Calculating ETP for North Atlantic flights

[David Flynn]

Hi all,
I have an Aer Lingus (A330) Jeppesen North Atlantic plotting chart and on
the right hand side it has a graph:

Equal Time Point (ETP)

Enter the graph with continuing and returning wind components to determine
the equitime number (plus or minus)

Below the graph it says:

Returning Wind Component

Multiply this number by 1% of the total distance between the two points in
question. The product will be the number of miles the ETP is from midpoint.

If the product is positive (+), the ETP will be in the continuing direction.
If it is negative (-), the ETP will be in the returning direction.

I have a few questions about this. I though the ETP is the midpoint between
two airports say Shannon and Gander. And basically if the pilot has to
return the aircraft before this point, it would be quicker to go to Shannon.
If after this point it would be best to continue on to Gander. Would they
not be able to enter this midpoint into the FMS and let it do the
calculations of the ETA , etc which takes into affect the wind, etc?

Does anyone know how to work this ETP out using the graph that I am talking
about?
Iam a little unsure of how to go about filling in the graph and what data to use, etc.

I can describe it in more detail if you think you know what to do.

Thanks,
Best wishes,

David Flynn
Ireland

[tired]

David - ETP is NOT the midpoint between the 2 airfields, unless there's no wind, which ain't very likely. The ETP always moves into wind - if you're flying over the Atlantic, where there's almost always a westerly wind blowing at cruise height, the ETP will be closer to Gander than to Shannon. This is because your groundspeed is lower when you're flying into the wind and, conversely, higher when you're flying downwind.

And yes, the 330's FMS will do the calculations for you, I imagine the chart is a hangover from The Old Days when you had to do such things for yourself.

Hope this helps.

[This message has been edited by tired (edited 21 October 2000).]

[Checkboard]

From the Archive:

PNR usage (http://www.pprune.org/ubb/NonCGI/Archives/Archive-000002/HTML/20000905-3-000145.html)

I cover on and off track CPs about halfway down the page.

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Tech Log forum moderator

[USNA'65]

David,

Just signed on at PPRuNe, however, I spent 10+ years at Jepp. Have you received an answer to your request, and if not, can I assist?

[Icarus]

Aren't PNR's purely a fuel issue?

Anyway, this should help you!

http://www.aviationshop.com.au/avfacts/editorial/crit_point/default.asp

(You may have to get yourself a login ID and password first!).

[SentryIP]

Icarus,

Thanks! Excellent website.

Amin

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FIRST, FLY THE AIRPLANE!
SentryIP

[David Flynn]

Thanks to everyone who replied to my question over the last few months, I really appreciate everyone's help.

I have all the info I need.
Thanks again,

Best wishes,
David