VOR, ADF, DME & Bearings

B. 044°

MH = 270 - 2 = 268; QDM = MH + RB = 268 + 316 = 584 - 360 = 224; QDR = QDM +/- 180 = 044.

A. AM, FM, anti-clockwise

In a Doppler VOR the reference signal is amplitude modulated, the bearing (variable) signal is frequency modulated and its rotation is anti-clockwise.

A. 123 NM

Range = 1.23 (sqrt h_aircraft + sqrt h_station) = 1.23 x 100 = 123 NM (1.25 is sometimes used: 125 NM).

A. local thunderstorm activity

A Cb is a huge source of LF/MF static and can swing the ADF needle towards itself - the largest single error. Coastal refraction and quadrantal error are smaller and predictable.

The question was recalled without its options; these options were written to it.

A. +/- 5

By day, within the published range, ADF bearings should be accurate to +/- 5 deg.

C. the station; the aircraft

A VOR radial is measured at the station against magnetic north there; an ADF bearing is measured at the aircraft (heading + RB) with the aircraft's compass.

The question was recalled without its options; these options were written to it.

B. 190-1750 kHz

NDBs use LF/MF, 190-1750 kHz (the ADF receiver tunes the same band). 108-117.95 MHz is VOR/ILS localiser.

The question was recalled without its options; these options were written to it.

C. secondary, 962-1213 MHz, UHF

The aircraft interrogates and the ground beacon replies (secondary radar), on UHF channels between about 960 and 1215 MHz - roughly 1000 MHz.

The question was recalled without its options; these options were written to it.

B. 11.7 NM

Height = 36,000 / 6076 = 5.9 NM. Slant range = sqrt(10^2 + 5.9^2) = 11.6 NM. Slant-range error is small once the range exceeds about 3 x height in thousands of feet.

The question was recalled without its options; these options were written to it.

B. omni-directional

The NDB radiates equally in all directions; the direction-finding is done in the aircraft by the ADF loop and sense aerials.

The question was recalled without its options; these options were written to it.

A. 050 and 230

QDM = MH + RB = 040 + 010 = 050 (bearing TO the beacon); QDR = 230 (from it).

C. resolve ambiguous bearings.

The loop gives a bearing with 180 deg ambiguity; the sense aerial lets the ADF decide which of the two it is.

A. Signal bending by a/c metallic surface

Quadrantal error is caused by the aircraft structure re-radiating (bending) the signal.

A. switch the BFO on

A1A keying has no audio tone; the beat frequency oscillator mixes with the carrier to make it audible. NON/A2A beacons need no BFO for the ident.

B. surface wave

LF/MF signals follow the earth's curvature as surface waves; sky waves at night cause night effect.

The question was recalled without its options; these options were written to it.

C. the beacon is near the coast and the aircraft at high altitude

Use a beacon close to the coast, a bearing that crosses the coast at about 90 deg, and fly high (the error falls with height).

A. 6 from centerline

On a VOR indicator each dot is 2 deg, so 3 dots is 6 deg off the selected radial.

A. 6mins

Relative bearing going from 45 to 90 deg: the distance flown equals the distance abeam, so the time to the station from abeam equals the 6 minutes flown.

A. 2 nm

Overhead the station the DME reads slant range = height: 12,000 ft = about 2 NM.

B. great circle

Radio waves follow great circle paths (the shortest route).

A. 130

QDM = 060 + 030 = 090, so the aircraft is on QDR 270. The inbound track for QDR 250 is 070; the aircraft is north of it, so turn right of 070 by 60: heading 130.

C. 30.2 nm

Height 24,380 ft = 4.0 NM. Slant range = square root of (30 squared + 4.0 squared) = 30.3 NM, so the indicated range is about 30.2-30.3 NM.

B. 100 aircraft (about 2700 pulse pairs per second)

A beacon can answer about 2700 pulse pairs a second - roughly 100 aircraft. Beyond that it reduces its receiver sensitivity and ignores the weakest (furthest) interrogators.

The question was recalled without its options; these options were written to it.

