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While flying on a magnetic heading of 193°(M) in the northern hemisphere, an aircraft measures the relative bearing of ‘ONO’ NDB on an RBI Relative Bearing Indicator as 063°R. Given the following information, what bearing should be plotted from the beacon to the aircraft on a Lambert chart?

Variation at the aircraft: 6°E 
Variation at the station: 4°E 
Chart convergence between the aircraft and the NDB: 8°

  • A

    074° (T)

  • B

    082° (T)

  • C

    068° (T)

  • D

    076° (T)

Refer to figure.
Converting a Relative Bearing (RBI) into a True Bearing:

Apply aircraft variation to the magnetic heading to get true heading.

Bearings measured at ground station (VOR, VDF) - variation at ground station 
Bearings measured at aircraft (NDB/ADF, AWR) - variation at aircraft

True Heading 
(T)
Variation 
(V)
Magnetic Heading (M)Deviation 
(D)
Compass Heading 
(C)
199°6°E193°  

Add relative bearing to true heading in order to get true bearing TO the station. If the answer comes to more than 360°(T), subtract 360.

Take the reciprocal in order to get the True Bearing to plot FROM the station.

QUJ = RBI + True Heading 
QTE = RBI + True Heading - 180°

The exercise is asking us for a true bearing from the beacon to the aircraft (QTE):

QUJ= 63° + 199° = 262°
QTE = 63° + 199° - 180° = 82°

Now to apply the convergency. 
The chart convergence here means that we can not just plot the reciprocal heading from an NDB, as this would give us a false position, as shown in the figure above.

We have to account for the 8° convergency, and to work out how to do this, the best way is often to use a diagram like the one above, and note that the red angle is smaller at the NDB than the same angle would be at the aircraft, so therefore the red angle is 8° smaller than the reciprocal bearing of 082°. This can also be done without drawing if you are adept at using the DIID method, but be careful, that way is much easier to make a mistake.

True bearing to be plotted from the NDB to the aircraft = 082° - 8° = 074°

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