G'day Bob, Richard and fellow Aviators.

Bob I have to hand it to you, you have explained the differences between US and Australian Navigation well on Page 3.6 (issue 3 2009 BTCPLNAV) in terms of the words Course (US) and Track (Australia) both appearing to mean the same thing (path relative to the ground).

Also you make the point on the same page, that it is "JUST AS valid to change track and wind to magnetic BEFORE (caps mine) the calculation, given a magnetic heading for the answer. This is the method we shall adopt."

If you don't mind me asking so, WHY is this so? (I have also noticed the difference with US Pre Flight planning info having a True Course on a flight plan), given that the E6B computers that most of us use here in Australia are in fact American, and have a formula that one is supposed to use written on them that being:

TC (True Course) -L or + R WCA (Wind Correction Angle) = TH (True Heading) -E or +W VAR (Magnetic Variation)=MH (Magnetic Heading) -E or +W DEV (Compass Deviation)= CH (Compass Heading - the operational bit

Now the problem I am specifically having is two fold:

1) now that we are doing calcs another way I keep "tripping over" the legend on the E6B
2) when I go through the excercise table in Excercise N9 on page 3.8 my answers vary from those quoted, which is not helping my self esteem or navigational confidence, unless the one I singled out with a vengeance is erronious?

The Question I am focusing on (but having pains with) using the US formula above this time (as per the front face of the APR E6B flight computer I am using, in attempting to find the two answers of MAGNETIC HEADING that should be flown as well as the GROUND SPEED to expect (are you sure the two ways US vs Australia) both achieve exactly the same thing (excuse my naivety here)?

So I take the following details I have on Q5:

FPT of 260 deg M
VAR of 5 deg East
Forecast Wind deg True / kt 300deg TRUE /30kt
TAS 130 Kt

I then follow the instructions on the E6B VERBATIM:

1. SET WIND DIRECTION OPPOSITE (true index)
2. MARK W (Wind Dot) UP FROM G (Grommet)
3. PLACE TRUE COURSE UNDER(True Index)
4. SLIDE THE AIRSPEED UNDER W (Wind Dot)
5. READ GROUND SPEED UNDER G (Grommet)
6. READ WCA UNDER W (Wind Dot)
7. COMPLETE PROBLEM BY USE OF FORMULA (Quoted above in text)

So With my trusty E6B I: (steps to correspond with above manufacturer steps - this is the E6B that King Schools / Cessna Pilot Centers use as a preferred computer)

1) first of all line up the wind on 300 deg true, and

2) draw a line straight up from the "wind dot" which is 30 knots high, and place both a small cross (centre of cross is exactly at 30 kts) and also a line to join the cross with the dot. (so that gives me my 30 knots at 300 deg)

3) I now rotate the bezzle on my computer until the TRUE course is under (so to get the TRUE course from the FPT (260 deg mag) I simply adjust the FTP by - 5 deg VAR (since east is least) which brings my TRUE Course to 255 deg (TRUE) so I twist this course into the dial of the E6B.

4) Now I "slide the true airspeed under W (Wind Dot - in my case the centre of the cross is now sitting on the supplies TAS of 130)

5) I now read the groundspeed under G (Grommet) and come up with 107 knots GS exactly (and I am using a Papermate pencil with 0.5mm leads).

6)At this time I also noted a WCA of JUST over 9 deg to the right, so I settle on 9 degree WCA (not a water closet angle)

7) I now go about completing the problem by use of the formula above:

TC (True Course) -L or + R WCA (Wind Correction Angle) = TH (True Heading) -E or +W VAR (Magnetic Variation)=MH (Magnetic Heading) -E or +W DEV (Compass Deviation)= CH (Compass Heading

255 deg True + 9 deg (right WCA) = True Heading of 264 deg. I then take away the 5 degrees VAR (east is least) and end up with a MAGNETIC heading of 259 deg for the purpose of question 6. (I dont need to worry about compass dev or the resultant heading since the variables are not supplied nor computed for this question.

So my answers for Question 5 are as per my calculation: 259 deg magnetic and 107 knots GS.

Alas the answer quoted in the BT book is 268 magnetic and 105 knots. Now OK I can accept a tolerance of two knots Groundspeed but 9 degrees is way of course for the purposes of navigation.

Am I missing something here, its driving me nuts, and I had this issue on a couple of other questions as well, but I am getting correct answers off the E6B.

Any help greatly appreciated!

On the next question - Question 6 Page 3.8 - using the same mechanism and a 9 deg right WCA I get a MH of 172 deg and a GS of 115.

The answers however in the book are saying MH should be 187 deg mag and 110kt. That is 15 degrees magnetic off and 5 knots GS off.

Think I got it - my mistake was based on my workings in step 3. Still curious about the US vs Australian thing though, as it relates to flight computers and planning.

