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exam wording

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exam wording

1st Sep 2022, 18:53

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exam wording

One or two students have commented on strange wording in the PPL nav exam,
the question is worded.......... ...........and the deviation is minus 5 degrees west.
I always thought west was best, any ideas?
1st Sep 2022, 19:49

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Do you mean Deviation or Variation. Either way from AP3456
Variation is measured in degrees and is named East (+) or West (–) according to
whether the North-seeking end of a freely-suspended magnetic needle, influenced only by the Earth’s
field, lies to the East or West of True North at any given point.
A useful mnemonic is:
"Variation East, Magnetic least,
Variation West, Magnetic best."
For Deviation:
The angular difference between the direction of Magnetic North and that of Compass North,
and therefore all Magnetic directions and their corresponding Compass directions, is called
Deviation. Deviation is measured in degrees and is named East (+) or West (–) according to
whether the North-seeking end of a compass needle,under various disturbing influences, lies to
the East or West of Magnetic North.
I have always used + East and - West.

Last edited by Whopity; 1st Sep 2022 at 20:34.
1st Sep 2022, 20:38

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The question was along the lines of:-
if the compass heading is 180 degrees and the deviation is minus 5 degrees west, what is the magnetic heading.
2nd Sep 2022, 14:03

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That assumes that you have a True Compass, not very common in GA! If the Compass was Mag then the heading would be 180 as stated, but presumably if its True, the Mag heading will be 185. The minus being taken from Mag to achieve True. or as you said West is best! Not a very well thought out question.
2nd Sep 2022, 19:54

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If the compass heading is 180 degrees and the variation is 5 degrees west then the magnetic heading will be 175 degrees. Remember error west compass best, error east compass least. This seems a quite straightforward question. If you then needed the true heading you would apply variation to the magnetic heading.
2nd Sep 2022, 21:30

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It seems to me that there is a lot of confusion on this thread about the difference between Deviation and Variation. If you understand the difference then the question in post 3 is pretty clear. Refer to Whopity's posts.
3rd Sep 2022, 01:00

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3rd Sep 2022, 10:28

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Above is a deviation card required in the cockpit after a compass swing. It`s not a variation card ..
3rd Sep 2022, 10:49

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Originally Posted by gerpols
Above is a deviation card required in the cockpit after a compass swing. It`s not a variation card ..
Exactly, and if the deviation is as described in post 3 that compass certainly needs a swing!
3rd Sep 2022, 12:27

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It seems to me that there is a lot of confusion on this thread about the difference between Deviation and Variation. If you understand the difference then the question in post 3 is pretty clear.
OK, back to basics then;
Maps and charts are produced with reference to true north/south, because this doesn't changes.

Variation is global and relates to the earths magnetic field (flux) however owing to the earths rotating wobble it is continuously moving side to side East to West/West to East. A magnetic compass aligns itself with the earths magnetic flux not the True North/South poles around which the earth is said to rotate. The angle of difference can be measured but it varies (variation) depending on where you are on the earth. On the chart, be it the 1:500,000 or the 1:250,000 version, they overprint it with a dashed 'Isogonal' line. At any point along the line the variation is the same. This makes it straightforward for the pilot to plot. As the flight progresses it is necessary to update the magnetic variation value from the chart Isogonals and the magnetic compass heading should be revised for each sector.

Deviation, that concerns a pilot, is a local problem; in the aeroplane electrical circuits such as wiring looms and equipment in particular are the culprits. Don't put anything that is magnetic near the compass. A 'compass swing' (see the compass card example above) is done with the engine running and all electrical equipment switched on. Before starting the engine and switching the master switch on note the compass indication. After starting and switching on the electrics see the difference in the compass. Incidentally, a walker needs to be aware that the surface itself may magnetically be deviating, in localised patches, and will change the compass needle. Deviation then can be described as a corruption of the needle swing but this effect can be known, measured and recorded.

Last edited by Fl1ingfrog; 3rd Sep 2022 at 14:19.
6th Sep 2022, 10:57

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Yes i have seen that question, candidate called me in to clarify, i said bad English.
These exams are becoming a nightmare, the feed back only giving area where the question was wrong is useless.
What if the answer set is wrong, happened many times on the old paper system.

I scanned aircraft general after student sat exam, i could not see any wrong answers, yet two were failed.
Now we have no idea why that person failed, the ref. is too vague.
6th Sep 2022, 11:00

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Originally Posted by Fl1ingfrog
OK, back to basics then;
Maps and charts are produced with reference to true north/south, because this doesn't changes.