B. ±5°

VDF class A is +/- 2 deg, class B +/- 5 deg, class C +/- 10 deg.

A. 190-1750 kHz

NDBs/locators use 190-1750 kHz (VOR is 108-117.95 MHz).

C. 3.5 Nm

One degree of error at 200 NM = 200 x tan 1 deg = 3.5 NM (1-in-60 rule gives about 3.3 NM).

C. to, 3 dot fly left

The deviation indication depends only on position relative to the selected radial, not on heading, so turning to the reciprocal changes nothing: TO, 3 dots left.

C. There will be no change in VOR CDI Indications

A VOR/CDI shows the aircraft's position relative to the selected radial; it does not depend on the aircraft's heading, so turning the aircraft changes nothing.

A. 22 NM of the VOR

MOCA gives obstacle clearance on the whole segment but guarantees VOR signal coverage only within 22 NM (25 SM) of the VOR. MEA guarantees both for the whole segment.

The question was recalled without its options; these options were written to it.

A. magnetic

The VOR needle shows the magnetic bearing to the station derived from the VOR signal itself, so card deviation does not affect it (the ADF needle, which is relative bearing added to the card, would carry the deviation).

The question was recalled without its options; these options were written to it.

A. +/- 0.25 NM + 1.25 % of range

ICAO DME/N system accuracy: +/- 0.25 NM plus 1.25 % of the distance measured.

The question was recalled without its options; these options were written to it.

B. a figure of eight; a cardioid

The loop gives a figure of eight with two nulls (180 deg ambiguity); adding the omni-directional sense aerial gives a cardioid with a single null, resolving the ambiguity.

The question was recalled without its options; these options were written to it.

A. the one at a higher pitch, heard once

In each 30-40 s cycle the VOR identifies three times at 1020 Hz and the DME once at a higher tone (1350 Hz).

The question was recalled without its options; these options were written to it.

A. 30° port

With ADF reading 190 the aircraft is 10 deg off track (track error). After 90 of 140 NM, closing angle = 10 x 90/50 = 18 deg; the total correction is about 30 deg, to port (the aircraft is right of track).

A. inland and the bearing crosses the coast at an acute angle

Coastal refraction is worst when the bearing crosses the coastline at a shallow (acute) angle and the NDB is inland; at right angles there is no refraction error.

C. 155

Phase difference = reference - variable = 110 - 315 = -205; add 360: 155. Always reference minus variable.

The question was recalled without its options; these options were written to it.

B. 270 with TO

Set the course you are flying: 270, and the flag reads TO. The CDI then deflects towards the radial - fly towards the needle. With 090 set you would get reverse sensing.

B. the selected course, if flown, would take the aircraft towards the station (the radial the aircraft is on is within 90 deg of the reciprocal of the OBS)

TO/FROM depends only on the aircraft's position relative to the OBS course line through the station, never on heading. Abeam the station (90 deg to the course) the flag changes over.

C. 120

North of an easterly radial, the radial lies to your right (south): turn right of the course by 30 deg - heading 120 - and turn onto 090 as the CDI centres.

A. 6 deg port

Heading = QDM - RB (as 354 = -6) = 045 + 6 = 051. Steering 6 deg right of track to hold it means the wind is from the right and the drift is 6 deg PORT.

A. 094

Radials are magnetic bearings FROM the station. The QDM is the reciprocal: 094(M). Variation only matters when converting to true.

The question was recalled without its options; these options were written to it.

D. at dusk and dawn

Night effect is sky-wave contamination as the ionosphere changes; it is worst when the D layer is forming or disappearing - around sunrise and sunset.

The question was recalled without its options; these options were written to it.

D. 3.7 %

2500 / (11.1 x 6076) = 0.037 = 3.7 %.

The question was recalled without its options; these options were written to it.

B. 5.8 NM

Overhead, the slant range is just the height: 35,000 / 6076 = 5.8 NM.

The question was recalled without its options; these options were written to it.

A. an FM reference signal and an AM variable signal

Conventional VOR: reference 30 Hz carried as FM on a 9960 Hz subcarrier; variable 30 Hz AM produced by the rotating pattern. Doppler VOR reverses them.

