Equipment Exam Flashcards
What types of waves are radio waves?
Sine Waves
What are the advantages of using FM radio?
- Resilience to noise: Any signal level variations will not affect the audio output
- Easy to apply modulation at a low power No boosting of the amplitude required
- Use of efficient RF amplifiers This means that for a given power output, less battery power is required and this makes the use of FM more viable for portable two-way radio applications
What do FM and AM stand for with regards to RT?
FM= Frequency Modulation
AM= Amplitude Modulation
What are the advantages of AM radio?
Stronger stations can override weaker or interfering stations, and don’t suffer from a capture effect found in FM.
- If a pilot is transmitting (Tx), a control tower can “talk over” that Tx and other aircraft will hear a somewhat garbled mixture of both Tx’s rather than just one or the other.
- A heterodyne (Squeal) will be heard, even if both Tx’s are received with identical signal strength. No such indication of blockage would be evident in an FM system
What is the frequency range and Wavelength of a VHF signal?
-30-300MHz
10m-1m
What is the frequency range and wavelength of a UHF signal?
300MHz-3GHz
1m-10cm
What is the amplitude of a radio wave?
The maximum displacement or value attained by the wave from it’s mean value during a cycle.
What is the wavelength of a radio wave?
The distance in metres or part of a metre between corresponding points in consecutive waves
What is the frequency of a radio wave?
The rate of repetition of the cycle in one second (oscillation). One cycle per second would be 1 hertz.
Ie how many oscillations/sec
What is velocity with regards to radio waves?
The speed in a given direction.
velocity= frequency x wavelength
What is a carrier wave?
A wave which carries the audio feed by modulating the audio wave and carrier wave together.
A carrier wave is produced by an oscillator
What type of modulation is used in Air Traffic and why?
AM
Due to the ability to overpower weaker radio signals.
Also produces a heterodyne when two or more stations are transmitting at once so that everyone knows when two or more stations are trying to transmit.
What is the ideal length of an aerial?
The same length as the wavelength of the wave being transmitted.
Can transmit proportions of the wave by being either half or a quarter of the wavelength instead to create more practicable lengths.
What is an amplifier?
It amplifies the strength of the received signal, needs a noise gate to prevent it from amplifying any static noise as well.
What is attenuation
The reduction in strength of a radio wave with time from the point of transmission.
As a wave attenuates the amplitude of the wave will decrease, the frequency and wavelength remain unchanged.
Longer wavelengths (lower frequencies) are less affected owing to interacting with less particles for a given distance and vice versa.
What are the wave-bands of the radio?
Freq Band. Spectrum of frequency. Wavelength
Very Low (VLF) 3-30KHz. 100-10km
Low (LF). 30-300KHz. 10-1km
Medium (MF). 300KHz-3MHz. 1km-100m
High (HF). 3-30MHz. 100-10m
Very High (VHF). 30-300MHz. 10-1m
Ultra High (UHF). 300MHz-3GHz. 1m-10cm
Super High (SHF). 3-30GHz. 10-1cm
Extremely High (EHF). 30-300GHz. 1cm-1mm
What is the frequency band for VLF and what is it used for?
3KHz-30KHz
100km-10km
Long range communications
What is the frequency band for LF and what is it used for?
30-300KHz
10km-1km
Reliable long range communications
Requires large aerials and high transmitter power
What is the frequency band for MF and what is it used for?
300KHz-3MHz
1km-100m
Used for reliable long range communications.
Very congested waveband
Used for NDB’s
What is the frequency band and wavelength for HF and what is it used for?
3-30MHz
100m-10m
Long range communications by day and night limited by diurnal (day and night) and seasonal variation of ionosphere.
RTF communications.
What is the frequency band and wavelength for VHF and what is it used for?
30-300MHz
10m-1m
Line of sight communications
Small aerial and transmitter power
Used for main ATC RTF frequencies
Free from static interference
Easy to suppress aircraft signals
Prone to ducting
VOR, VDF
Surveillance Radar
What is the waveband and wavelength for UHF and what is it used for?
300MHz-3GHz
1m-10cm
Line of sight comms
Used for surface communications with vehicles
Free from static interference
Prone to ducting
Used for ILS (DME element), DME’s, surveillance RADAR
What are the wave bands and wavelengths of SHF and EHF frequencies and what are they used for?
SHF is 3-30GHz 10cm-1cm
EHF is 30-300GHz 1cm-1mm
Short range communications
Precision, surveillance and airborne weather radar.
What is antenna shadowing?
When the transmitter aerial is shadowed from the receiver as the radio wave travels in a straight line so may be blocked by the curvature of the earth for example.
What happens when a wave is ducting?
It is bouncing off of a temperature inversion or under certain atmospheric conditions which may reflect VHF, UHF and SHF waves back to the ground and they will bounce around in this ‘duct’
What is propagation with reference to radio waves?
Similar to ducting but with low frequencies bending around objects that would normally shadow the signal. Can be heard a great distance from the source as the low frequencies mean lower attentuation.
What do we use RADAR for in Air Traffic Control?
Area Control
Approach Control
Aerodrome Control
- Air; traffic integration, approach monitoring
- Ground; Runway protection, monitoring ground hazards
How does RADAR work?
By calculating the time taken for a signal of a known speed to be recevied as an echo we can calculate the distance using the following equation.
Distance= (speed x time)/2
What does RADAR stand for?
Radio Detection And Ranging.
What are the two types of RADAR used in ATC?
Primary (PSR)
Secondary (SSR)
How does Primary RADAR work?
By sending out a pulse of electromagnetic energy and waiting for a reflection, as the speed of the wave is known (c) then the distance can be calculated easily.
distance= (speed x time)/2
This tells us how far away the object is and by combining this with the information about which way the RADAR was facing when the signal was received we can determine the position of an aircraft as well.
What waveband does RADAR operate in?
1mm-100cm
This is the same part of the electromagnetic spectrum as microwaves.
What wavelength is used for SMR?
2-3cm
What wavelength is used for Approach Radar?
3-10cm
What wavelength is used for Area RADAR?
23-50cm
What are PE’s?
Permanent Echoes
These are the position indications given by permanent objects in the area of operation of a RADAR, they can be used to check that the RADAR is still correctly aligned.
What is clutter and how is it formed?
Unwanted returns on a RADAR screen, these can be caused by ground, buildings, or weather (the rain droplets in clouds is what causes clouds to reflect RADAR)
What is a PSR blip?
The visual indication, in non symbolic form, on a situation display of an aircraft obtained by PSR.
What is a position indication?
A generic term for the visual indication, in non symbolic and/or symbolic form, on a situation display of the position of an aircraft, aerodrome, vehicle or other object.
What is a position symbol?
A visual indication in symbolic form, on a situation display, of the position of an aircraft, aerodrome vehicle or other object obtained after automatic processing of positional data derived from the source.
What is RADAR contact?
The situation which exists when the RADAR position of a particular aircraft is seen and identified on a situation display.
What is RADAR control?
Term used to indicate that RADAR-derived information is employed directly in the provision of ATC service.
What is a situation display
The screen. Displays the electronic information regarding position and movement of aircraft.
What are the three basic blocks of RADAR operation?
Transmission
Reception
Display
What is a duplexer?
Is a transceiver that can transmit and receive, but only does one or the other at a time.
What is the trigger unit?
It is the device that creates the pulses which are modulated by the modulator into the pulses that the RADAR actually sends out.
What is the unambigious range of a RADAR?
This is the maximum technical range from which a target echo or transponder response can be received. This determines the PRI.
What is the PRI of a RADAR?
The Pulse Repetition Interval
The interval between pulses necessary to receive a return from the unambigious range. ie how long would be needed between pulse replies to receive a signal from the RADARs maximum range.
This determines the PRF
What is the PRF?
The pulse repetition frequency
The number of pulses that can be trasmitted in a second.
Higher PRF the greater the clarity of the position return displayed as you get more ‘hits’ on it.
What is SSR?
Secondary Surveillance RADAR
RADAR that works by the sending an interrogation signal to the aircraft transponder which sends a reply to the station. The distance is calculated by the time taken for the response to tbe received and the direction is taken from the direction the RADAR is facing. The response can also contain height and identity information as well.
What are the frequencies for SSR?
The ground stations transmit the interrogation signal on 1030MHz
Aircraft transponder sends the reply on 1090MHz
What is the wavelength for SSR?
30cm
How does the interrogater actually interrogate the Transponder?
By sending a pair of pulses which are seperated by a certain time interval between each pulse.
8.5µs for Mode A
21µs for Mode C
The aircraft will then recognise this and send back the appropriate information.
How many binary bits are there in Mode A?
12 bits
This limits the possible amount of codes to 4096 discrete codes
How many Mode A codes are there?
4096
What are the different types of squawk codes?
- Discrete codes- Those assigned to individual aircraft
- Non Discrete- Single codes issued to numerous aircraft ie conspicuity
- Special codes- Applied to aircraft on certain occassions
What are ORCAM codes?
Originating Region Code Assignment Method
Codes are assigned depending on what participating area they come from.
It is designed to reduce RTF and cockpit work-load by allocating an SSR code which can be retained from take-off to touchdown.
What are the emergency special codes?
7500- Hijack/unlawful interference
7600- Radio Failure
7700- A/C emergency
What are conspicuity codes?
Codes assigned to individual positions to identify aircraft being controlled by a particular unit to another unit. Helps in coordinating between units.
How many bits are there for Mode C?
11
this is because the numbers 8 and 9 are now required.
What is garbling?
Position indications and position symbols may overlap making them impossible to read or even causing the mode A codes to be incorrectly displayed.
Is conteracted by a de-garbler
What is fruiting?
False Replies Unsynchronised in Time
Falses responses being received.
Removed by a de-fruiter.
What effect does shortening the wavelength have on the RADARS coverage?
For a given aerial height this will improve the low coverage but decrease the higher coverage
What effect does lengthening the wavelength have on the RADARS coverage?
For a given aerial height it increases the higher coverage but decreases the lower coverage.
What type of Radiation pattern do ATC use and why?
Cosecant Squared
Because it saves power.
What is a unit coverage diagram?
The diagram which shows the actual coverage of the RADAR system.
Operational RADAR procedures are determined from this.
What effect will shortening the wavelength have with regards to attenuation and atmospheric effect?
It will cause it to attentuate faster and increase the atmospheric effect on the coverage. Due to increased interaction with molecules in the air.
How much power does a primary RADAR need?
Enough, allowing for attentuation, so that the RADAR can detect an echo from an aircraft at maximum range.
What is the pulse length?
The length of the pulse sent out by the RADAR
This must be short enough to allow replies from previous pulses to be received and for the RADAR to enter receiving mode before transmitting again.
This therefore determines the RADARs minimum range.
What is circular polarisation?
The thing that overcomes weather clutter.
What is an MTI?
Moving Target Indicator
This makes the RADAR screen display only those targets which are moving as the rest are filtered out. This helps to reduce PE’s and clutter.
However this relies on radial movement of the aircraft between pulses otherwise it appear stationary.
What is Tangential Fading?
If the aircraft is moving 90° to the RADAR beam tangentially the aircraft will not move radially and will therefore be filtered out by the MTI.
What is blind velocity fading?
When the aircrafts radial distance changes by half a wavelength during one pulse occurence, can also happen when the distance is a multiple of half of the wavelength. It causes the blip to cancel itself.
This normally happens when the aircraft is heading directly away or to the RADAR head.
What are the methods whereby information can be transferred from RADAR sites not located at the aerodrome?
- Coaxial cables (expensive and limited to short distances)
- Radio link (operates in UHF to SHF frequencies, needs repeater stations if going a long distance)
- Telephone link
- Fibre optics
What is multi-RADAR processing?
Processing of information by multiple RADAR heads.
The airspace is divided into grids 16x16nm forming columns or air going upwards called RADAR sort boxes. This box will be covered by multiple RADAR’s, the one offering the best signal will be the primary with others being the supplementary and the reserve meaning that even if one fails there are always back-ups.
The pictures from these RADARs are pieced together like a mosiac.
What is a plot extractor?
Its a device that changes analogue signals from PSR and SSR into digital signals. Allowing further data processing such as Mode A squawks being replaced with the actual Callsign.
How is Groundspeed calculated by a RADAR?
Once in a digital signal the RADAR can process the past movements of the indication and use these to calculate groundspeed.
What is track fusion process?
Data from several RADARs combined in all parts of the screen, it determines an average position from all the sources to give a more accurate picture of aircraft positions.
What information can be displayed on a Video Map?
- Significant points- nav aids, holding points etc
- Final Approach Tracks
- Airspace restrictions
- Controlled Airspace Boundaries
- Coastlines and rivers
- FIR and national boundaries
- Lat and Long
What is mode S?
Selected
It is a form of SSR that selectively interrogates aircraft instead of just generally interrogating them all. Individual interrogations reduces garbling and Fruiting.
Allows each aircraft to have its own unique code.
What frequency band is Mode S?
1030-1090MHz same as all other SSR.
How many bits does Mode S use to assign codes and how many codes does this allow?
24 bits
16.75 million.
What are the phases for Mode S?
- Operation Acquisition Phase- interrogator tracks conventional responders looking for new Mode S transponders and retains in its memory the individual addersses for the next phase.
- Addressed survelliance phase- Mode S a/c individually interrogated for ATC identification, altitude, and other data.
What is the CPA?
The closest point of approach.
The Mode S transponders TCAS procduces a CPA which includes a two level proximity warning, produced by talking directly with other aircrafts transponders.
When using Mode S how is information passed between the ground and the aircraft?
It is uplinked from the ground
Downlinked from the aircraft.
What information does elementary Mode S provide?
- Identification
- Squawk
- Level
- Position
What information is provided by enhanced Mode S?
- Position
- Identifiction
- Flight level
- Selected altitude
- IAS
- Ground speed
- Mag heading
- RoC RoD
What is ADS-B?
Automatic Dependent Surveillance Broadcast
Works like a passive radar receiving signals from onboard equipment from the a/c. A/C deduces its own position and passes down to the ground station. Can also be used as a downlink to send and receive messages from the a/c or ground, much like CPDLC except it has less pilot input.
Can allow non-procedural approach procedures in area of little or no RADAR coverage. Can also be used to augument RADAR coverage in areas of RADAR shadowing, eg hills/ mountains near an airport.
• ADS-B broadcasts; horizontal position, vertical position, and velocity; as well as other information.
• Can be used by aircraft or vehicles.
- Also can be received by ground facilities.
- Enables a passive system to monitor, uniquely identify, and track all targets in range.
- Suitable for ground, and airborne application. (For sole-source surveillance)
- Is reliant on ALL users providing accurate information ALL of the time.
Automatic- Always on-No operator intervention
Dependent- The system relies upon very accurate GNSS navigation data.
Surveillance- Provides aircraft position, heading, speed, altitude, identification, and other data.
Broadcast- No interrogation required. Data is broadcast to any ADS-B station.
- It uses a downlink and messages can also be sent from the antenna to the a/c
- NATS are currently investigating the potential of using this for separation purposes.*
What are the advantages of ADS-B?
- Relatively inexpensive, 0.01% the cost of equivalent RADAR
- Smaller Power requirements and footprint, allows installation in remote areas.
- Comms links are satellite and Microwave
What is MLAT?
Multilateration
Very similar to ADS-B.
MLAT antennae on the ground receive position reports from a/c via Mode S or ADS-B broadcast, the exact position is then worked out using TDOA (time diffrence of arrival) which uses the difference in receipt times of the signal between different antennae to work out the position.
Displays on the Situation display in the same way as ADS-B
Short range ones can be used to augument SMR, much cheaper and easier to maintain than SMR also more accurate and faster. Need several antennae to achieve necessary coverage.
Wide area MLAT can be used to cover larger volumes of airspace. In augmentation with RADAR (which is sometimes impractical).
Who can use ADS-B?
Aircraft and vehicles, must be equipped with transponders to be visible though.
What frequency does ADS-B use?
1090MHz
same as SSR
What are the three message types of ADS-B?
- Position
- Airborne Velocity
- Aircraft Identity
What is the maximum accuracy category of ADS-B
7.5m
What is the minimum accuracy category?
>20nm
What is ADS-C?
Automatic Dependent Survelliance Contract
A ‘contract’ is established between the aircraft and the ground station. This contract establishes what reports the aircraft must make to the ground station and when they must be made. The ATSU will have to establish what type of contract is to be made before the ADS-C reports will be sent from the aircraft.
What are the type of ADS-C reports?
- Periodic contract
- Demand contract- ATC will demand a report from the a/c now, such as a level report.
- Event contract- Aircraft is told to make a report when doing a certain thing eg vacating a certain flight level
- Mayday contract- only the pilot can cancel this one.
What are the advantages of SSR?
Advantages
- Less power for similar range
- No ground or weather clutter
- Display and identification of aircraft simplified
- Level Info
- Emergency Squawk Codes
- Can be equipped with safety nets (STCA etc)
Disadvantages
- All a/c need a transponder
- No weather returns
- Fruit
- Garbling of TDB’s
- Fading
- No permanent echoes for calibration
- Cant be used for controlling on its own (except during PSR failure) owing to needing a/c to squawk so needs PSR coverage too.
What is an STCA?
Short Term Conflict (STCA) – visual and (sometimes) aural warnings if potential aircraft conflicts detected.
• (Medium Term Conflict detection (MTCD) gives much earlier notice of conflicts and is used in ACCs, but is considered a planning tool, not a safety net)
What is MSAW?
Minimum Safe Altitude Warning (MSAW) – visual and (sometimes) aural warning if radar system detects aircraft below minimum safe altitude, based on SSR transponder altitude readouts
What is RIMCAS?
Runway Incursion Monitor and Collision Avoidance System (RIMCAS)
- Fitted to some surface movement surveillance systems
- Provides Tower controllers with audio and visual warnings of potential conflictions on runways
- (PSR and SSR returns can both trigger RIMCAS) )
What is an AMA/ AFDAS?
Approach Monitoring Aid
- Also known as Approach Funnel Deviation Alerting System (AFDAS)
- Automatically monitors aircraft on final approach and provides visual and aural alert to Tower controller of any significant lateral or vertical deviation from final approach track or glide path
What is CAIT?
Controlled Airspace Infringement Tool (CAIT)
- Radar system monitors squawks and mode C readouts to alert radar controller to any unauthorised entries into controlled airspace
- A version of CAIT can also detect non squawking aircraft entering CAS which extends upwards from the surface with no upper limit e.g. the London CTR, above which lies the London TMA up to FL 195 and then class C airspace above that.
Who can use MLAT?
Aircraft and vehicles, must be equipped with transponders to be visible though.
What are the disadvantages of SSR?
Disadvantages
- All a/c need a transponder
- No weather returns
- Fruit
- Garbling of TDB’s
- Fading
- No permanent echoes for calibration
- Cant be used for controlling on its own (except during PSR failure) owing to needing a/c to squawk so needs PSR coverage too.
What are the advantages of PSR?
- Self contained
- Independent operation-solely provides identification and fix of the aircraft
- Non-reliant- A/C dont need a transponder
- You get PE’s, which can be used to calibrated
- Weather Information
What are the disadvantages of PSR?
- No level info
- Identification requires a much higher workload
- Weather clutter
- PE’s can be obscuring
- Range depends on transmitter power, target size and properties
- No emergency indicator
What is the ideal RADAR setup for a live traffic environment?
Having both secondary and primary RADAR
This is so you can over come the disadvantages of both.
Can PSR be used on its own for identification and control of aircraft?
Yes
Can SSR be used on its own to identify and control aircraft?
No, it can only be used for the minimum time necessary to establish other forms of separation.
What is an FMS?
Flight Management System
The overall computerised electronics system on the aircraft used to assist in nav, flight planning, and aircraft control.
What are the three major components of an FMS?
- FMC- Flight Management Computer
- AFS- Auto Flight System
- Navigation.
What are the primary functions of an FMC?
To compute real time nav data, and show it as a moving map for the pilots, this map will contain SIDs/STARS etc. It can also calculate the performance data based on weight, altitude etc.
What is CPDLC?
Controller Pilot Datalink Communications
A data link that allows for the transfer of text messages between ATC and the pilot, these messages can be uplinked straight to the FMS making them automatic.
Improves communication capabilities in oceanic areas.
What are the benefits of CPDLC?
- Allows flight crew to print messages, less ambiguity especially for foreign pilots
- Allows auto uplink of messages straight into the FMS
- Allows crews to downlink complex route clearances and requests.
What is ADS emergency mode?
A mode selected by the pilot that informs ATC that the aircraft is experiencing an emergency, including changing the squawk automatically.
Only the crew can initiate and turn this off.
Does a clearance delivered by CPDLC require a readback?
No, the only ‘readback’ is a wilco message sent by CPDLC.
How can the flight crew select down-link emergency mode?
- The sending of a CPDLC MAYDAY message automatically places the CPDLC and ADS into emergency mode.
- The crew can also manually select ADS emergency mode, independent of the CPDLC.
Who initiates and turns off the emergency down-link mode?
The flight crew only.
What is the ATOTN?
Air Traffic Operational Telephone network
What is SELCAL?
Selective calling
Basically a way of reducing pilot fatigue by no longer requiring them to maintain a constant listening watch. A selective call will be sent to the aircraft which will create a visual and aural alarm in the cockpit letting them know that ATC wishes to talk to them.
What is ACARS?
Aircraft Communications Addressing and Reporting System
A system similar to CPDLC which is used by the airline/operater to speak or download parameters from the aircraft.
What three types of ACARs messages are there?
- Air Traffic Control ATC
- Aeronautical Operational Control AOC
- Airline Adminstrative Control AAC
What is the AFTN?
Aeronautical Fixed Telecommunications Network
What is MOTNE?
Meteorological Operation Telecommunication Network Europe.
What is the range equation?
D=C (speed of light) x Time
2
Plugging the speed of light into a simple speed, distance, time equation but by dividing by two as you only want to know the distance to not to and from.
What is the speed of light?
3x108m/sec
300,000,000m/sec
Who issues codes?
Authorised Authority.
What does ADS-B broadcast for the aircraft’s position?
- Horizontal
- Vertical
- Velocity
What are the AFTN message priorities?
- SS
- DD & FF
- GG & KK
What sort of messages come under the SS priority?
Distress messages and traffic
What sort of messages come under DD priority?
Urgency messages and traffic
What are the sort of messages that come under GG priority?
Met Messages
Flight regularity messages
Aeronautical Adminstrative messages
NOTAMS
What sort of messages come under FF priority?
- FPL- incl FPL messages such as DLA, CHG, CNL, ARR, DEP
- Co-ordination messages- CPL (current FPL), EST (estimate), CDN (coordination), ACP (acceptance), ACK (acknowledgement)
- Supp messages- RQP (request FPL), RQS (request supp FPL info), SPL (supplementary FPL)
- Control messages
- Traffic information
- Met info
- Air traffic
What sort of messages come under KK priority?
Reservation messages
General a/c operating agency messages
What is OFTS?
Overseas Fixed telecommunications Service
What factors determine RADAR coverage?
- Aerial size, shape and height
- Size of the target
- Atmospheric conditions
- Transmitter power
- Receiver Efficiency
- PRF
- Pulse length
What do ATC require when employing a RADAR aerial?
Narrow Beam in azimuth
Wide beam in elevation
Does Mode S provide better resolution over an SSR installation?
Yes
Has mode S brought benefits by improving pilots position reports?
No
What is Slant Range?
The line of sight distance along a slant direction between two points which are not at the same level relative to a specific datum.
Why do ATC use VHF frequencies?
This is because the sounds do not require excellent audio clarity of tone unlike radio broadcasts of music.
What does 1090 ES mean
ADS B extended Squitter which transmits the aircraft information on 1090MHz
