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Hello, I was wondering what the difference is between the critical point and the equal time point. I realize that when using CRP I end up with some extra fuel called ETP fuel or something like that, I did a little reading and found that basically the CRP is a point in which you choose to continue or turn around but isn't the ETP for that same purpose? How would I know whether to use CRP or ETP in my planning.

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Others will have to provide the more detailed analysis. CRP comes when you don't pair ETOPS alternates or have an odd number of them. As i understand it, these are "unbalanced ETOPS" solutions, but someone else would have to explain balanced versus unbalanced. They represent the point at which the maximum amount of fuel is necessary to reach your diversion airport. After reaching this point, you will go to the next diversion airport instead of the last one. Conceptually that seems very very similar to ETP, just with fuel instead of time. That's also where someone else will need to clarify the details here, as they seem very similar to me.

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Asked and answered - use the search function.

Where? If I use this forums search function in the PFPX forum searching for "CRP", zero results are returned. I am aware of a single thread regarding this because I started it. This is where I learned the information that you get CRPs instead of ETPs if the airports aren't paired. The closest answer to the questions about CRP vs ETP was that they are "basically the same". Basically doesn't mean they are the same and it's the small nuanced difference that I am interested in.

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Let me clarify...this excerpt comes from PPRUNE forum...

Our flight planning depatment run three scenarios from the ETP and the one requiring the most fuel is applied. The 3 scenarios are;
1/Engine failure and descent to appropriate height.
2/ Engine failure and depressurization with descent to 10,000ft
3/ Depressurization, two engines, descent to 10,000ft

Most of the time the 2eng depressurized is the most critical. The flight plan fuel is 'built up' to ensure that at the ETP there is enough fuel to cover the worst of these three scenarios.

The CRP is the point at which, based on the most critical of the three above scenarios at the ETP. The CRP in terms of TIME and the ETP should be the same. Remember, you will have multiple CRP (ETPs) based on the number of diversion airports that are included in the route.

This is the entire thread.

http://www.pprune.org/archive/index.php/t-361923.html

Hopefully this helps...I googled "Critical Fuel Point vs. Equal Time Point" on Google to get this; since I don't deal on a daily basis with ETOPS, I had to do some research.

Kind regards,
Dave Lamb

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Depending on the position of your ETP Airports, CRP is not always the ETP in ETOPS flights.

It's a little bit difficult to explain without drawing a picture.

1) imagine 3 Etops airports (2 etps), 1 airport before the eep, 1 abeam your route, 1 after the exp. In most cases the second etp is the crp, because after the second etp, you are flying closer to the last airport and you will need less fuel to perform etops diversion.

2) imagine that you don't select the third airport, only one etp between first and second airport. The second airport range ring covers your etops area.

In this case the CRP is the EXP. Because if you have a failure between the ETP and the EXP you have to return to the second airport. Passing abeam the second airport and until the EXP, you are flying away. If you have to turn back and divert you will need more fuel, and the fuel on board is decreasing.

Stéphane LI-THIAO-TE

Envoyé de mon iPad à l'aide de Tapatalk HD

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So, to make a long story short, when two airports are "paired", they become ETP airports, when they remain unpaired they are CRP, which is more "unbalanced". From what I understand, ETP is based on time, CRP is based on fuel. But what are the rules for "pairing" ETOPS airports? My assumption was that they need to be close to each other to provide redundancy in case one of the 2 drops below weather minima or closes for another reason. However in the Program Overview 2 video, where ETOPS is demonstrated on a north atlantic crossing, BIKF is paired with CYQX.

My question is: what are the conditions that allow BIKF and CYQX to be paired? Why shouldn't they be seperate? And what exactly is meant with a "more balanced solution" in case of paired ETOPS airports?

Thanks in advance!

Mark Jansen

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Your post explains a lot, thanks for that, but I still don't fully understand the difference between CRP and ETP. You wrote that "in cases of the unbalanced ETOPS, the critical fuel scenario is protected from the furthest point (ETOPS Entry or Exit) to the Chosen ETOPS Enroute Alternate airport." What is meant exactly by "a fuel scenario being protected by the furthest point"? And how is an ETP-scenario better (more balanced) than CRP?

I'm sorry that I don't get it yet. I'm definately not stupid but the manual is brief and there hasn't been much information on how to use this. More information would be appreciated. Thanks in advance for your efforts!

Mark Jansen

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Well, in ETOPS you gotta protect the critical fuel scenario. For large areas (think transatlantic) an airport pair does that, in that it creates a point of no return. For small areas, where one airport will cover the entire area, if the flight planning system permits, you can use unbalanced etops with a CRP - a Critical Point. See the image, and notice the very small ETOPS area along the right side of the image. The rings are the 435 adequate airport circle - any flight of any duration outside the 60 minute arc, you have to play the whole etops game.

With a single airport, there is no equal time point. But, you still gotta protect the critical fuel scenario fuel. So, the system protects from the furthest known point - either the etops entry point or the exit point, from the chosen etops enroute alternate airport. My chosen airport is RJCM, so the system will calculate both the etops critical fuel required from both the entry and exit point, and which ever is higher, it will protect that fuel. So, lets say I need 65.0K in etops critical fuel required from the entry point, and 62K from the exit point. The system will ensure that I will have at least 65K aboard at the etops entry point, to insure the etops critical fuel required is protected.

In a large area - think transatlantic, you need a pair of airports. In small areas, like in the picture where one airport can cover the entire etops area of operation, a CRP will suffice.

post-92299-0-62642300-1378553610_thumb.j

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Thanks that really explains a lot more, one question, when you get the results of the 3 etops scenarios, do you pick one and use it no matter what happens or you can use all 3 depending on what failure you have during flight?

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Yes but if anything happens enroute, say you lose an engine, do you use the 1EO ETP point, and if you lose pressurization do you use the 2ENG depressurization? Or do you select the ETP point that requires the most fuel and use that point only, for any failure you have?

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The required diverting fuel is calculated for each scenario, and the highest must be on board before leaving the block at the departure airport.

Stéphane LI-THIAO-TE

Envoyé de mon iPad à l'aide de Tapatalk HD

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Okay so the higest must be on board, does this mean that you are allowed to use all 3 scenarios in case of a diversion/emergency. In other words, in post #6 above by Dave Lamb, 3 scenarios are calculated and presented. When in flight and you have to divert are you allowed to use and apply only 1 of 3 scenarios no matter what type of emergency you experience in flight, so for example you choose the 1 engine out depressurization scenario and use that ETP, what if you experience 1 engine out and still have pressurization OR you have depressurization but still fly on 2 engines? Or can you switch the ETP/scenario from 1 engine out depressurization to the 2 engine operative depressurization?

I hope i explained my question well enough.

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When you have a no crap real world issue requiring a divert, the crew isnt going to screw around and try and determine which airport to go to; they're going to go. The crew maintains the awareness of where they are on the flight plan, and their location relative to the critical point, whether CRP or ETP. While yes, the critical fuel requireds are calculated simultaneously and are independent of each other, the airports in each of the three scenarios are the same.

USUALLY, but not always, the points are all fairly close to each other. The crew will display on their navdisplay the one requiring the most fuel at the ETP/CRP.

Here in the picture, there's 7 miles between each of the points (my Cathay Pacific format), in any event requiring a divert, its the Captain's call as where to go; not mine, and not the flight plans.

post-92299-0-04795400-1378583510_thumb.j

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