The question was recalled without its options; these options were written to it.

B. offset (teardrop)

Measure the arrival heading against the inbound track: 250 - 090 = 160 deg. Right-hand hold: within -70 to +110 deg is direct, +110 to +180 offset (teardrop), +180 to +290 parallel. 160 falls in the offset sector.

C. QTE is 353 +/- 5

A bearing passed by a VDF station is a true bearing from the station (QTE). Class B accuracy is +/- 5 deg, so QTE 353 +/- 5. (QDR would be 345 magnetic and class A is +/- 2.)

A. 285 TO

To track inbound along the 105 radial the aircraft flies 285; the OBS is set to the inbound course, 285, with a TO flag.

A. 080

An easterly wind gives port drift, so heading = 010. The abeam station bears 090(T) from the aircraft: RB = 090 - 010 = 080.

The question was recalled without its options; these options were written to it.

C. 6 NM left of track

4 dots x 2 deg = 8 deg off. Fly-right means the track is to your right, so you are LEFT of it: 45 x 8 / 60 = 6 NM.

The question was recalled without its options; these options were written to it.

B. 10 deg or more

Full scale = 5 dots x 2 deg = 10 deg; the needle cannot show more, so it means "10 or more".

The question was recalled without its options; these options were written to it.

B. 145

Bearing to the feature = 355 - 30 = 325(M); from the feature to the aircraft is the reciprocal, 145(M) - the line you plot from the feature.

The question was recalled without its options; these options were written to it.

A. 1 deg

The monitor checks a fixed radial; a shift of more than 1 deg (or loss of modulation) makes it remove the ident/transmission or change over to the standby.

C. 221°

Magnetic bearing to the NDB = magnetic heading + relative bearing = 311 + 270 = 581 - 360 = 221. Drift does not enter.

D. 161°

Magnetic bearing to the station = 075 + 270 = 345; true = 345 - 4 = 341; from the station the aircraft is on 161.

A. 88 NM

Time to station = time for the bearing change x 60 / degrees changed = 5.5 x 60 / 10 = 33 min. Distance = 160 x 33 / 60 = 88 NM.

The question was recalled without its options; these options were written to it.

B. 275 deg

A TO flag with OBS 090 puts the aircraft west of the station (radial about 270). Half-scale deflection to the right is about 5 deg: the aircraft is on the 275 radial.

B. from a line parallel to the aircraft's meridian, drawn through the NDB

An ADF bearing is measured at the aircraft against the aircraft's meridian. Draw that meridian's direction through the NDB and plot the reciprocal from it; on a Lambert the straight line then approximates the great circle.

Our independent check found that more than one option can be argued for, as worded in the recall. The key gives the answer most references support.

The question was recalled without its options; these options were written to it.

B. 30° starboard

ADF 170 on a track of 090 puts the aircraft 10 deg left of track; after 90 of 135 NM the closing angle is 10 x 90/45 = 20, so the total correction is 30 deg to starboard.

A. 068 and 248

Track = heading + starboard drift = 065(T); magnetic = 065 + 3W = 068(M). Flying TO the station, the magnetic track is the QDM: 068; the QDR (from the station) is the reciprocal, 248.

A. 244

QDR = 047 + 180 = 227(M); true = 227 + 17 (east) = 244 = QTE. (QUJ, true bearing TO the station, would be 064.)

The question was recalled without its options; these options were written to it.

B. Short distance

Homing (keeping the ADF needle on the nose) curves the track downwind, so it is only practical over short distances.

C. 180 TO

North of the VOR on the 360 radial the inbound leg is flown on 180 TO.

As recalled, this question depended on a chart or table that is not reproduced here; the key is the recalled paper's answer.

C. 133Nm

Range = 1.23 (sqrt 8000 + sqrt 325) = 1.23 (89.4 + 18.0) = 132 NM.

A. 170 and tail 350

RMI pointer = heading + relative bearing = 190 + 340 = 530 - 360 = 170; the tail is 350.

