Off Track PNRs

[m-dot]

Can anyone PM/provide any notes/guidance/non complex method for solving off track PNR situations please.

Cheers Big Ears

[Chimbu chuckles]

Point of Safe Diversion

Safe end avail x ETI->Desto/ETI->desto + ETI Desto->Alternate.

Can't draw diagrams here but draw on a pice of paper a Point A.

Point B (Desto) draw at 12 o'clock a suitable distance up the page. Point C (Altn), draw a line from B to a Pont C at 4 o'clock and a suitable distance down and across.

Example;

Safe Endurance available is 60 minutes.

ETI A->B is 40 minutes.

ETI B->C is 30 minutes.

X = the distance (in minutes) you can travel from A->B and still make C with reserves intact.

X= 60x40/40+30

X=2400/70

X= 34.2857:} minutes from A.

It's been many years since I used the above but it's easily proven by then calculating cruise fuel flows x time intervals from A->X->C to ensure yourself that it works....obviously you want to arrive at C with reserves intact and enough fuel to carry out an approach and landing, or hold first then approach and land, if the weather is such, so be carefull with calculating safe endurance...this is where you'd likely make a mistake that invalidates the formula.

It's merely a ratio type calculation.

Hope that helps

Mind you the type of simple, efficient calculation above is not gauranteed to give the right answer on a CASA flight planning exam...they would require 40 minutes of number crunching to come up with their 'correct' answer...this one would work in the real world though...and you wouldn't be past the PNR by the time you'd worked out where it was:ugh: :uhoh:

Editted for the playfull smiley I forgot to add after the 4 decimal places...and yes Woomera you'd hope those days were over...but are they?:ok:

[Woomera]

Chuckles hopefully we are beyond the days when you had to work out your fuel to six decimal places to get it to "fall" into the "right" box:rolleyes: and then when you point out and demontrate that by any rational method of calculation the "correct" answer is in fact wrong, you no longer get the "if I tell you that I'll have to kill you" routine. :}

[m-dot]

Chimbu

Moochus Appreciatum (my version of a latin thankyou!)

Cheers

[The Messiah]

You reeeaaaally want to talk to Len Sales.

[swh]

Chimbu,

Much easier just to put the the aerodromes into the FMC/FMGC and let the ETP come up on the screen infront of you.

:=

[Chimbu chuckles]

Yeah....I did say it's been years since I used it:ok:

[QSK?]

Wasn't this same subject discussed on a PPrune thread a couple of months ago, where some kind gentleman (from the RAAF I think) eloquently answered this problem with diagrams??

[Woomera]

m-dot

Try a PPRuNe search and put "off track PNR" in the field search all forums and you will find a treasure trove of info.

Including one from our esteemed Compressor Stall:ok:

Go to Tech Log Checkboard the mod there is another home grown product.:D ask there and be prepared for a deluge of info.

QSK you're right but I can't find it do you want to have a go.:uhoh:

[QSK?]

Woomera

Sorry the link I was thinking of referred to Critical Point diagrams not PNR.

The link for info:http://www.pprune.org/forums/showthread.php?s=&threadid=142038&highlight=Critical+Point (http://http://www.pprune.org/forums/showthread.php?s=&threadid=142038&highlight=Critical+Point)

Regards QSK?