity
Tend to be large because of the large distances involved
Are more complex than most because of the requirement to aim the antenna at the satellite
Are simpler than most because they are omnidirectional
Audio signals required by the CVR and ACARS
Are provided by the AMU
Are routed by the audio control panel
Use SSB
Are digitized and encrypted
Selcal operates in the
UHF band
HF band
VHF band
HF and VHF band
Service interphone
Indicates that the interphone requires inspection, adjustment or maintenance
Provides communication between ground crew for maintenance activities
Allows the flight deck to communicate with flight attendants in flight
Is one advantage of using SATCOM
A key point for maintainers of communications systems
Is the high wear and tear on headsets
Is the tendency for these systems to require regular calibration
Is the memorization of all the frequency bands
Is the danger from RF when radios are transmitting
The AMU
Processes and encrypts all SATCOM transmissions
Monitors air movement to calculate airspeed
Processes and controls all audio signals required by the flight crew
Is the unit that modulates the amplitude of the carrier
The use of Selcal
Is only used for travelling over oceans
Extends the range of VHF communications
Is restricted to a 200 mile limit
Is restricted for emergency use only
The use of Selcal
Provides privacy over HF transmissions
Reduces the interference from selected frequencies
Provides precise positional fixes in 2D and 3D
Reduces the volume of HF reception until a code is received
Microphones
Increase the amplitude of audio on the flight deck
Convert audio energy into electrical energy
For aviation use must be carbon microphones
Reduce noise by limiting the modulation of the carrier
The Selcal decoder
Allows the pilot to select a 4 digit number to transmit to air traffic controllers
Distributes all audio within the service interphone system
Decrypts messages that have been scrambled for privacy or security
Allows for a code of 4 letters to be used to identify an aircraft uniquely
Selcal tones
Assure unique identification because the possible combinations are almost infinite
Are in the 3MHz to 30MHz range
Are four tones transmitted in mixed pairs
Alert the pilot of various errors in the system
The Selcal decoder
Is controlled by rotary switches in the cockpit
Is only operational in USB mode
Will cause an illuminated warning on the flight deck if it recognizes special tones
Has rotary switches with numbers on them
The flight deck speaker
May have audio routed to it as well as to headphones
Is only used when a headset fails
May not be used at the same time as headsets to avoid confusion
Is part of the IFE
Flight interphone
Allows communications between two aircraft in flight
Provides communication between flight crew onboard the aircraft
Provides communication between flight crew and ground crew
Provides cellphone service for passengers
The Audio Control Panel
Digitizes audio for distribution throughout the communications system
Controls how much modulation is applied to the audio signal
Provides command signals to the AMU
Provide encoding to the Selcal decoder
Communications systems
Are found on most aircraft
Are essential for safe flight
Do not include passenger entertainment systems
Are optional in VFR conditions
Selcal stands for
Selection Calculation
Select Calibration
Selective Calling
Selected Call Answering Limit
What is the "standard" test frequency for audio systems and devices?
100Hz
1KHz
15KHz
10MHz
What is the standard impedance of an aircraft headphone set?
8 Ohms
50 Ohms
150 Ohms
500 Ohms
What level of audio into an aviation headphone is considered normal?
10 micro Watts
20 milli Watts
1 Watt
20 Watts
What is used to convert voice into electrical signals for radio communication?
