Tech Log The very best in practical technical discussion on the web

PNR usage

Old 12th Jan 1999, 16:17
  #1 (permalink)  
Jetone
Guest
 
Posts: n/a
PNR usage

Does anyone know the circumstances under which one uses PNR and whether it can be used for an engine out calculation for a four engined aeroplane? It has been some time since I did my ATPL's. Does anyone use PNR under normal long haul operations? Any info would be a help.
 
Old 13th Jan 1999, 16:49
  #2 (permalink)  
PODKNOCKER
Guest
 
Posts: n/a
Yes PNR is included on our B747-400 flightplans on the Atlantic all the time, using 3 engines back.
 
Old 14th Jan 1999, 01:42
  #3 (permalink)  
tired
Guest
 
Posts: n/a
Yes, we use it on the 340 as well
 
Old 14th Jan 1999, 02:45
  #4 (permalink)  
Airtours Inmate
Guest
 
Posts: n/a
Do you have to calculate the PNR and/or Crit Point yourselves or is it included for you as part of the pre-flight package produced by ops ?

Cheers
 
Old 14th Jan 1999, 03:03
  #5 (permalink)  
mustafagander
Guest
 
Posts: n/a
Jetone,
A PNR is needed in most long range ops. You've gotta know where you can't go as well as where you can. Mostly we need to know ETP for the engine failure case and the depress case.
Except for areas with airports all over the place, PNR and ETP's are necessary and calculated by the flight planning system for all long haul ops in Charlie Q.
PS We usually check it ourselves too.
 
Old 14th Jan 1999, 07:56
  #6 (permalink)  
XL5
Guest
 
Posts: n/a
Airtours.I suspect that you ask your question because the slog of PNR/CP determination is still part of the ATPL writtens.
Rest assured,the flight ops computer system looks after the mumbo-jumbo.There's a lot of information on the standard flight release,more than needed really, but the figures for fuel and time are usually in close agreement with those experienced enroute.
 
Old 15th Jan 1999, 01:57
  #7 (permalink)  
 
Join Date: Jun 2001
Location: Sydney
Posts: 106
Eagle flight plans can be produced to provide any of this information. Its a good idea to update PNR and ETP en-route as 1) winds and fuel on board will always be slighty different and 2) it gives you somthing to do besides geting the volmet. The type of PNR or ETP that you calculate (E/O, Depress., or All Eng) is up to you. My view is that normal cruise CPs are usefull for medical emergencies, cargo fires and other similar contingencies where diversion to the nearest funkhole is in order. Depressurised PNRs are used for in-flight diversion if the destination airport is unavailable for any reason. This may be WX but could also be for mechanical problems where the company wants you to land at a particular base rather than proceed to destination. In short, use the CP or PNR that fits the divert senario under consideration

[This message has been edited by ANFO (edited 14 January 1999).]
ANFO is offline  
Old 15th Jan 1999, 05:57
  #8 (permalink)  
 
Join Date: Aug 1998
Location: Ex-pat Aussie in the UK
Posts: 4,531
OK, how about comparing some methods for calculating inflight Critical Points (CPs)/Points of No Return (PNRs) (for on-track work) and Equi-Time Points (ETPs) and Last Points of Safe Diversion (LPSDs) (for off-track work) that are reasonably cockpit friendly?

ETP:

Take your map (that piece of paper that hides at the bottom of your nav bag, under last month's Playboy ) and fold it so that the two airports you are considering are placed directly on top of each other. Crease the fold line between the two airports and open up the map.

The crease line is the perpendicular bisector between the two airports. (I made that term up , it means that it is half-way between the airports, and at right angles to them)

Any point on this line forms an isosceles triangle with the two airports, (An isosceles triangle is any triangle having two equal sides.) and is a nil wind ETP. Of course the point we are interested in is the place where the crease line crosses our track. This all takes about two seconds to do.

How to adjust for wind? The fastest way I know is to use the GPS/FMS in the cockpit. Set up a point on track at the nil wind ETP, then eye ball the wind vector. Consider the effect that the wind will have flying to each airport (i.e. if it is all cross-wind to ariport 'A' but all head wind to airport 'B', then you will have to slide the ETP along track so as to make the flight to 'B' shorter than that to 'A') I can usually find the actual ETP in about 60 seconds this way. You can even include this point in the GPS flight plan, and have the GPS tell you when you have passed it.

Don't have a GPS/FMS? (Hold on for the maths bit ) find the nil-wind ETP as above, calculate the time to either airport, nil-wind. Multiply that time by the wind (ie time of an hour and a half, wind of 30 knots = 45 nm) Now draw the adjusted wind vector so that the head of the vector is where the crease line crosses the half way point between the two airports under consideration.

