latest point of safe diversion (LPSD)

[Pilotpeter]

Hi there,

I have been looking into LPSD calculation and at this time it is not making much sense to me. I've been trying to understand the explanation given on the site www.airsafaris.com.au/general_info/pnrcp.htm (http://www.airsafaris.com.au/general_info/pnrcp.htm) but it seems so complicated. What happened with keep it stupid simple.
Is there somebody out there that found a "simple" way of calculation this point for practical use.
I would like to know how to do it exactly, but i'm definatly more intrested in a way of doing it fast and simple even if the awnswer "close enough".
Thanks in advance.




P.S. Long live stupid simple.

[tmpffisch]

What you may be talking about is Point of No Return and Critical Point?

The point of no return is a position where you no longer have the flight fuel required to turn back to your departure airport.

Critical point is the halfway point between departure and arrival airports, with wind taken into factored into the equation.

PNR is 'safe endurance' multiplied by your GS home, divided by 2x TAS
CP is total distance multiplied by your GS home, divided by 2x TAS

[increasedescent]

We just call it the PSD where I'm from, something that is no longer part of the Australian ATPL syllabus. In answer to your question, no there is no simple (or exact) way of doing it by hand, in my opinion. The way I taught using the 727 was to 'guesstimate' and then iterate until the answer was within 10 nm of the previous. I have never been a fan of this method, especially when I assume today's FMC's can help out with calculations such as these.

ID

PS. PM me if you would like an explanation on how to actually do it, it's not fun.

[HarleyD]

I have used the method that you quoted and it is quite accurate, though very cumbersome, and the worst thing is that you MUST revise in flight for the reality check. I don't assume that the speed to the ALTN increases even if there is a so-called known tailwind, but am a little pessimistic as to GS for that leg.

A good GPS will help enormously and by switching between the two destinations this can provide some level of comfort to support the pre worked point (or not).

Another method I have used for long distance ferry is to depart from A for B when marginal but plan to track via C (off direct track). whilst enroute to C constantly update ETI/Fuel to B and when reasonable, though not always certain, begin to track for B and keep option to C available. this is a slightly different concept really but can be adapted as long as you are aware that B MUST be available for suitable landing on arrival there. C is then often still a better option as alt as it is still a bit closer usually because fop the slight dog leg. It allows departure, without commitment, to the desired destination and the ability to find the best altitude/speed/power setting that will allow safe completion (with reserves) to the desired destination.

And you were confused before I started!!

HD

[VH-XXX]

It SHOULD be included in the ATPL syllabus. I recall a large airliner (possibly a 747) some years ago heading for Perth past the Point of Safe Return even though Perth was closed due to fog. Luckily it cleared by the time they got there.

[Big Beres]

Forgive me guys if I'm not reading some of your relies correctly, but having sat both ATPL Flight planning (A) and (H), plus ATPL NAV in the last six months, there is most certainly questions on PSD's in the exams.
:{ :ugh: :confused:

BB

passed them all too first time round :ok:

[increasedescent]

Big Beres,

I too have completed nav and flight planning recently but was referring to calculating PSDs from scratch. I did not have to do this and as far as I know this has been the case for a while. Correct me if I'm wrong?

ID

[training wheels]

I did ATPL NAV about 3 years ago and I'm sure PSD's were in the exams then. If I remember correctly, the main difference between PSDs and PNR's were that PSD's were diversions to aerodromes that were off your planned track.

As for how to calculate it, I'd have to dig out my AFT notes which is in storage at the moment. It involved using your protractor and drawing on your ERC's factoring in your wind vector. Nothing difficult, infact, it was quite a fun exercise. I miss studying for my ATPL exams! :E

[MagicalLeoplurodon]

PSDs are still in the aeronautical knowledge syllabus for the ATPL.


4.6.4 Calculation of track and groundspeed
(a) review basic track and groundspeed calculations:
• plotted positions, IAS/TAS/GS, HDG/TRK
• determination of wind velocity
(track and groundspeed methods only)
• calculation of ETAs, EETs
(b) review ETP and PNR calculations;
(c) inflight diversion to fixed point:
• last PSD
• time and fuel required.

[AerocatS2A]

The way to do it for a multi-guess exam is to choose an answer and then work it out based on that answer. If it doesn't add up, choose another answer in an appropriate direction (either closer or further away depending on how the first answer worked out.)

That might sound like "cheating" or taking the easy way out, but when you're flying with an FMS or GPS you can basically do the same thing except instead of choosing from multi-guess answers, you just choose from enroute waypoints (as described by DirectAnywhere.

BTW, I did ATPL nav a few years back and off track PNRs were part of the exam (I had the joy of trying to work one out with a track that went across two charts, printed on opposite sides of the same piece of paper!)

[increasedescent]

PSDs are still in the aeronautical knowledge syllabus for the ATPL.Yes, under Navigation, but not under Flight Planning;

5.4 PRACTICAL FLIGHT PLANNING AND FLIGHT MONITORING
Complete a practical flight planning exercise using specified initial conditions and Operations Manual data. Other conditions may be inserted or varied enroute for test purposes. The exercise is intended as a consolidated test of a candidate's
ability to apply flight planning, performance and navigational principles, and will include:

(i) calculation of CP, ETP and PNR:
• normal
• engine-out
• depressurised.

No mention of PSD. Which is why, combined with the fact I did not face a full PSD question in my exam, nor have I heard of any others, that I have drawn the conclusion that calculating a PSD from scratch is no longer required. I understand there are numerous questions in nav. requiring fuel and time calculations but none (that I have heard or seen) requiring a full PSD to be calculated. If anyone has recently, please let me know, I will consider myself lucky for not getting one!

ID

[MagicalLeoplurodon]

PSDs are certainly in the syllabus and I believe it is intended that you know how to do them -

for example:

Flying MMB - AD
now at position X
How far can you continue on to AD and still make it to BHI

Pretty sure the Higgins course is still teaching it?

Needless to say some put emphasis on using the multi-choice answers and working from one of them to get the actual answer (is that where 'not having to know how to do them from scratch' comes from?).

[Pilotpeter]

Hey guys

Thanks for the replies on this thread, all of you're inputs made me learn a lot more about the lpsd.

The main reason for me looking into it was that i just finished my JAA atpl's and it wasn't part of the syllabus. But as I am doing know my australian IR it came up in a questionaire the school gave me. To prep me for the theory part of the ir test.
I don't expect to be questionned about this but it tickled my curiousity and if they do I don't want to stand there doing the eeeeeeuuuuuhhmm routine and know something about it.

Conclusion: (and correct me if I'm wrong) Too hard to do as part of a pre flight planning, i'll spend the 20min it would take examining the weather. And then let the gps do the hard work calculating it for me in flight.
The birds that would really need would have a fmc do it for them.