A flux capacitor
A microphone
An active transducer
A variable resonator
ELT stands for
Emergency Locator Transmitter
Emergency Location Transceiver
Extra Large Transmitter
Electronic LORAN Transmitter
Historically, many ELT failures were due to
Poor maintenance practices
Insufficient range capabilities
Poor design
Interference from the ionosphere
After an accident the ELT: -
Automatically senses a crash and sends out emergency radio signals
Receives information from ATC to aid in rescue attempts
Triggers a rescue when the signal stops transmitting
Uses GPS data to detect deceleration
Maintenance of ELT
Requires a yearly inspection and test
Is no longer necessary because of the use of integrated circuitry
Is governed by manufacturers specifications
Is limited to visual inspection of the antenna and LRU
ELT
Uses an accelerometer to detect rapid deceleration
Uses GPS data to detect rapid deceleration
Uses a barometric bellows to detect rapid deceleration
Uses data from the ADC to detect rapid deceleration
The 406 MHz ELT system
Can provide a fix within 1 to 3 miles of a downed aircraft
Use frequency matching to locate downed aircraft
Will soon be obsolete
Has completely replaced the 121.5 MHz system
The 406 MHz ELT system
Transmits about 5W of power
Transmits about 1/10W of power
Is strictly a receiver
Does not require satellites for operation
A Dongle system
Allows for an ELT to be used in different aircraft
Ensures the correct ELT is installed in an aircraft
Provides GPS data for tracking in an emergency
Keeps the battery charged in an ELT
The ELT system uses the following frequencies
121.5 MHz, 243 MHz, and 406 MHz
108.00 MHz to 395 MHz
121.5 MHz to 406 MHz
2 GHz to 4 GHz
What is the typical audio level on an aircraft speaker?
1 milli Watt
25 milli Watts
1 Watt
10 Watts
The typical impedance of an aircraft microphone set is: -
8 Ohms
50 Ohms
150 Ohms
500 Ohms
What is the frequency range of an aircraft 760 channel VHF communication radio
100Hz to 10KHz
2MHZ to 30MHz
118.00MHz to 135.975MHz
118.00MHz to 136.975MHz
When transmitting a call on an aviation radio, what is said second?
"This is"
"Testing testing"
The name and type of the station being called
Your call sign
When transmitting a call on an aviation radio, what is said first?
"This is"
"Testing testing"
The name and type of the station being called
Your call sign
What is the spoken word for urgency?
Help
Mayday
Urgent
Pan Pan
"Repeat" is not an acceptable word in communication. Which word has the same meaning and is acceptable?
Come back now
Once again
Read over
Say again
In the phonetic alphabet used in aviation, what is the spoken word for the letter
"A"
Albert
Alpha
Able
Apple
Troubleshooting is
A systematic approach to problem solving
Running BIT tests to find a problem
Replacing components to fix a snag
Using a multimeter to measure resistance
Troubleshooting
Is not strictly an avionics technician responsibility
Applies only to electronic systems
Is unique to aviation
Is no longer required because of computerized systems
The swap components method of troubleshooting
Is one of many methods
Is the best method
Is not a true method of troubleshooting
Is the cheapest method of troubleshooting
Troubleshooting involves
Applying what you know to a problem in an organized way
Informing the pilot of the steps taken
Programming test equipment
Reducing costs by reducing weight
Gather and Evaluate Information
Is the first step in troubleshooting
Is done away from the aircraft
Is not required
Is optional if you have test equipment
Two key foundational sources of information are
Training/Education and Manuals/Textbooks
Test equipment and observation
Pilots and supervisors
EFIS and DME
Symptoms
Help to determine the nature of a problem
Only appear when a piece of equipment has completely failed
Are invisible signs of malfunction
Require test equipment to measure
Experience
Shortens the troubleshooting process
Means that you don't need to troubleshoot
Usually results in fewer snags
Leads to complacence
Questions
Should be asked to narrow down possible causes of the problem
Indicate a lack of system knowledge
Are of limited usefulness in troubleshooting
Are only useful if you have access to the pilot
GeoSAR and LeoSAR
Use frequency matching to locate downed aircraft
Both use geosynchronous orbits
Use Doppler effect technology to locate downed aircraft
Are both low earth orbit satellite systems
Aircraft Registration
All of the above
Is predicted to reduce false distress alarms by up to 70%
Includes contact numbers in case of emergency
Involves transmitting unique identifiers along with the distress signal
Cospas and SARSAT
Are primarily used for telecommunications
Have greatly increased the rate of interception of ELT distress signals
Are optional components of ELT systems
Are primarily used for SAR
ELT Antennae
Are usually mounted on the top of the aircraft
Are usually mounted on the bottom of the aircraft
Are not necessary with the 406 MHz system
Are usually a whip antenna on faster aircraft
Overtightening fasteners
Is prevented with modern hardware racks
Results in a more secure installation
Can be reduced by undertorquing all mounting hardware