B. 130

The aircraft is on the 310 (magnetic) radial from the VOR (320 T - 10 E variation). To centre the needle with a TO flag the OBS is set to the reciprocal, 130.

A. Pointer reads 170 & tail reads 350

RMI pointer shows the magnetic bearing to the station = heading + relative bearing = 340 + 190 = 530 - 360 = 170; the tail reads the reciprocal, 350.

B. Beacon inland at an acute angle to coast

Coastal refraction bends the signal where it crosses the shoreline obliquely, so the error is worst when the bearing crosses the coast at a shallow (acute) angle; at 90 deg there is none.

C. 30 sec

A DME ident is transmitted once every 30 seconds (the associated VOR three times in that period).

C. 130°/045°

Present QDM = 170 + 345 - 360 = 155, so the aircraft is on the 335 radial, west of the 355 radial. Inbound on the 355 radial is QDM 175. A 45 deg intercept means heading 175 - 45 = 130, and on intercept the relative bearing is 175 - 130 = 045.

C. VHF

VOR operates at 108-117.95 MHz, in the VHF band.

B. left with "TO" showing

The aircraft is on radial 120, northeast of the 150 reference radial of course 330: needle left, TO flag.

B. multipath reflections from terrain and buildings

Reflected signals mix with the direct one and make the CDI needle wander rhythmically (scallop) along the radial.

The question was recalled without its options; these options were written to it.

A. 1 min at or below 14,000 ft, 1.5 min above

PANS-OPS: 1 minute at or below 14,000 ft, 1 minute 30 seconds above 14,000 ft (adjusted for wind).

The question was recalled without its options; these options were written to it.

A. in search mode, not yet locked on

Until it recognises its own replies, the interrogator searches and the counters run; once locked on (track mode) a steady range is shown.

B. 155(T)

Bearing to the island = 345 - 30 = 315(M) = 335(T) (east variation added). Plot the reciprocal from the island: 155(T).

The question was recalled without its options; these options were written to it.

A. 255

The aircraft is due west of the VOR: true bearing FROM the station 270. Radials use the station's variation: 270 - 15 E = 255.

A. +/- 4 deg

With both receivers tuned to the same VOR, the bearings must agree within 4 deg; a ground checkpoint allows +/- 4 deg, an airborne checkpoint +/- 6 deg.

Our independent check could not confirm this answer from the official sources we hold; treat it with care and confirm with your instructor.

The question was recalled without its options; these options were written to it.

A. 316

A QTE is a great-circle bearing; a Mercator straight line is a rhumb line. Apply the conversion angle (half convergency = 1 deg) towards the equator: the great circle lies on the pole side, so the rhumb line from B is 1 deg nearer north: 316.

B. a large reduction in site error

The wide-aperture aerial ring of a DVOR is much less affected by reflections near the site, so site error is greatly reduced.

The question was recalled without its options; these options were written to it.

B. greater from the 50 NM beacon

The same angular error produces a bigger lateral error the further the beacon is from the aircraft.

The question was recalled without its options; these options were written to it.

A. 97 NM

Distance flown = GS x time = 290 x 20/60 = 97 NM; the bearings do not change that.

A. 3.5 NM

200 x tan 1 = 3.5 NM (1 in 60: 200/60 = 3.3).

The question was recalled without its options; these options were written to it.

B. 16,000 ft

175 = 1.23 (sqrt 196 + sqrt h) = 1.23 (14 + sqrt h): sqrt h = 128, h = 16,400 ft - about 16,000.

The question was recalled without its options; these options were written to it.

B. closer to the coast

Coastal refraction bends the wave towards the coast, so position lines plotted from it put you closer to the coast than you really are.

The question was recalled without its options; these options were written to it.

C. accelerates; away from

Over water the surface wave travels faster, so it bends away from the normal (towards the coastline) - the bearing appears displaced towards the coast.

The question was recalled without its options; these options were written to it.

A. 1.5 dots right

The needle shows where the course is: 3 deg off = 1.5 dots, on the right (fly right).

The question was recalled without its options; these options were written to it.

