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Nav Aids Flashcards

1
Q

What is the Air Range?

A

Air Range is 108 - 137 MHz

Nav Aids are 108 - 118 MHz

VHF comms are 118 - 137MHz

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2
Q

What is the principle of operation for the VDF?

A

Receiving station receives VHF signal from aircraft and using an adcock antenna on the ground is able to determine the aircrafts heading using phase difference.

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3
Q

What frequency range does a VDF operate in?

A

118-137 MHz LOS & VHF Comms range

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4
Q

What is the accuracy of the VDF?

A 
class A: accurate to a range within ± 2°;
class B: accurate to a range within ± 5°;
class C: accurate to a range within ± 10°;
class D: accurate to less than class C, 10°+
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5
Q

Where is the Variation applied in the case of a VDF?

A

At the station

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6
Q

What are the errors of the VDF?

A
  1. Super-refraction
  2. Sub-refraction
  3. Sporadic-E
  4. Ground reflected waves (Propogation Error) - destructive waves
  5. Multipath (Siting Error)
  6. Intervening High Ground / Multipath
  7. Synchronous Transmissions
  8. Overhead Error
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7
Q

What is the principle of operation for the NDB?

A

The NDB is a ground based radio station which broadcasts an onmidirectional signal in the LF and MF bands.

A Loop and sense arial in the aircraft constantly rotates to find the null point and determines a relative bearing of the NDB from the aircraft

A sense arial is added to the loop arial to create a cartoid and remove the ambiguity.

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8
Q

What equipment is required to direction find using an NDB?

A
  1. An NDB (on the ground)
  2. Loop and sense antenna on the a/c
  3. Automatic Direction Finder (ADF) reciever on the a/c
  4. Cockpit display instrument (RBI, RMI)
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9
Q

What frequency range does a NDB operate in?

A

190 - 1750 kHz

(normally operate at 200 - 455 kHz)

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10
Q

What is the emmission class for the NDB?

A

N0N A1A - (BFO On and No DF’ing while on)

N0N A2A

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11
Q

What are the two types of NDB’s?

A

A short range NDB (Locator) - 10-25nm - 2 letter ident

A long range NDB (En-Route) - 50nm+ - 3 letter Ident

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12
Q

What is the accuracy of the NDB?

A

±5° but no failure flags so you have to listen to the ident all the way down

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13
Q

Where is the variation applied in the case of the NDB?

A

At the aircraft

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14
Q

What are the errors for the NDB?

A
  1. Static (Thunderstorms/Precipitation)
  2. Night effect (change of ionosphere)
  3. Station Interference
  4. Coastal Refraction
  5. Multipath
  6. Quadratial
  7. Dip Error
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15
Q

How large is the cone of confusion for a NDB?

A

40°

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16
Q

What is Promulgated Range (DOC)?

A

The promulgated range is the maximum range in which you can receive a transmission from an NDB and be guaranteed that you wont be affected by an adjacent NDB.

ONLY VALID DURING THE DAY!!

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17
Q

What’s the difference between homing and tracking?

A

Homing is heading straight to the beacon as per the needle. In strong wind conditions, it could result in spiraling/ approaching from behind - Carve of pursuit.

Tracking is moving to the beacon whilst correcting for wind.

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18
Q

What is the principle of operation for the VOR?

A

The VOR ground station tramits two independent signals, the Reference Signal and the Variable Signal

The reference phase is FM, omnidirectional and rotates CW at 30Hz (1800rpm)

The veriphase is AM at 30Hz which is in phase with ref at 360° Mag

MAG BEARING BY PHASE COMPARISON

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19
Q

What frequency range does the VOR operate in?

A

VOR is 108 - 117.95 MHz

ILS Localiser is 108.1 - 111.95

Evens after decimal = VOR

Odds after decimal = ILS Loc

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20
Q

What is the emmission class for a VOR?

A

A9W

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21
Q

What is the accuracy of the VOR?

A

VOR Total Error - ±5°

Ground Station - ±1°

Airbourne Equipment - ±3°

Random Error - ±1°

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22
Q

What are the different types of VOR in use?