Is a problem no matter the design of the mounting hardware
New avionics equipment installations
Usually do not require any changes to existing structures or equipment
Are at the discretion of the AME alone
Are prohibited on aircraft manufactured after 2010
May require modifications to the aircraft itself
For equipment labelled with ESD warnings
The technician should be at the same voltage potential as the ground on the equipment
Only co-axial cable may be used to connect equipment
Electrical soldering irons are not permitted
The technician should seek an engineering disposition before installation
Because of the risks of contamination and moisture
Most avionics equipment is installed in the cockpit or passenger area
Only co-axial cable is used on avionics equipment
Some equipment is designed to withstand extreme environmental conditions
Avionics equipment is all waterproofed
When a cooling kit is available
The manufacturer is responsible for inspections after installation
Manufacturers' recommendations and specifications are optional
Manufacturers' recommendations and specifications must be followed
Use less ducting to reduce weight
Equipment cooling
Is usually accomplished with refrigeration units in larger aircraft
Is designed into larger aircraft
Is not necessary for GA aircraft
Is not normally an AME responsibility
Equipment cooling
Can be done with any sort of fan
Is not necessary for GA aircraft
Is not standardized in GA aircraft
Is standardized for GA aircraft
Keyways on multipin connectors
Prevent mismatching of pins
Provide security against theft or tampering
Ensure the correct torque on installation
Are only required on CommSec equipment
Avionics equipment in tight spaces
Are subject to more vibration
Increases need for cooling measures
Often interferes electrically with each other
Requires extra bonding to reduce stray voltages
Heat issues
Do not apply to equipment in avionics bays with cooling
Are no longer a problem with modern avionics
Do not apply to GA aircraft
Are a primary cause of avionics failures
Avionics equipment installation requires careful consideration
Unless the aircraft is sufficiently modern
No matter the size of the aircraft
Which is the sole responsibility of avionics technicians
Except for GA aircraft
The physical security of mounted equipment
Is a good thing to check first in troubleshooting
Is rarely a cause for faults
Only matters to flight safety when installed in the cockpit
Requires modern adhesives
Avionics equipment is subject to motion issues
Because motion causes electrical anomalies
Because it is built less strong than automotive components
Because an aircraft moves in many dimensions
Because of special sensors in the equipment
Contamination and moisture
Usually pose a problem in passenger areas
Are rarely a problem in modern aircraft
Are rarely problematic with modern semiconductors
Are particularly troublesome in low areas of the aircraft
Bonding
Provides moisture protection for avionics equipment
Puts all equipment at a common ground potential
Is the Technical Service Order which permits the installation of avionics systems
Prevents the loosening of fasteners
Bonding
Cannot be electrically verified with a visual inspection
Replaces jack screws and set screws
Prevents the loosening of fasteners
Provides moisture protection for avionics equipment
Your first choice when troubleshooting
Is usually the headset
Should be what is easiest, cheapest and most probable
Should be to replace transceivers
Should be continuity checks
Your first choice when troubleshooting
Is usually the headset
Should be what is easiest, cheapest and most probable
Should be to replace transceivers
Should be continuity checks
Your hypothesis will be better if
You use test equipment
You have more knowledge or experience
You do a functional check
It is based on the half-split method
Testing a hypothesis
Is carrying out the proposal of the hypothesis
May only be done by someone who has an AME licence
Will solve the problem
Is optional
The best troubleshooting method
Is to swap components
Is the half-split method
Is to form a hypothesis
Is situational
Once a problem is solved
There are several steps to finish the job
No test equipment is required
You should test your hypothesis
Operational checks are no longer required
In regards to troubleshooting
Experience does not matter
It may only be done by someone who has an AME licence
There is only one correct approach
There may be several correct approaches
Forming a hypothesis
Is done before troubleshooting begins
Is optional if you have test equipment
Is only necessary if you need wiring diagrams
Is the second step in Symptomological Analysis
Testing a hypothesis
Is the final step in the Symptomological Analysis
Is the end of the troubleshooting process
Requires specialized equipment
Is a step usually skipped by experts
Sources of information
Include your theory classes
Include test equipment manuals
Include pilot descriptions of problems
All of the above
Testing a hypothesis
Is only necessary if you use test equipment
Is the third step in Symptomological Analysis
Is optional if you have test equipment
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