B. QTE 358 +/- 5

True bearing from the station is the QTE; class B is +/- 5 deg. (QDM would be 178 + 7 = 185, QUJ 178.)

As recalled, this question depended on a chart or table that is not reproduced here; the key is the recalled paper's answer.

The question was recalled without its options; these options were written to it.

A. 150

Bearing to the station = heading + relative bearing = 090 + 060 = 150.

The question was recalled without its options; these options were written to it.

B. phase comparison

VOR bearing is measured by phase comparison of the reference and variable signals.

B. 10 seconds

A VOR transmits its identification in Morse (or voice) at least once every 10 seconds, so a pilot can confirm the station before using it.

A. FL 60

Line-of-sight range = 1.25 (sqrt H + sqrt h), H and h in feet. 113 = 1.25 (sqrt H + 13), so sqrt H = 77.4 and H = about 6,000 ft: FL60. FL50 would give only about 105 NM.

C. 160°

Relative bearing 330: magnetic bearing to the feature = 355 - 30 = 325; true = 340; the true bearing of the aircraft from the feature is the reciprocal, 160.

B. 083

Inbound magnetic track 090 at the VOR = 085(T). Starboard drift 10: heading 075(T). Convert with the AIRCRAFT's variation: 075 + 8 = 083(M).

B. 324 TO

Inbound on the 144 radial means tracking 324 (the reciprocal) towards the station: set 324, TO. Radials are already magnetic - the variation does not enter.

The question was recalled without its options; these options were written to it.

A. 278

130 - 15 = 115(M) to the island; - 17 W = 098(T). From the island: 278(T).

B. are more than 600 m apart but serve the same location

Co-located beacons share the same ident. A last letter Z marks an associated pair that is separated (more than about 600 m) but serves the same place.

The question was recalled without its options; these options were written to it.

B. rotating the radiation pattern at 30 revolutions per second

The limacon pattern rotates 30 times a second (1800 rpm), so a fixed receiver sees a 30 Hz amplitude modulation whose phase depends on its bearing.

The question was recalled without its options; these options were written to it.

B. more accurate, best when the range circles cut at about 90 deg

DME ranges are accurate to a fraction of a mile at any distance, whereas a VOR bearing error grows with range; two good DME cuts give the best fix.

B. a curve that ends with the aircraft heading into wind near the beacon

Homing points the nose at the beacon all the time; the wind blows the aircraft sideways, the heading keeps changing, and the path curves until it arrives roughly into wind. Tracking (heading off for drift) gives a straight path.

B. its pulse pairs are sent at a random (jittered) rate and it looks for replies with the same pattern

All aircraft on the channel share frequencies. Each interrogator jitters its pulse-pair timing; only replies that keep the same spacing after each interrogation are accepted (stroboscopic lock-on).

B. select the radial or track against which the CDI shows deviation

The OBS sets the course: the CDI then shows displacement from that radial and the TO/FROM flag shows whether that course leads to or from the station. Heading has nothing to do with it.

B. offset (teardrop)

ICAO sectors: 1 = parallel entry, 2 = offset (teardrop) entry, 3 = direct entry.

A. 080 and 010

Starboard drift: steer left of track, heading 080. The beacon is on track ahead, 10 deg right of the nose: RB 010.

A. 105

The aircraft is on QDR 270, north of the inbound track 060 (which comes from QDR 240). Turn right of the required track by 45 deg: 060 + 45 = 105, then turn onto 060 as the ADF reads 315 (45 left).

A. radiates omni-directionally and provides range only

The beacon answers interrogations from all directions with an omni-directional aerial; it gives slant range, no bearing.

B. flying away from the NDB with it directly behind

Relative bearing 180 = the beacon is on the tail: the aircraft is flying away from it (QDR = heading).

D. coastal refraction

Coastal refraction bends LF/MF surface waves - an ADF error. VOR (VHF line of sight) suffers site, propagation/scalloping and equipment errors.

B. do not change - VOR indications do not depend on heading

The VOR receiver uses only the radial the aircraft is on and the OBS setting; heading never enters. What changes is whether "fly toward the needle" is still correct - flying the opposite way gives reverse sensing.