Point of Last Safe Diversion to a Moving Target

[kalavo]

I know how to work out a PNR and PLSD, but does anyone know how to calculate a Point of Last Safe Diversion to a Moving Target (e.g. aircraft carrier).

Would be very interested to see the solution if anyone has an example

[Lefthanded_Rock_Thrower]

The standard PNR calculation will do it, you just need to adjust the GS to counteract the GS os the aircraft carrier ( not very practicle as the carrier might be tracking an oblique heading ).

The easiest way is to PLOT it is using a PLE chart, once you set up the PLE chart, you pretty much plot FOB V's NM to base, once your plot hits the PLE line go home, also really usefull for airwork such as prawn spotting or coastwatch.

Shoot me a PM and i'll send you a PLE chart.


Cheers

[Fred Gassit]

There is a workbook that Jeppesen puts out for their flight computer (whizz wheel), this is an A4 size book, not the little one that comes with the wheel.
Full title is CR Computer Manual/Workbook BW-2

Get a copy of that from a pilot supply shop or online somewhere, it has fully worked solutions for PSD/PNRs to moving targets.

[mustafagander]

I'm not sure that I'd get too excited about how far a carrier might move. Even at 30 kts it won't go far enough to be worth allowing for.

Re read the theory of PSD etc. and see how limited the accuracy really is. If you are bored, use PA31-350 numbers to calculate a flight SYD - LHI and find PSD, PNR etc. on PMQ in nil wind, 50kt westerly and 50kt easterly.

[Sunfish]

The question is oxymoronic. How could a diversion, presumably for a carrier landing, be safe?

[WannaBeBiggles]

Sunfish, I think Kalavo means a PNR from a land base to an aircraft carrier.

The carrier just becomes good ol' 'Point B' in your PNR calculation.

[FRQ Charlie Bravo]

Wait a minute; what about taking into account the movement of land-based aerodromes too... do to plate tectonics of course?

OK sorry to be a tosser. I would think that the relatively slow speed (very very very rarely more than 35 knots if memory serves from my time on them and then that was only to go back to the top of the box to steam back into the wind for a handy 12 knot headwind across the deck) makes this a bit of a moot point. But while we're at it, if you really were in the **** and needed to 'divert' to the ship they could of course steam towards you or even send a tanker out to top up so that you could make it wherever you needed to go.

Interesting question...

Just head back to them and request the choppers to meet you. Once you're gliding at 3000 fpm eject and get ready to give some answers trying your best not to drip sea water on the skippers deck:ok:


FRQ CB

[kalavo]

Thanks for all the responses. I find the ones saying "its only 30kts" interesting, when I'm sure the same people would definitely account for a 30kt wind in the CASA exam ;)

The hint of "Radius of action" mentioned by someone was a good one.

For those interested but not wanting to mess around on the CR2, this website gives a great visual of what's going on...

http://www.luizmonteiro.com/RA_MovBase.aspx

[Bozzo]

Not such a silly question if you substitute the aircraft carrier scenario for say a boat in distress (or search & rescue) with a known position and a course and speed(or known/predicted drift rate).

I would work this out by taking known position extrapolating this with course and speed (eg. 30kts @ 2hours + 60nm) to calculate position at ETA and apply pnr to this position. Of course the ETA would need to be adjusted according to targets course relative to you.

BTW some Universal FMCs have a drifting target function which will do this for you.

Even two hours drift or movement at say 15kts equates to 30nm and in low vis at low level this can make a difference.

[mustafagander]

Kalavo,
Just work it out for yourself from first principles and you will see what we are getting at.
When you recall that an approved CASA method of determining PSD for exam purposes was a piece of string cut to the scale length for safe endurance and 2 pins to stick in the appropriate airfields, I expect you will see what I mean.

[kalavo]

Kalavo,
Just work it out for yourself from first principles and you will see what we are getting at.
When you recall that an approved CASA method of determining PSD for exam purposes was a piece of string cut to the scale length for safe endurance and 2 pins to stick in the appropriate airfields, I expect you will see what I mean.

Have since done so, ta. Trying to get back in to the books (knocked off all the CASA exams long ago, but no where near current) that was one this was missing from my notes and had me stumped late one night. Bit more sleep and it's a lot simpler than I first thought.