A

Conventional VOR (CVOR): a first- generation VOR station emitting signals by means of a rotating antenna;

Doppler VOR (DVOR): a second- generation VOR station emitting signals by means of a combination of fixed antennas utilising the Doppler principle;

Broadcast VOR (BVOR); used for ATIS broadcast

en route VOR for use by IFR traffic;

Terminal VOR (TVOR): a station with a shorter range used as part of the approach and departure structure at
major airports;

Test VOR (VOT): a VOR station emitting a
signal to test VOR indicators in an aircraft.

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23
Q

What equipment is required to use the VOR?

A

VOR on the ground

The antenna on the aircraft

The receiver on the aircraft

The indicator in the aircraft

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24
Q

What is full scale deflection on the VOR?

A

±10°

2° per dot on a 5 dot instrument

5° per dot on a 2 dot instrument

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25
Q

How large is the cone of ambiguity for a VOR?

A

50°

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26
Q

What are the errors for a VOR?

A
  1. Siting Error (CVOR only)
  2. Propagation error (scalloping) - Ground reflections distort or degrade the signal worst at low range. Scalloping (Fast oscilation), Beam Bend (Slow)
  3. Station Interference - Cure is Designated Operational Coverage (Valid Day or Night)
  4. Super- Refraction
  5. Sub- Refraction
  6. Sporadic-E
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27
Q

In the case of a VOR, under what conditions will the monitoring system transfer from master to standby?

A
  1. Change in measured radial of 1° at monitor station
  2. A reduction in the carrier wave signal by more than 15%
  3. A reduction in either, or both of the reference and directional signal by more than 15%
  4. Failure of the monitor

IDENT will be off

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28
Q

Where is variation applied in the case of a VOR?

A

At the VOR, on the ground

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29
Q

How many letters in the VOR ident?

A

3 letters broadcast of a frequency of 1020 MHz

No ident indicates an unreliable or offline system

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30
Q

What frequency range does the DME operate in?

A

UHF band 960-1215MHz

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31
Q

In the case of the DME, what is the difference in frequency between the interrrogation and reply signals and why do they differ?

A

They differ by 63MHz which is to stop the interrogator looking for it’s own reflections.

In the case of X beacons, aircraft transmit from 1025 - 1087 MHz - The ground replies 63MHz LOWER

In the case of Y beacons, aircraft transmit from 1088 - 1150 MHz - The ground replies 63MHz HIGHER

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32
Q

What equipment is required to use the DME?

A

The ground component is the DME transponder

The airbourne component is the DME interrogator

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33
Q

What is the emmission class for the DME?

A

P0N

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34
Q

What is the principle of operation for the DME?

A

Principle of operation is slant range by pulse timing, effectivly a form of secondary surveilance radar using pulse pairs.

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35
Q

What are the two catagories of DME?

A

DME/N (Normal spectrum or standard DME) common at most facilities

DME/P (Prescision DME used in MLS)

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36
Q

What is a Terminal DME (TDME)?

A

It’s a DME, colocated with another navigational aid which has been corrected to provide a 0nm range at touchdown of an instrument approach

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37
Q

How do you tune and identify the DME?

A

It’s paired with the colocated VOR or ILS frequency so you may only ever have to tune it if flying in an ill equipped GA aircraft.

The ident is a 3 letter code transmitted at 1350Hz every 40s

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38
Q

In the case of the DME, what is the response delay in both X and Y Beacons and what is it’s purpose?

A

Low Band - X Beacon: 50 µs

High Band - Y Beacon: 74 µs

It’s purpose is to prevent multipath.

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39
Q

What is the Radar Mile equation in the case of DME?

A

The radar mile is: Range = (Time in µs - TAT) / 12.36

40
Q

What are Pulse Pairs in the case of the DME?

A

Each interrogation and reply signal comprises a series of pulse pairs. The length and pulse code (time interval )of each pair if fixed. (Think Sonardyne Wideband)

For DME/N:

X-Channels - Interrogate and reply at 12µs

Y-Channels - Interrogate at 36µs and reply at 30µs

41
Q

How does the DME transponder differentiate between different aircraft?

A

The pulse repitition frequency (PRF) is randomly jittered.

42
Q

What is an Echo-Protection circuit used in conjunction with a DME?

A

It is used to ensure that only pulse pairs with the same jittered frequncy are used, all others are discarded.

43
Q

What happens in Stanby Mode when interrogating a DME?

