ADF - Dgca question bank for pilots

Results

#1. The phenomenon of coastal refraction which affects the accuracy of ADF bearings:

is most marked at night.

can be minimised by using beacons situated well inland.

can be minimised by taking bearings where the signal crosses the coastline at right angles.

is most marked one hour before to one hour after sunrise and sunset.

Coastal Refraction. Radio waves speed up over water due to the reduced absorption of energy (attenuation) compared to that which occurs over land. This speeding up causes the wave front to bend (Refract) away from its normal path and pull it towards the coast. Refraction is negligible at 90 to the coast but increases as the angle of incidence increases.

For an aircraft flying over the sea the error puts the aircraft position closer to the coast than its actual position.

The effect can be minimised by:

Using NDBs on or near to the coast.

Flying higher.

Using signals that cross the coast at or near to 90

#2. An aircraft is intending to track from NDB ‘ A’ to NDB ‘B’ on a track of 050° (T), heading 060° (T). If the RBI shows the relative bearing of ‘ A’ to be 180° and the relative bearing of ‘B’ to be 330° then the aircraft is:

Port of track and nearer ‘ A'.

Port of track and nearer ‘B'.

Starboard of track and nearer ‘ A'

Starboard of track and nearer ‘B'.

the plane’s heading is known, but the plane’s actual track is not. Also the bearing from A to B is known– it is the intended track.

Bearing from point A to plane = reciprocal of 60 180 = reciprocal of 240 = 60.

Bearing from point B to plane = reciprocal of 60 330 = reciprocal of 390 = reciprocal of 030 = 210

Draw a sketch of A and B, with B 50 degrees from A. Draw the bearings from A and B to the plane– the plane is located where these bearing lines cross–

and it will be clear that the plane is right of the intended track, and closer to B than A.

#3. ADF Quadrantal Error is caused by:

static build up on the airframe and St. Elmo's Fire.

the aircraft's major electrical axis, the fuselage, reflecting and re-radiating the incoming NDB transmissions.

station interference and/or night effect.

NDB signals speeding up and bending as they cross from a land to water propagation path

Quadrantal Error

The wave front from the NDB can be distorted by the aircraft’s structure as it approaches the aerial.

This effect is compounded by an emf induced in the receiver aerial by the signal re-radiating from metallic surfaces.

The aircraft structure bends the signal path.

The error is called “quadrantal error” because the effect is worst for signals arriving from 45° and 135° left and right of the nose, the four “quadrants”.

Quadrantal error is small and predictable.

It can be compensated during the installation of the receiver aerial and any residual errors can be shown on a quadrantal error card kept near the instrument.

Modern receivers completely remove it.

#4. The overall accuracy of ADF bearings by day within the Promulgated Range (DOC) is:

± 3°

± 5°

± 6°

± 10°

The accuracy of ADF is /-5° within the designated operational coverage, by day only. This refers to the measured bearing and does not include any compass error.

#5. In order to Tune, Identify and Monitor NON A1A NDB emissions the BFO should be used as follows:

Tune on Identify on Monitor off

Tune on Identify on Monitor On

Tune on Identify off Monitor off

The NDBs have a 2 or 3 letter identification and there are two types of emission:

N0NA1A

N0NA2A

To make the unmodulated parts of the A1A signal audible, ADF incorporates a BFO.
Selecting the BFO on makes the N0N carrier wave audible and allows the A1A type of ident to be heard.
BFO is not needed for an A2A signal which is already modulated to an audible frequency
Hence when using N0NA1A beacons, the BFO should be selected ON for (manual) tuning, identification and monitoring.

#6. The magnitude of the error in position lines derived from ADF bearings that are affected by coastal refraction may be reduced by:

selecting beacons situated well inland

only using beacons within the designated operational coverage.

choosing NON A2A beacons.

choosing beacons on or near the coast.

For an aircraft flying over the sea the error puts the aircraft position closer to the coast than its actual position.

The effect can be minimised by:

Using NDBs on or near to the coast.

Flying higher.

Using signals that cross the coast at or near to 90°

#7. An aircraft is tracking away from an NDB on a track of 023°(T). If the drift is 8° port and variation 10° west, which of the RMIs illustrated below shows the correct indications?

Since its NDB and not VOR, aircraft variation will be used.

Variation West magnetic best hence,

True bearing 23°

magnetic = 23° plus 10°=33°

rmi shows 33° on tail

Port drift is anticipated, so to counter we steer heading to right by the same amount

ad 8° to 33° =41° compass heading is 41°

#8. The BFO facility on ADF equipment should be used as follows when an NDB having NON A1A type emission is to be used:

BFO on for tuning and identification but may be turned off for monitoring.

BFO on for tuning but can be turned off for monitoring and identification purpose.

