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# JAA ATP - GNAV - Dead Reckoning

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# JAA ATP - GNAV - Dead Reckoning

29th Oct 2011, 22:44

Join Date: Jan 2006
Location: Europe
Posts: 403
JAA ATP - GNAV - Dead Reckoning

I noticed that using the CR-3/5 for solving the following type of questions (wind triangles - Dead Reckoning) is not really that accurate, since the given answers are somewhat close together. What's the best way to find the correct answer?

Example:
TAS = 170 kt
HDG (T) = 100°
W/V = 350/30 kt
Track (T) and GS?

1. 109 - 182 kt (correct answer)
2. 110 - 180 k
3. 103 - 178 kt
4. 091 - 183 kt

Thank you!
30th Oct 2011, 08:31

Join Date: Feb 2002
Location: Sunny Solihull
Age: 65
Posts: 216
Have you actually done this problem with a small pencil dot and the correct method? Using my 35 year old CRP-5 I have no problem in getting the right answer, mind you that's with 40 years of experience!

Remember the question is asking TK & GS not HDG & GS.

1. Put in wind DOWN.
2. TAS of 170 on centre dot (grommet).
3. Turn to put heading on 100 at the top.
4. Pencil dot should now be on 8/9 right drift line at about 183 kts.

109 at 182 no question.

Check your CRP-5 is not too slack and the grommet remains on the centre line at all times when moving up and down. If not it could explain some of your problems.

Also remember wind blows from heading to track answer 4 can't possibly be right before you even start.

You could of course draw a vector diagram to scale, but you won't have time in an exam for that. Get used to using your CRP-5 accurately then quickly.
30th Oct 2011, 17:10

Join Date: Apr 2009
Location: down south
Age: 75
Posts: 13,227
If you consult the navigation tutor at your JAA approved service provider I am sure you will receive the correct method.

30th Oct 2011, 17:18

Join Date: Jan 2006
Location: Europe
Posts: 403
Thanks Richard! Well the problem is not how to work it out with the CR3, but that the given multiple choice answers are sometimes so close together that one can easily be mistaken. So I was wondering if there was a mathematical way/formula to get this type of question(s) figured out?

@ Lightning Mate:
actually I'm doing the conversion from FAA to JAA and I'm exempt from ground school, which is on one hand an advantage (saves money) but on the other it can be a disadvantage (sometimes).

Last edited by Transsonic2000; 30th Oct 2011 at 17:38.
1st Nov 2011, 00:11

Join Date: Jun 2007
Location: Scotland
Posts: 15
Rough Formula

1st Nov 2011, 10:40

Join Date: Oct 2000
Location: Bristol
Posts: 461
You can solve a triangle if you have the length of two sides and one angle. This is O level maths' Label the angles A, B and C and the sides oposite to them a, b and c.

The formula is a/SinA = b/SinB = c/SinC

You have two sides, TAS 170 and Wind 30 and one angle - between hdg and wind direction

Good luck

Dick

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