A

Once the DME frequency is selected, the interrogator enters standby mode until a sufficient number of ‘squitter’ pulses have been recieved before entering search mode.

44
Q

What happens once Search Mode is entered when interrogating a DME?

A

In search mode the interrogator increases the average PRF to 150 ppps to increase the search time.

If distance indications arent acquired after 15,000 pulse pairs have been transmitted, it drops to 60 ppps. If no range is aquired after a further 30 seconds it further reduces to 30ppps.

If the signal is lost for 10 seconds it goes into a Memory Mode before going into search mode again.

45
Q

What data does the DME calculate in Tracking Mode?

A

In Tracking Mode it calculates the distace in NM and the groundspeed in kts

46
Q

At what point does the DME beacon become saturated?

A

It is limited by a total of 2700 ppps.

Assuming 95% of a/c tracking and 5% searching it will become saturated at approximately 100 a/c.

At this point it reduces the gain to prioritise the closest a/c

47
Q

What has to be condered with DME range?

A

DME range is a slant range and differs from the ground range the closer and higher the a/c is to the DME. Pythagoras will be required to correct.

48
Q

What has to be considered with DME groundspeed calcs?

A

The DME is actually calculating a rate of change of slant range not ground range. The speed calc will get less accurate as you get closer.

GS is less than actual

Range overreads, Speed underreads

49
Q

What is the accuracy of the DME?

A

DME/N ±0.25nm + 1.25% of Range

DME/P (After 1/1/89) 0.2nm

50
Q

What are the errors of the DME?

A
  1. Airbourne Equipment Error
  2. Ground Equipment Error
  3. Propagation Error
51
Q

What are the 3 components of the ILS?

A
  1. The Localiser - Lateral guidance
  2. The Glide Path
  3. The DME
52
Q

What are the operating frequencies of the ILS?

A

Localiser - 40 frequencies from 108 - 112MHz (Odds) VHF

Glideslope - 333MHz UHF

Frequency Paired!!

53
Q

Where are the components of the ILS located in relation to the runway?

A

The localiser antenna is located on the extension of the runway centreline at the stop end.

The glide-path antenna should be located 300 metres beyond the runway threshold, laterally displaced approximately 120 metres to the side of the runway centre line.

54
Q

What is the frequency, modulation and identification assigned to the ILS marker beacons?

A

The modulation frequencies are:
— outer marker: 400 Hz; (Blue); 3.5 - 6 nmls
— middle marker: 1 300 Hz; (Amber) ; 0.5 nmls
— inner marker: 3 000 Hz. (White); <0.5 nmls

The audio frequency modulation
— outer marker: 2 dashes per second continuously;
— middle marker: a continuous series of alternate dots and dashes;
— inner marker: 6 dots per second continuously.

55
Q

What is the full scale deflection of the ILS?

A

Localiser - 2.5° displacement from the ILS centre line;

Glideslope - 0.7° from the ILS GP centre line.

56
Q

What is the coverage and range of the ILS?

A

Localiser coverage area is 10° on either side of the centre line to a distance of 25 NM from the runway, and 35° on either side of the centre line to a distance of 17 NM from the runway;

Glideslope coverage area is 8° on either side of the centre line to a distance of minimum 10 NM from the runway.

57
Q

How do you calculate Rate of Descent?

A
  1. RoD = 5 x Groundspeed (ONLY FOR 3° GS)

otherwise

RoD = 5 x Groundspeed (n/3) n=GS Angle

  1. RoD = % Gradent x Groundspeed
58
Q

What are the ILS Operation Catagories?

A

Facility Performance Category 1: Provides ILS guidance down to 200ft or less

Facility Performance Category 2: Provides ILS guidance down to 100ft or less

Facility Performance Category 3: With the aid of ancillary equipment where necessary, can provide ILS guidance down to and along the surface of the runway.

59
Q

How accurately does an ILS have to be flown in order to be considered as established?

A

Within the half-full scale deflection of the required track;

The aircraft has to be established within the half-scale deflection of the LLZ before starting descent on the GP;

Maximum of half-scale fly-up deflection of the GP in order to stay in protected airspace.

IF NOT, GO AROUND!

60
Q

What is the emmission class of the ILS?

A

A8W

61
Q

What are the errors of the ILS?

A
  1. Limited to 40 channels
  2. Beam bending
  3. Scalloping
  4. Beam noise
  5. Commercial FM interference
  6. Subtle failure flags
62
Q

What is the vertical coverage of the Glideslope?

A

Lower Limit - 0.45 x ø

Upper Limit - 1.75 x ø

63
Q

What is the ILS mode of operation for determining position laterally from the runway centreline?

A

The ILS Localiser emits two AM lobes in the VHF band, one each side of the centreline.

The yellow lobe is emitted left of the centreline at 90 Hz

The blue lobe is emitted right of the centreline at 150 Hz

The amount of modulation increases linearly toward the outer aspect and the receiver uses this to determine a Difference in Depth of Modulation (DDM) and display a corresponding corrective action.

64
Q

What is the ILS mode of operation for determining position vertically from the runway centreline?

A

The ILS Localiser emits two AM lobes in the UHF band, one each side of the glideslope.

The yellow lobe is emitted above the glideslope at 90 Hz

The blue lobe is emitted below the glideslope at 150 Hz

The amount of modulation increases linearly toward the outer aspect and the receiver uses this to determine a Difference in Depth of Modulation (DDM) and display a corresponding corrective action.

65
Q

In what circumstances will warning flags appear for the ILS?

A

The absence of the carrier frequency

Absence of the 90 and 150-Hz modulation simultaneously

The percentage modulation of either the
90 or 150-Hz signal is reduced to 0.

66
Q

What is the ILS critical area?

A

An area of defined dimensions around the localiser and glideslope antennas where vehicles, including aircraft, are excluded during all ILS operations.

67
Q

What is the ILS sensitive area?

A

An area extending beyond the critical area where the parking and/or movement of vehicles, including aircraft, is controlled to prevent the possibility of unacceptable interference to the ILS signal during ILS operations.

68
Q

Where is the first false glideslope found and what is the action to prevent incorrect capture?

A

Found at twice the normal glideslope, 6° on a 3° glideslope

Always intercept from below.

69
Q

What is the principle of operation for the MLS?

A

MLS also known as a Time Reference Scanning Beam (TRSB), uses Time Division Multiplexing (TDM) to transmit a packet of info on a single channel

70
Q

How is Azimuth and Elevation determined for MLS?

A

The Time Referenced Scanning Beam (TRSB) scans a horizontal and vertical sector conducting a TO and From sweep in 9000 micro seconds and repeated 13 times a second.

The elevation scan is repeated 39 times a second.

71
Q

What is the operating frequency of the MLS?

A

5031 - 5090.7 MHz

SHF Band

200 Channels (rather than 40 for ILS)

72
Q

What is the emmission classification for the MLS?

A

N0X G1D

73
Q

What is the area of coverage for the MLS?

A

A sector of ± 40° of the centre line out to a range of 20 NM from the threshold

74
Q

What is the error for the MLS?

A

95 % lateral and vertical accuracy within 20 NM (37 km) of the MLS approach reference datum and 60 ft above the MLS datum point

75
Q

What is relationship between the MTR and the Pulse Repetition Frequency (PRF)?

A

The greater the range required, the lower the PRF (No of pulses per second)

The rotation speed of the dish also has to be slower

76
Q

What is the formlula for the Max Theoretical Unambiguous Range?

A

Range in KM = C / PRF x 2

The quick method is to divide 81000 by the PRF

77
Q

What defines the MTR of a radar?

A

Minimum Pulse length

78
Q

Why is a Moving Target Indicator used in radar?

A

An MTI removes contacts from static objects such as ground features by jittering the PRF and calculating the dopper shift to only display moving targets.

Aircraft moveing tangentially will also be removed

79
Q

How does Atmospheric Attenuation affect radar?

A

Water droplets and vapour in the atmosphere have the effect of attenuating the signal by coverting energy to heat.

Long range radar and higher frequencies are most affected.

80
Q

How does Sub and Super Refraction affect radar?

A

Sub refraction is often caused by warm, moist air moving over a cooler surface and causes the beam to bend upwards, reducing the max radar range.

Super refraction causes the beam to bend downward toward the earth causing increased range but also ambiguous and cluttered returns.

81
Q

What are the two main functions of the Airbourne Weather Radar?

A

Weather avoidance and navigation by use of Map mode

82
Q

What is the typical frequency and wavelength of the AWR?

A

Wavelength is approx 3cm and frequency is approx 9 GHz (SHF)

83
Q

How is the Slotted Planar Array used in AWR stabilised?

A

It’s stabilised in the horizontal axis (Roll) but can be adjusted in pitch as required, or slaved if auto selected

84
Q

What are the two radiation patterns used in AWR?

A

Cosec2 used in the Mapping Mode (older systems) and a Pencil beam (Cone) used in the Wx function (or both if newer system)

85
Q

What is the typical beam width of the pencil beam?

A

3 - 5°

86
Q

What do the colours represent on the AWR display?

A
87
Q

What direction should the AWR be tilted when climbing?

A

The AWR should be tilted downwards

88
Q

How can turbulence and windshear be detected using modern weather radar?

A

AWR uses doppler shift to determine the relative velocity of particles ahead of the aircraft

89
Q

What is the principle of operation for SSR?

A

Slant range by pulse timing.

Similar to the DME only the ground station is the interrogator and the aircraft is the responder.

90
Q

What is the interrogation and reply frequency of SSR?

A

Ground - Tx is 1030 MHz and Rx is 1090 MHz

Aircraft - Tx is 1090 MHz and Rx is 1030 MHz

Think higher frequency in the air!

91
Q

What is the purpose of the P2 transmission in the case of Mode A+C SSR?

A

Each interrogation from the ground station comprises 3 pulses: P1, P2 and P3. P2, the control pulse is transmitted 2µs after P1. P3 is transmitted 8 µs after P1,

P1 and P3 pulses are transmitted by the rotating radar head within a directional beam, 2° - 3° wide. The control pulse, P2, is transmitted from an omnidirectional aerial,

If the amplitudes of P1 and P3 are greater than P2, as in the figure below, then it is a valid main lobe interrogation.

92
Q

What are the reported altitude step increments in the case of Mode-C and Mode-S SSR Transmissions?

A

Mode-C - 100ft (Valid to 50ft)

Mode S - 25ft (Valid to 12.5ft)

93
Q

How many individual transponder (Squawk) codes exist in the case of Mode A, C and S?

A

Mode A & C - 12 bit, 4 digits so 4096 individual codes

Mode S - 24 bit hex codes so 16 777 214 codes, each airfrace assigned its unique code!

94
Q

What data sets are transmitted as part of Mode S Elementary Surveillance (ELS)?

A

Automatic reporting of Aircraft Identity. This is the callsign used in flight and is automatically presented to the controller.

Transponder Capability Report. A technical function to enable ground systems to identify the data link capability of the transponder.

Altitude reporting in 25 ft intervals. (subject to aircraft capability).

Flight status. A technical function showing if the aircraft is airborne or on the ground.

SI code capability. A technical function to identify transponders capable of operating within a Surveillance Identifier (SI) code ground environment. Basic functionality with SI code capability is the minimum level permitted for operations in European airspace.

Data-Link: Mode S interrogators and transponders communicate with each other using a data-link system. To detect other Mode S transponders, an all-call message is broadcast at intervals. Normal SSR transponders respond to this in Mode A or C. Mode S transponders recognise the all-call interrogation as a roll-call request and transmit a response that includes the aircraft’s identity/address. This 56-bit message is transmitted on one of 4 communication protocols:”

Notes From: Slate-Ed Ltd. “EASA ATPL Radio Navigation.” Slate-Ed Ltd, 2013. iBooks.

Check out this book on the iBooks Store: https://itunes.apple.com/gb/book/easa-atpl-radio-navigation/id590362787?mt=11

95
Q

Which aircraft have to be Mode S Enhanced Surveillance equipped?

A

All fixed wing aircraft, having a maximum take-off mass greater than 5700 kg or a maximum cruising true airspeed in excess of 250 kt, intending to fly IFR as General Air Traffic (GAT), must be Mode S EHS compliant.

96
Q

What data sets are transmitted as part of Mode S Enhanced Surveillance (EHS)?

A

As per ELS plus the following nine down-linked aircraft parameters (DAPs):

  • Magnetic Heading
  • Indicated Airspeed
  • Mach Number
  • Vertical rate
  • Roll angle
  • Track Angle Rate
  • True Track Angle
  • Groundspeed
  • Selected Altitude

RNAV (2 decks)

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