BFO off during tuning, identification and monitoring because this type of emission is not modulated.

BFO should be switched on for tuning, ident and monitoring.

The NDBs have a 2 or 3 letter identification and there are two types of emission:

N0NA1A

N0NA2A

To make the unmodulated parts of the A1A signal audible, ADF incorporates a BFO.
Selecting the BFO on makes the N0N carrier wave audible and allows the A1A type of ident to be heard.
BFO is not needed for an A2A signal which is already modulated to an audible frequency
Hence when using N0NA1A beacons, the BFO should be selected ON for (manual) tuning, identification and monitoring.

#9. The Protection Ratio of 3:1 that is provided within the Promulgated range/Designated Operational Coverage of an NDB by day cannot be guaranteed at night because of:

Long range skywave interference from other transmitters.

Skywave signals from the NDB to which you are tuned.

The increased skip distance that occurs at night.

The possibility of sporadic E returns occurring at night.

The long ground waves of LF and MF signals mean that occasionally signals from stations on similar frequencies overlap.

This will not cause errors in the daytime if the stations are only used within the protected range.

At night, returning sky waves can cause rogue signals at considerable range producing the same problems as night effect.

The problem can be detected aurally or visually as with night effect and there should also be two station idents audible.

Some ADF equipment have a “bandpass” switch fitted to reduce the bandwidth which is received when the switch is set to SHARP.

An aircraft receiving station interference from another beacon on a similar but not identical frequency can reduce the interference by listening to a sharper band.

Because of the twin errors of night effect and station interference, and because other radio sources create more noise at night, published protected ranges are not valid in the hours of darkness.

The protected range may also be referred to as the Designated Operational Coverage (DOC).

#10. An aircraft has an RMI with two needles. Assume that: i) The aircraft is outbound from NDB Y on a track of 126°(M) drift is 140° Port. ii) A position report is required when crossing a QDR of 022 from NDB Z. Which of the diagrams below represents the RMI at the time of crossing the reporting point?

the RMI compass card is fed with magnetic heading, so the bearing shown is the magnetic bearing of the NDB.

Track is magnetic 126° magnetic track and not true track, also the RMI compass card is fed with magnetic heading, so the bearing shown is the magnetic bearing of the NDB. hence drift will not be applied (since drift in case of ndb numerical is only applied if given to the aircraft not the station)

QDR – Mag FROM station 022° from the station is depicted this way

#11. Each NDB has a range promulgated in the COMM section of the Air Pilot. Within this range interference from other NDBs should not cause bearing errors in excess of:

day ± 5

night ± 10

day ± 6

night ± 5

The accuracy of ADF is /-5° within the designated operational coverage, by day only. This refers to the measured bearing and does not include any compass error.

#12. The range promulgated in the Air Pilot and flight guides for all NDBs in the UK is the range:

Within which a protection ratio of 3:1 is guaranteed by day and night

Up to which bearings can be obtained on 95% of occasions.

Within which bearings obtained by day should be accurate to within 5°.

Within which protection from skywave protection is guaranteed.

The accuracy of ADF is /-5° within the designated operational coverage, by day only. This refers to the measured bearing and does not include any compass error.

#13. In order to resolve the 180° directional ambiguity of a directional LOOP aerial its polar diagram is combined with that of a SENSE aerial ………………………….. to produce a…………… whose single null ensures the ADF needle moves the shortest distance to indicate the correct…………….

at the aircraft, cardioid, radial.

at the transmitter, limacon, bearing.

at the aircraft, limacon, bearing.

at the aircraft, cardioid, bearing.

ADF systems use a loop shaped aerial to find the direction of an incoming signal.

When the loop is in line with the path of the radio waves the difference in phase between the signals received on the two sides of the loop causes a current to flow.

When the aerial is at right angles to the direction of travel both sides receive the same phase signal and no current flows.

If the aerial is rotated until no current flows we can therefore be sure it lies at right angles to the wave movement.

The only thing we cannot know is whether the NDB lies in front of us or behind us.

This is the ambiguity that needs to be resolved.

If we plot the value of the induced current as the aerial is rotated we find a figure of eight shape with two clearly defined null points and two less clearly defined maxima.

The diagram is a polar diagram.

The double null is the ambiguity as identified above.

To resolve the ambiguity a sense aerial is added to the system

#14. The protection ratio afforded to NDBs in the UK within the Promulgated range(DOC) applies:

by day only.

by night only.

both day and night.

at dawn and dusk.

The accuracy of ADF is /-5° within the designated operational coverage, by day only. This refers to the measured bearing and does not include any compass error.

