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shorehamite
1st Sep 2022, 17:53
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?

Whopity
1st Sep 2022, 18:49
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.

shorehamite
1st Sep 2022, 19:38
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.

Whopity
2nd Sep 2022, 13:03
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.

Edward Hawkins
2nd Sep 2022, 18:54
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.

ea200
2nd Sep 2022, 20:30
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.

jonkster
3rd Sep 2022, 00:00
https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/261x394/compass_correction_card_afm_51_37_figure_1_15_63daa9c7018ace 6bd8e59a4d1b6a79f7e64b75e3.png

gerpols
3rd Sep 2022, 09:28
Above is a deviation card required in the cockpit after a compass swing. It`s not a variation card ..:ok:

ea200
3rd Sep 2022, 09:49
Above is a deviation card required in the cockpit after a compass swing. It`s not a variation card ..:ok:

Exactly, and if the deviation is as described in post 3 that compass certainly needs a swing!

Fl1ingfrog
3rd Sep 2022, 11:27
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.

BigEndBob
6th Sep 2022, 09:57
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.

BigEndBob
6th Sep 2022, 10:00
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.

BigEndBob
6th Sep 2022, 10:04
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.

fitliker
6th Sep 2022, 14:41
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 ;
Questions answered fifty bucks
correct answers one hundred
dumb looks are still free ,

rudestuff
6th Sep 2022, 15:22
VDMONA is simple... I thought a mnemonic was supposed to mean something - like "Cadburys Dairy Milk Very Tasty"

Edward Hawkins
6th Sep 2022, 19:06
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.

Fl1ingfrog
7th Sep 2022, 07:56
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.

BigEndBob
7th Sep 2022, 18:22
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?

We know all about CDMVT.

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!

Fl1ingfrog
7th Sep 2022, 19:21
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?

BEagle
7th Sep 2022, 22:08
"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....

shorehamite
8th Sep 2022, 10:28
The other really annoying question that has come up relates to a flight to France, the need to calculate flight time and work out departure and arrival times with many references to UTC, but then
they give the possible answers in British Summer Time!! Grrrrr.

TheOddOne
8th Sep 2022, 16:41
That's just to make sure the student is paying attention. Apparently there are several answers given in units which might trap the unwary, be prepared to convert answers to different units/times.
I think this is justified where we commonly have have American training aircraft with a POH in lbs, statute mph and US Gallons yet we dispense fuel in litres and the CAA quote MTOM on G-INFO in Kg. We also refer to vertical distances in feet, short horizontal distances in metres/kilometres (runway lengths/visibility) and long navigational distances in Nautical Miles.
If a student isn't adept at being agile with all these units (and the use of the whizz wheel to resolve them all) they're going to come a cropper out there.

Remember the Gimli Glider

TOO

BigEndBob
8th Sep 2022, 19:27
Also another school asked if i could set exam on our system for one of their students.
We could find no way for the candidate to enter a request and register to do exam at our school via his ePortal.
There needs to be an add button.
We gave up.