In terms of the expression "East is Least" (subtract) and "West is Best" (add)that is in reference to the original TRUE course. So the Magnetic course has already taken this into account.

For example, if the MAGNETIC Course was 300 deg for example, and the variation was 15 deg EAST, you would NOT subtract a FURTHER 15 degrees from 300 degrees thinking east is least, since this has ALREADY been subtracted (with reference to TRUE ALREADY being 315 deg). So if you get a magnetic course, you need to use reverse psychology and ADD East and SUBTRACT West to get your original SOURCE true heading.

FYI it also appears that the answer from Q10 is not there..

Brook

You will find that if you work the exercises using all directions as degrees true, i.e. wind direction as true and course [which we call flight planned track] as true, then you will get a heading as a true heading. Since directions on flight plans are usually written as magnetic, you would need to convert the answer to a magnetic heading by applying the local variation.

The other option is to convert everything to magnetic before you begin - wind as magnetic and flight planned track as magnetic. [This is the preferred method in most Australian flying schools]. You will then get a magnetic heading. It will be the same heading. A rule often used is 'any direction written on paper is always magnetic'. One good reason for this is that all directions on instrument approach charts and on ERC and VTC charts are always magnetic. Magnetic is the 'work-bench language' of the pilot'

So when you read the wind off the area forecast, you apply the local variation to make it magnetic before you write it down. When you measure the flight planned track [or course] off the map, you keep it in your head and apply the variation to make it magnetic before you write it down. When you get into the cockpit, you take the magnetic heading off the flight plan and apply the deviation from the compass deviation card [also mentally] to decide the compass heading to fly.

The ground speed in each case will be the same.

Thanks Bob - interesting. At the UK and US flight schools I have been involved with they both went off anything written was true, anything spoken was magnetic, and that was a big point they drummed into you.

The only issues I can see here (why I got confused at the Aussie Schools as well having done both) really comes from the use of the E6B and also the use of written material.

Interesting about Aussie instrument approach charts being WRITTEN in MAGNETIC. Now it makes sense!

So for you then as you interpret the E6B - would you just fill in any of the TC and TH below with Magnetic? (I wonder why this was not made a worldwide standard by ICAO or JAA?)

TC (True Course) -L or + R WCA (Wind Correction Angle) = TH (True Heading) -E or +W VAR (Magnetic Variation)=MH (Magnetic Heading) -E or +W DEV (Compass Deviation)= CH (Compass Heading

Australia is a member of ICAO, all ICAO instrument approach charts are written in magnetic. If you check the Jepps charts and maps, they are all in magnetic.

So Bob what do we do with the computer formula (below) - its written on the working area of the E6B, and typically expects you to pencil in the variables down the bottom of the computer. Do we simply change the True Course and True Heading to Magnetic? Will that work?

TC (True Course) -L or + R WCA (Wind Correction Angle) = TH (True Heading) -E or +W VAR (Magnetic Variation)=MH (Magnetic Heading) -E or +W DEV (Compass Deviation)= CH (Compass Heading)

I haven't yet done my instrument rating, but all of the sectionals /VNC's, WAC and VTC's are true not magnetic in both countries, so its interesting that when switching to instrument it also switches to Magnetic.

To me from your statements it seems when time is of the essence, magnetic is better, in terms of less time to recompute.

If you have a look at the FAA or King Schools Flight planning sheets, they both have spaces for TRUE course instead of magnetic, and then get you to apply the variation on this. Seems like a fairly pointless extra step if its easier just to do it all in Magnetic?

The CASA pre flight planning (VFR) sheets omit this True course area. I can scan a copy of each if it helps. It mainly just for the computer I am trying to make it consistent so if in the air I can feed in the variables as per the computers requirement.

Perhaps it would be better for you if you stick with working in true as the formula says. It really doesn't make any difference to the answer.

I have never heard of a VTC or ERC in any country that publishes tracks as true directions. See attached. All OMNI radials are magnetic and all GPS bearings are magnetic in every country. It seems you are asking for trouble if you publish tracks on the chart as true.

Thanks so much for that Bob, sorry I haven't been near a computer to reply sooner.

I have tried both the US calculations and the Australian Magnetic Calcs on my E6B and blow me down, the Aussie way is quicker and easier operationally.

Interesting. Intead of 7 Steps (USA) there are only 3 steps (Australia - BT) to achieve the same outcome. As soon as I'm near the scanner I will send over the VFR US stuff and dial of the computer by way of comparison.

I wonder why the Yanks Do convert to True all the time in the formula?

One thing I noticed - The yanks are bigger on Wind Correction Angle, Aussies on Drift which appears to be the same thing.

Hey, sorry to interrupt the conversation, but Bob, what program do you use to draw on the charts and make the diagrams for the book and stuff? If you don't mind me asking.