Project the vector onto the line between the two ariports. (ouch! what does that mean?) It means take the cosine of the angle between the wind vector and the track between the two airports and multiply it by the length of the vector. (phew!) Not following - forget it then, you don't need to do this and you really need to be comfortable with trigonometry for this method. Now move the "perpendicular bisector" point along the line between the two airports the same distance as the projection, and draw a new "crease" up to your track - this is a pretty good approximation, within a couple of miles, of the actual ETP. (that's right, after all THAT it's only an approximation, which is why I said to "forget it" before )

To adjust further you will need to go into trial and error adjustments as per the GPS/FMS, and that is actually just about as fast if you didn't (want to) follow the trig stuff above. I can usually get an actual ETP in about 2 minutes (by which time the aircraft has travelled further than the adjustment! )

So what's the big deal about ETPs? Well, with the map thingy (takes about two seconds remember) you get a fast approximation, and sometimes (vary rarely) you need to work fast. Also if you have planned enough fuel to your destination then the LPSD is always PAST the ETP, if one of the airports being considered for the ETP is your destination, of course. So you also get an idea of where your LPSD is, or at least how much time you have to calculate it.

LPSD:

Calculate the fuel available for the LPSD. (i.e. Fuel on board minus fixed reserve minus holding minus variable reserve (1.1) minus approach allowance)

Calculate the fuel required to fly all the way to the destination (in the configuration you are considering) then to the diversion you are considering.

Now, Fuel available for LPSD fuel required = dist to LPSD distance to destination. (Well... almost! )

So divide fuel available by the fuel required, then multiply that by the distance to your destination. This will give you an approximate (within 5%) distance to the LPSD.

To correct it plot this position, calculate the actual fuel to LPSD, then to diversion and compare it to the fuel available. If it is a little high (how many miles will this XS fuel require?), move the LPSD towards you enough to reduce the total track miles by an amount that would save the XS fuel, and check (or vice vesa). I can find the actual LPSD in about 90 seconds this way. Including this point in the GPS plan will have the GPS tell you when you have passed it.

Any other suggestions???

[This message has been edited by Checkboard (edited 15 January 1999).]
Checkboard is online now  
Old 16th Jan 1999, 02:06
  #9 (permalink)  
 
Join Date: Aug 1998
Location: Ex-pat Aussie in the UK
Posts: 4,531
While I'm at it...

for you piston guys, in the Australian regs there used to be a requirement for twin aircraft to ensure that they have enough fuel to fly (on two engines) to the single engine CP and then fly one engine out to an airport.
I don't know off the top of my head if this requirement survived the "just don't run out of fuel - OK?" changes where the CAA decided to get fuel reserves etc included in Company Ops manuals (of which maybe 10% have been ammended after 5 odd years, I bet...) however as most pilots learnt CPs at CPL stage, and that was, pehaps, two - three years before they really started flying twins, I bet that hardly anybody does this.

Of course the whole situation is not helped by the manufacturer's manuals, very few of which (especially Piper's) give any numbers for single engine cruise, but that's another whinge...

So, time for a "Rule of Thumb"

When a piston twin loses an engine, it has to slow form its normal cruise speed (with lots of parasite drag) to close to the long range speed. You will find that the aircraft is flying more efficiently on one motor at the single engine cruise speed, than on two at normal cruise! (but not as efficiently as on two at long range cruise, due to the added drag of the engine out thing.)

So the aircraft will fly furthur (through the air) one one engine than on two! Doesn't work for turbines, as they are forced to operate at a (inefficient) lower altitude.

So, the rule of thumb? If the headwind is less than 25% of the single engine cruise speed, planning normal ops fuel will also cover the engine out case.

So now you can say to the CASA guys when they jump out from behind the fuel bowser - yeah, I planned for that, and proceded to baffle them with the above!
Checkboard is online now  
Old 20th Jan 1999, 09:35
  #10 (permalink)  
Jetone
Guest
 
Posts: n/a
Thanks to all for your response the contents of which were noted. A special thanks to Checkboard for his technique which I used recently much to the amazement of my colleage. But it works and thats all that matters. Yes ETP's are included on the flightplan but not for two intermediate points for those of you who were wondering (Airtours inmate).
Happy Landings
Jetone
 
Old 20th Jan 1999, 10:08
  #11 (permalink)  
 
Join Date: Aug 1998
Location: Ex-pat Aussie in the UK
Posts: 4,531
Thanks - it's nice to know somebody read it!
Checkboard is online now  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.