Hi All,

I'm just about to sit my CPL Nav exam.
My question is in regards to finding Heading and Ground speed from known winds and track. Does anyone know whether or not the CASA exams expect you to use TAS or ETAS when calculating your Ground speed?
Some practise exams I have done have answers relating to either or.

Any help would be greatly appreciated!

Hi Mick,

If you are using the CR3 type of flight computer from Jeppesen you will be working with the effective TAS if you are correcting for more than about 10 degrees of drift. See this forum thread for more info:

www.bobtait.com.au/forum/bak-ppl/3218-wo...nd-ground-speed#3233

If you are using the E6B type of flight computer, you work with TAS.

The reason you have to use effective TAS with the CR3 is because it uses the wind components to deduce a solution for HDG and GS whereas the E6B uses vector addition to determine HDG and GS directly. The CR3 approach needs much less space (and therefore a smaller design) but with large amounts of drift, for reasons of geometry, the resulting groundspeed can be off by several knots. You need to adjust the TAS and use an effective TAS for drift corrections of more than about 10^o.

Cheers,

Rich

P.S. the child in your avatar is the spitting image of one of my kids. Wow, that was a double take! Good looking aren't they though - must take after their fathers

Hi Rich,

Thanks for your reply.
Your a massive time saver!
I use the CR-3, and some times the Electronic E6b on my iPhone.
It makes a lot more sense now, especially when comparing the two.
Your links are very helpful, I'll have to read more of them.

Spitting image hey! Their both got good geans mate.