11.05.2 Communications Flashcards
What are the 3 communication groups?
- Aircraft communications
- Radio communications
- Accident investigation
What are AC communication systems?
- Interphone
- Passenger address
What are radio communication systems?
- VHF
- HF
- Satcom
- ACARS
What are accident investigation systems?
- Cockpit voice recorder
- Emergency locator transmitter
- FDR
What are 2 requirements of communication?
- Information (Audio signal)
- Carrier (RF signal)
What are frequency bands?
- HF - 3MHz to 30mHz (ADF and public radio stations)
- VHF - 30MHz to 300MHz (distance upto 200nm, VOR, ILS)
- UHF - 300MHz to 3GHz (military comms, DME, ATC and GPS)
How do you work out wavelength?
T = 1/f
Two types of wave propagation?
- Skywave
- Groundwave
Which frequencies use each type of wave propagation?
- High frequency - Skywave
- Low frequency - Groundwave
How if HF wave propagated?
Reflected by ionosphere
What affects HF reception quality?
Time of day and frequency selected
What are two types of modulation?
- Amplitude
- Frequency
What are audio system components?
- Microphones
- Speakers
What does microphone do?
Converts acoustic to electrical
What does a speaker do?
Converts electrical to acoustic
What are three types of microphone?
- Area
- Hand held
- Integrated
What are three types of speaker?
- Loudspeakers
- Small loudspeakers
- Cabin loudspeakers
What are radio system components?
Antenna, transmitter, receiver
What is a combined transmitter receiver called?
Transceiver
What are three transmitter components?
- Oscillator
- Modulator
- Power amp
What does an oscillator do?
Generates RF carrier frequency
What does a modulator do?
Couples audio signal to carrier in either FM or AM
What does a power amp do?
Generates power to TX
What is normal power output for a VHF system?
25 W
What are three receiver components?
- Tuning circuit
- Demodulator
- audio amp
What length makes antenna most effective?
1/4 lamda
What is length of antenna for 150MHz?
0.5m
How can antenna be made smaller but still remain effective?
Electronic components
Wth HF frequency range of 2MHz to 30MHz, what is range of antenna length?
2.5m to 37.5m
How is HF antenna length varied?
Antenna coupler
What are connections between transceivers and antennae called?
RF lines
What are two types of RF lines?
- Coax
- Waveguide
Who should handle RF lines?
Only traiend personnel
What can disturb RF signal in RF lines?
Deformations or water contamination
What do static dischargers prevent?
Damage to electronic circuits and radio reception interferecne
What does audio management (AMU) do?
Manages all audio signals transfera relevant signals to CVR
Which crew members have an audio control panel?
All
Where are pilots and copilots audio control panels (ACPs) located?
Centre pedestal
Which microphone has priority, oxygen mask or boomset?
Oxygen mask
How many systems can be set to TX simultaneously?
Just one
How can you monitor transmitted audio?
Side tone
Which systems are Rx selectable only?
Nav systems
What does V position on ACP select?
only voice information
What does R position of ACP select?
Range identification code
What does B position of ACP select?
Both audio signals
How many RT positions are there on ACP?
3
What does centre RT position select?
Rx only
What does up RT position select?
Tx
What does down position RT select and how does this affect the microphones?
Interphone mics on permanently
What does comms transfer switch on overhead panel do?
Transfers comms to third crew member if fault
How does does mechanic tell pilot he wants to communicate with him?
Presses call button near jack plug
How does the mechanic wanting to communicate with the pilot display to pilot?
Illuminated mech light on ACP
Why are service interphone jacks only connected on ground?
Situated in dirty areas so noisy
How are service interphone jacks disconnected in the air?
Ground/air switch
How does the system prevent two signals being broadcast on the system at the same time
Passenger address power amp prioritises
What are PA signal priorities?
- 1 Pilot
- 2 FO
- 3 Cabin crew
- 4 pre recorded
- 5 boarding music
When does PA amp output increase?
- Engine start
- Oxygen mask deployment
How is PA amp output increase triggered?
- Engine oil pressure
- 14000ft cabin pressure switch
What is CVR used for?
Evaluation of incidents or accidents
What are two types of CVR and how long do they record for?
- Analogue 30 mins
- Solid state 120 mins
Where is the CVR normally located?
tail compartment
How many inputs are there to the CVR?
4 inputs
When does CVR recording start?
First engine start or when AC in flight at latest
When does CVR recording stop?
5 mins after shutdown or last engine on ground
When is is possible to erase CVR tape?
AC on ground with parking brake set
When operating CVR test, what are the indications?
- Needle in green or test pass status
- Records test signal on four channels
What is VHF used for?
Short distance voice and data
What is VHF frequency range?
118MHz to 136.975 MHz
What is VHF international emergency frequency?
121.5 MHz
What is norml VHF channel spacing and how many channels does that provide?
25KHz and 760 channels
How many VHF systems are there?
3
How is VHF comms controlled?
RMP
What must you do before transmitting on radio system?
Listen to ensure no-one is talking
What does missing side-tone during VHF transmission indicate?
Tx system failure
How many windows on a radio maintenance panel?
two
What are the two windows on a radio maintenance panel?
active and standby
What shows in RMP active window when ACARS is active?
ACARS or DATA
What steps are required for VHF communication to ground?
- ACP system selected
- RMP correct system selected and frequency
- Frequency in active window
- Listen to ground for other transmission
What is HF used for?
Long distance comms
What determines reception quality in HF?
Time of day and selected frequency
Where is HF antenna usually located?
Leading edge of vertical stab
What is HF frequency range?
2MHz to 30MHz
What is HF power output?
200w to 400w
What modes can be selected by AM button?
AM and single side band (SSB)
When does antenna tuning take place?
Short press of PTT
What tuning indications are there?
- Light
- 1Khz tone
What is ACARS used for?
Message and data transfer between AC and ground
Which system does ACARS normally use for transmission?
VHF 3
What is aircraft to ground transmission called?
Downlink
Are ACARS reports manual or automatic?
Both
What does he ACARS management unit (MU) do?
Connects ACARS to other AC systems
When ACARS uses Satcom because VHF station unavailable, where does it get its position from?
Flight management computer
How is ACARS management unit software updated?
Data loader
How is ACARS controlled?
Through the MCDU
What are the 3 components of SATCOM?
- Satellites
- AC stations
- Ground earth stations
What does satcom provide that other systems don’t?
Multiple connections and 2 way connections for phone calls etc
How many satellites does satcom use?
4
What is the coverage of satcom satellites?
75 degrees north to 75 degrees south
How many satcom stations are there worldwide?
255
What are SATCOM system components?
- SDU
- RFU
- HPA
- LNA/Dip,
- Beam Steering Unit and antenna
What does SDU do in satcom?
Controls all connections to AC systems has satellite locations and frequencies
How many antennas does SATCOM use?
1 top mounted or two side mounted
What advantage of low gain antenna over high gain?
- No beam steering unit
- No AC position data required
What must you ensure when using SATCOM on ground
no personnel of metal objects near antenna
What is ELT used for?
Search and rescue/find aircraft
What are two types of ELT?
Fixed
portable
What are two international emergency frequencies?
121.5Mhz, 243 Mhz
How far can international emergency frequencies be received?
Up to 200 nm
How long does ELT internal battery last?
at least 48 hours
How is a buoyant type of ELT activated
Contact with water
How is a fixed ELT activated?
Excess of 5g longitudinal axis or set manually