Variation is global and relates to the earths magnetic field (flux) however owing to the earths rotating wobble it is continuously moving side to side East to West/West to East. A magnetic compass aligns itself with the earths magnetic flux not the True North/South poles around which the earth is said to rotate. The angle of difference can be measured but it varies (variation) depending on where you are on the earth. On the chart, be it the 1:500,000 or the 1:250,000 version, they overprint it with a dashed 'Isogonal' line. At any point along the line the variation is the same. This makes it straightforward for the pilot to plot. As the flight progresses it is necessary to update the magnetic variation value from the chart Isogonals and the magnetic compass heading should be revised for each sector.

Deviation, that concerns a pilot, is a local problem; in the aeroplane electrical circuits such as wiring looms and equipment in particular are the culprits. Don't put anything that is magnetic near the compass. A 'compass swing' (see the compass card example above) is done with the engine running and all electrical equipment switched on. Before starting the engine and switching the master switch on note the compass indication. After starting and switching on the electrics see the difference in the compass. Incidentally, a walker needs to be aware that the surface itself may magnetically be deviating, in localised patches, and will change the compass needle. Deviation then can be described as a corruption of the needle swing but this effect can be known, measured and recorded.

What of the word "minus".

We know what 5 west deviation means. We know it's been added on to magnetic hdg. to get compass.

But why the word minus.
6th Sep 2022, 11:04

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Originally Posted by Edward Hawkins
If the compass heading is 180 degrees and the variation is 5 degrees west then the magnetic heading will be 175 degrees. Remember error west compass best, error east compass least. This seems a quite straightforward question. If you then needed the true heading you would apply variation to the magnetic heading.
But why the word minus.

I think the person setting exam wrote the answer in the question by mistake.
6th Sep 2022, 15:41

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VDMONA is simple way of remembering the more common compass errors
Variation
Deviation
Oscillation
Magnetic dip
Northerly Southey turning errors
Acceleration Deceleration errors
Compass swings are used to help compensate for installation errors , Some freight can make your compass do interesting things . Flying low level the compass will spin like a spinning top over some mineralization areas ( large Gold bearing quartz deposits) .
My favourite AME had a sign over his desk ;
dumb looks are still free ,
6th Sep 2022, 16:22

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Originally Posted by fitliker
VDMONA is simple...
I thought a mnemonic was supposed to mean something - like "Cadburys Dairy Milk Very Tasty"
6th Sep 2022, 20:06

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Originally Posted by rudestuff
I thought a mnemonic was supposed to mean something - like "Cadburys Dairy Milk Very Tasty"
That's correct; or the other way round True Virgins Make Dull Company. I learned both of these over 50 years ago. Another good one is CADET: draw an arrow above the word from the C to the T, then underline the three letters in the middle. You then get Compass to True Add East. This + and - for deviation seems unique to aircraft navigation, I never encountered this as a navigator at sea. The question gives both descriptions for deviation i.e. minus and west.
7th Sep 2022, 08:56

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I can only think that the + and - thing is mistakenly taken from the common ADF techniques that are taught and then applied inappropriately to deviations of the compass. You cannot calculate deviation of the compass because the errors will only be discovered by undertaking the 'swing'. Each installation will be different. The swing will not be consistent around the clock but must be able to be countered with adjustable magnets that are built into the compass and this is not predictable prior to the swing.
7th Sep 2022, 19:22

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The problem is the use of the word "Minus".

The question should be;
If the compass heading is 180 degrees and the deviation is 5 degrees west, what is the magnetic heading?

And every single aircraft i have operated i have had to go out to the runways and do my own compass swing.

I even had one aircraft returned to me from maintenance with compass 40 degrees off.
Supposedly new compass and swung...with no radios fitted!
7th Sep 2022, 20:21

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If the compass heading is 180 degrees and the deviation is 5 degrees west, what is the magnetic heading?
As all compass headings must be magnetic, then may I suggest:

If the corrected/rectified compass heading is 180 degrees and the deviation is 5 degrees west, what is the uncorrected compass heading?
7th Sep 2022, 23:08

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"If your calculated magnetic heading is 180° and the aircraft's compass deviation card shows 5° West, what compass heading do you need to set in order to fly the calculated heading?"

Now turn it round....