#15. The phenomena of coastal refraction affecting ADF bearings is caused by the signal _ when it reaches the coastline and bending _ the normal to the coast:

accelerating towards

decelerating towards

accelerating away from

decelerating away from

Coastal Refraction. Radio waves speed up over water due to the reduced absorption of energy (attenuation) compared to that which occurs over land. This speeding up causes the wave front to bend (Refract) away from its normal path and pull it towards the coast.

#16. In an ADF system, night effect is most pronounced:

during long winter nights.

when the aircraft is at low altitude.

when the aircraft is at high altitude.

at dusk and dawn.

By day the D-region absorbs signals in the LF and MF bands. At night the D-region disappears allowing skywave contamination of the surface wave being used.

The effect is manifest by fading of the audio signal and the needle ‘hunting’ and is worst around dawn and dusk, when the ionosphere is in transition.

#17. When the induced signals from the loop and the sense antenna are combined in an ADF receiver, the resultant polar diagram is:

a limacon

a cardioid

figure of eight shaped

circular

#18. When flying over the sea and using an inland NDB to fix position with a series of position lines, the plotted position in relation to the aircraft’s actual position will be:

further from the coast.

closer to the coast.

co-incident

inaccurate due to the transmitted wave front decelerating.

For an aircraft flying over the sea the error puts the aircraft position closer to the coast than its actual position.

The effect can be minimised by:

Using NDBs on or near to the coast.

Flying higher.

Using signals that cross the coast at or near to 90

#19. An aircraft on a heading of 235°(M) shows an RMI reading of 090° with respect to an NDB. Any quadrantal error which is affecting the accuracy of this bearing is likely to be

a maximum value.

a very small value.

zero, since quadrantal error affects only the RBI.

zero, since quadrantal error affects only the VOR.

The theoretical reception polar diagram of the loop aerial is distorted by the airframe which produces a strong electrical field aligned fore and aft. Incoming NDB signals are thus refracted towards the fore and aft airframe axis. The maximum refraction occurs in the quadrants ,on relative bearings of 045°, 135°, 225° & 315°

#20. The principal propagation path employed in an NDB/ADF system is:

skywave

surface wave

direct wave

ducted wave

Since the mode of propagation used is surface wave, most NDBs will be found between about 250 and 450 kHz.

#21. The ADF of an aircraft on a heading of 189°(T) will experience the greatest effect due to Quadrantal Error if the NDB bears:

234°(T)

279°(T)

225°(T)

145°(T)

Finish

Results

#1. The phenomenon of coastal refraction which affects the accuracy of ADF bearings:

#2. An aircraft is intending to track from NDB ‘ A’ to NDB ‘B’ on a track of 050° (T), heading 060° (T). If the RBI shows the relative bearing of ‘ A’ to be 180° and the relative bearing of ‘B’ to be 330° then the aircraft is:

#3. ADF Quadrantal Error is caused by:

#4. The overall accuracy of ADF bearings by day within the Promulgated Range (DOC) is:

#5. In order to Tune, Identify and Monitor NON A1A NDB emissions the BFO should be used as follows:

#6. The magnitude of the error in position lines derived from ADF bearings that are affected by coastal refraction may be reduced by:

#7. An aircraft is tracking away from an NDB on a track of 023°(T). If the drift is 8° port and variation 10° west, which of the RMIs illustrated below shows the correct indications?

#8. The BFO facility on ADF equipment should be used as follows when an NDB having NON A1A type emission is to be used:

#9. The Protection Ratio of 3:1 that is provided within the Promulgated range/Designated Operational Coverage of an NDB by day cannot be guaranteed at night because of:

#11. Each NDB has a range promulgated in the COMM section of the Air Pilot. Within this range interference from other NDBs should not cause bearing errors in excess of:

#12. The range promulgated in the Air Pilot and flight guides for all NDBs in the UK is the range:

#14. The protection ratio afforded to NDBs in the UK within the Promulgated range(DOC) applies:

#15. The phenomena of coastal refraction affecting ADF bearings is caused by the signal _______ when it reaches the coastline and bending _______ the normal to the coast:

#16. In an ADF system, night effect is most pronounced:

#17. When the induced signals from the loop and the sense antenna are combined in an ADF receiver, the resultant polar diagram is:

#18. When flying over the sea and using an inland NDB to fix position with a series of position lines, the plotted position in relation to the aircraft’s actual position will be:

#19. An aircraft on a heading of 235°(M) shows an RMI reading of 090° with respect to an NDB. Any quadrantal error which is affecting the accuracy of this bearing is likely to be

#20. The principal propagation path employed in an NDB/ADF system is:

#21. The ADF of an aircraft on a heading of 189°(T) will experience the greatest effect due to Quadrantal Error if the NDB bears:

#15. The phenomena of coastal refraction affecting ADF bearings is caused by the signal _ when it reaches the coastline and bending _ the normal to the coast: