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Module 13 EASA Part 5 Radar > Chapter 3 - Air Traffic Control (ATC) > Flashcards

Chapter 3 - Air Traffic Control (ATC) Flashcards

1
Q

What are the frequencies associated with the transponder?

A

Ground station - transmit on 1030 MHz and receive on 1090 MHz

Airborne station - transmit on 1090 MHz and receive on 1030 MHz

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2
Q

Why do transponders and ATC transmit and receive on different frequencies?

A

So their transmitters don’t swamp their receivers

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3
Q

What is the width of each interrogation pulse?

A

0.8μs

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4
Q

What is the P1 and P3 pulse spacing for each of the modes?

A

Mode A - 8μs
Mode B - 17μs
Mode C - 21μs
Mode D - 25μs

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5
Q

What is the purpose of Mode A?

A

Provide functional identification, distinct from individual identification

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6
Q

What is the purpose of Mode C?

A

Provide digitised barometric altimeter reading in increments of 100 ft

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7
Q

What is mode interlacing?

A

The interrogator operating on different modes in turn

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8
Q

What are the two modes which are deemed the most important, and are therefore always included in a three mode interlacing method?

A

A and C

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9
Q

What is the pulse width of replies from the aircraft transponder?

A

0.45μs

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10
Q

Describe a transponder reply?

A
  • F1 and F2 framing pulses spaced 20.3μs apart
  • Aircraft reply to the particular mode between framing pulses
  • Additional pulse, called an SPI or special position ident, if requested after second framing pulse
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11
Q

What happens when ATC ask the pilot to squawk ident?

A

The pilot presses IDENT on the control unit which adds a special pulse 4.35μs after F2 on a mode A reply for 20 seconds

Causes aircraft echo to flash or otherwise be highlighted on ATC display

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12
Q

What is the code 7700 used for on transponders?

A

Used to signify an aircraft emergency

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13
Q

What is the code 7600 used for on transponders?

A

Used to indicate radio failure

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14
Q

What is the pulse spacing between P1 and P2?

A

2μs

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15
Q

What is P2 also known as?

A

Control pulse

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16
Q

What is the pattern of the transmitted P2 pulse?

A

Omnidirectional

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17
Q

How does the decoder process the ATC interrogation?

A

Video output from the detector is fed to the delay line and coincidence gate concurrently

Four connections are critically spaced along the delay line

Connections from the delay line are taken to the coincidence gate via the controller Mode switches in the cases of Mode A, B and D

If the pulses arrive at the coincidence gate at the right time, it will give out a single pulse to the encoder

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18
Q

Which mode is permanently connected?

A

Mode C

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19
Q

Why are suppression pulses fed out from the transponder?

A

Prevent interference between L-band equipment (DME and transponder)

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20
Q

What is the duration of the suppression pulse?

A

30μs

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21
Q

What is ‘fruit’ in terms of transponders?

A

Unwanted replies to interrogations appearing on an ATC display

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22
Q

What are some of the common causes of ‘fruit’?

A
  • Replies from an interrogated aircraft received by other ground receivers
  • Aircraft replies to side lobe interrogations
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23
Q

What are some of the common techniques for ‘de-fruiting’?

A
  • Side lobe suppressions
  • Different PRF from adjacent ground stations
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24
Q

Describe group count down?

A

The aircraft transponder has a certain duty cycle to prevent overloading

It is a variable quantity, dependant on number of interrogations, mode and code used for the reply

If the allowable duty cycle is likely to be exceeded, internal circuitry in the transponder de-sensitizes the receiver

Receiver will reply to the nearest interrogator and not the distant ones

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25
Q

Why can AGC not be used in a transponder?

A

Because SLS circuits would not work

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26
Q

How much of a difference must there be between P1 and P2 for the SLS to accept wanted interrogations?

A

At least 9dB difference, not only at the aerial but also into the SLS comparator

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27
Q

Describe the local oscillator in the transponder?

A

Crystal controlled and working at a frequency in the VHF band

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28
Q

What are the higher levels of automation available to Mode S equipped transponders?

A
  • Bi-directional air-to-ground data downlink
  • Extended length messages (ELM)
  • Multisite message protocol
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29
Q

What is Mode S Lockout?

A

After interrogation by ‘all call’ interrogation and reply, the address and location of the Mode S aircraft is entered into a roll-call file

On the next scan, the Mode S aircraft is discreetly addressed

Discrete interrogation will desensitize the Mode S transponder to late Mode S all call interrogations

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30
Q

How might adjacent Mode S interrogators transmit information about aircraft flying between their airspace and what does this mean for the travelling aircraft

A

By land line

The need to remove the Mode S Lockout is removed, and the transponder can continue to receive discreet interrogations

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31
Q

What is the type of code transmitted in the Mode S interrogation?

A

Differential Phase-Shift Keying (DPSK)

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32
Q

What is the modulation of the downlink transmission from the transponder?

A

Pulse Position Modulation (PPM)

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33
Q

What is a Diversity System?

A

A Mode S transponder which is equipped with two antennas, as a means to improve air to air surveillance and communications

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34
Q

In a diversity Mode S transponder, how is the choice of antenna handled?

A

Whichever antenna has the strongest strength of detected signal will be used

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35
Q

How many transponders can be active at once?

A

Only one, the other is in standby mode

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36
Q

How is the identity code and control information provided to the selected transponder?

A

By ARINC 429 control word

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37
Q

What is the purpose of the non-volatile flight memory in the ATC transponder?

A

For sixty three flight legs

38
Q

What does the presence of a P4 pulse mean in an interrogation?

A

ATCRBS replies from a Mode S transponder are terminated

39
Q

What is the result if the P4 pulse duration is 1.6μs?

A

A Mode S reply is generated 128 μs after the leading edge of the P4 pulse

40
Q

What is the purpose of the P1 P2 pulsed pair?

A

Suppress replies from ATCRBS transponders to avoid synchronous garble

41
Q

What does the P6 pulse contain in the Mode S interrogation DPSK signal?

A

Interrogation data in the form of DPSK modulation

42
Q

Describe P6 in DPSK interrogation?

A

Contains a series of chips which are 0.25 μs in duration and are unmodulated

The chips start 0.5 μs after Synch Phase Reversal (SPR)

If a chip is a phase reversal, it is a logic 1

There are either 56 or 112 bits in P6

43
Q

How is SLS achieved on Mode S only all call interrogations?

A

Overlaying pulse P5 on P6 to prevent the transponder detecting the SPR position on the P6 pulse

44
Q

What does the Mode S reply consist of?

A

Preamble and data block

45
Q

How is the data block formed?

A

By Pulse Position Modulation (PPM) encoding of the reply data

46
Q

When will the first preamble of a reply occur?

A

128 μs after the SPR of the received P6 pulse of a Mode S interrogation

or

128 μs after the P4 pulse of an ATCRBS/Mode S all call interrogation

47
Q

How does the Mode S transponder operate for TCAS?

A

Communications link between TCAS equipped aircraft, to coordinate avoidance procedures

48
Q

How does the Mode S transponder communicate with its own TCAS system?

A

TCAS co-ordination high speed ARINC 429

49
Q

What is a caution area?

A

An area of airspace which begins 35-40 seconds from the time an intruder aircraft is predicted to enter the TCAS aircraft’s collision area

50
Q

How does the TCAS collision area vary?

A

Varies in size contingent upon closure rate

51
Q

Describe ‘other traffic’?

A
  • Not classified as intruder or proximate traffic
  • Within ±2700 feet vertically
  • Within the range of the display
  • Inhibited during TAs and RAs
52
Q

Describe ‘proximate traffic’?

A
  • Within 6 nm radius
  • ± 1200 feet vertically
  • Displayed in conjunction with a TA or RA
53
Q

When is a RA designed to occur?

A

Intruder’s predicted flight path is within 20 to 30 seconds from entering the TCAS aircraft’s collision area

54
Q

What is the difference between corrective advisory and preventative advisory?

A

Corrective instructs the pilot to deviate from the current vertical rate, while preventative instructs the pilot to avoid certain deviations from current vertical rate

55
Q

What is the priority of environmental alerts in transponder aircraft?

A
  1. Stall
  2. Windshear
  3. GPWS
  4. TCAS
56
Q

When will TCAS revert to Traffic Alert Only Mode?

A

When it is inhibited by stall, windshear or GPWS

57
Q

What will be displayed about an intruder aircraft at a TA?

A
  • Range
  • Bearing
  • Altitude of the intruder aircraft relative to the TCAS aircraft
58
Q

What will TCAS announce once the intruder’s flight path no long coincides with the Mode S transponder aircraft?

A

Clear of conflict

59
Q

What is the drawback of TCAS, with regards to which aircraft will generate a TA?

A

Only works with intruder aircraft whose transponders reply in Mode A

60
Q

To what type of aircraft are RAs limited to?

A

Aircraft responding with Mode C or Mode S replies with altitude data

61
Q

How do Mode S transponders announce their presence?

A

Transmitting a squitter message once each second

62
Q

Why must Mode S transponders actively search for Mode C equipped aircraft?

A

Mode C transponders don’t transmit squitter

63
Q

What happens when the Mode S transponder detects a Mode S or Mode C intruder?

A

TCAS places the intruder in TRACK

64
Q

How many intruders can TCAS track?

A

Up to 30

65
Q

What is TAU?

A

Maximum time the flight crew need to discern a collision threat and take evasive action

66
Q

What is the calculation for TAU?

A

Speed and path of host aircraft (in nm)
/
Closure rate of intruder aircraft (in knots)

67
Q

In collision avoidance, time-to-go closest point of approach (CPA) is much more important than distance-to-go CPA?

A

Pilots will always have the same amount of time to react regardless of closing speed

68
Q

Under what conditions could an intruder slip in dangerously close without violating the TAU boundaries?

A

Rate of closure is very low, such as in an overtaking situation

69
Q

What provides added protection against slow closure rates?

A

Distance modification called DMOD

70
Q

What is the TCAS airspace density TCAS can handle?

A

Aircraft densities of 0.3 transponder equipped aircraft per square nautical mile

71
Q

At what height will TCAS check for targets on the ground?

A

1700 feet

72
Q

At what perceived height above ground level, will TCAS consider a target to be on the ground?

A

180 feet

73
Q

How does TCAS calculate the height of a target aircraft?

A

Takes the difference between its own barometric altitude and radio altitude to determine the approximate elevation of the ground above sea level

Subtracts the latter from the barometric altitude given by the target aircraft, to calculate it’s approximate altitude above sea level

74
Q

What kind of threat and TCAS alert is represented by the colour RED?

A

Immediate threat and RA

75
Q

What kind of threat and TCAS alert is represented by the colour AMBER?

A

Moderate threat and TA

76
Q

What would CYAN represent in TCAS?

A

Proximate traffic and other traffic

77
Q

What is the TCAS symbol for TA?

A

Solid amber circle

78
Q

What is the TCAS symbol for RA?

A

Solid red square

79
Q

What is the TCAS symbol for proximate traffic?

A

Solid cyan diamond

80
Q

What is the TCAS symbol for other traffic?

A

Hollow cyan diamond

81
Q

What is the altitude tracking volume?

A

TCAS transponder equipped aircraft that are within a relative altitude range of ± 9900 feet

82
Q

What is the surveillance update period?

A

TCAS transmits interrogations separately to ATCRBS equipped aircraft and Mode S equipped aircraft once every second and listens for responses for the remainder of the second

83
Q

How is ensured that the surveillance update period isn’t synchronised with ground based transmitters or other Mode S equipped aircraft squitter emissions?

A

By randomly jittering the period, so that it occurs every 0.95 to 1.05 seconds

84
Q

What is the format of squitter transmissions from Mode S equipped aircraft?

A

Downlink format eleven (DF-11)

85
Q

How do Mode-S transponders indicate their presence?

A

By transmitting a squitter message once every second

86
Q

What is the list of tracked aircraft TCAS uses?

A

Roll Call

87
Q

What is synchronous garble?

A

When two or more aircraft under Mode C surveillance have ranges from the TCAS aircraft which are close together, their received replies overlap in time

88
Q

What are the techniques used to reduce synchronous garble?

A
  • Use of the mode C only all-call interrogations
  • Use directional emissions
  • Whisper shout techniques
89
Q

What is whisper shout?

A

Dividing the airspace around an aircraft into range segments by varying the transmission power

90
Q

What does the ABOVE/NORMAL/BELOW switch do for TCAS?

A

Above - threats +7000 ft to -2700 ft
Normal - threats ±2700 ft
Below - threats +2700 ft to -7000 ft

91
Q

How will targets with no altitude reporting be displayed by TCAS?

A

It will assume they are at co-altitude

92
Q

When will an OFF SCALE flag appear on EHSI with regards to TCAS?

A

The selected range does not allow a threat to be plotted

Module 13 EASA Part 5 Radar (4 decks)

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