Hi all,
I’ve been working through PNR and ETP questions and wanted to check if using ETAS is a must. I have an ASA E6B flight computer, but since ETAS isn’t built into it like the CR3, and calculators with cosine functions aren’t allowed in the exam, I’m wondering how to approach these calculations manually. Did anyone have 3 or 4 point questions with high crosswind components, Any tips would be appreciated!

Thanks!

First, if you are using an E6B (Dalton), ETAS is absolutely irrelevant as the Dalton solves the wind triangle purely graphically. This process makes no use of ETAS. While you, physically, can figure out ETAS values on the Dalton, it is only a cute trick of no interest or value to the Dalton's solution. Just run the usual Dalton technique and all will be well.

CASA is not going to ask you to play with ETAS in the exam as ETAS only has practical meaning for the CR and the exam is not restricted to the CR, ergo, CASA would have a real bunfight on their hands were they to ask ETAS questions.

The only thing to keep in mind for the CR is that the nonsense about using ETAS if the drift is greater than 10 degrees is just that ... pure nonsense and dates back to some old ideas which make no sense now and didn't back then, either. The correct, trigonometric, solution for the wind triangle using the CR ALWAYS involves ETAS (unless drift is zero) so ALWAYS run the ETAS calculation, regardless of the drift value. Keep in mind that you have to set up the sine calculation to figure out the drift value and that sets you up for the cosine calculation to figure ETAS so why on earth would you NOT spend 1-2 seconds looking up the ETAS value. Also, keep in mind that CASA doesn't use the 10 degree nonsense so, if you do, then you are introducing an unnecessary error which CASA doesn't recognise.

You mention figuring cosine and sine values. One of the useful features of the CR solution is that the calculator includes both sine and cosine scales which are there for you to look up and/or use as you see fit.

Hi John,

Your detailed reply is greatly appreciated—it has clarified my question well. I apologise if this question has been asked a million times. Just to confirm, when you refer to the E6B "(Dalton)," are you specifically referring to the versions with the sliding grid? The one I am using is: www.flightstore.com.au/asa-metal-e6b-flight-computer

Cheers

Will,

That's a Dalton.

Originally designed (in several forms) by Philip Dalton in the US in the mid-30s. After the patents expired, every man and his dog produced clones.

The CR concept dates back to the DR2 designed by Siegfried Knemeyer in Germany, again, in the mid-30s. Post war, it fell into disfavour (why, I don't know). Subsequently, Ray Lahr (US) developed the idea (some good bits, some not so good), sold the rights to Jeppesen and, after the patents expired, again, every many and his dog produced clones.

The only real confusing bit is when some clone manufacturers entitle their CRs in a fashion such as an "E6B Circular" which is pretty silly as E-6B was the original USAAC designation for the Dalton.