Author Topic: Redispatching flights  (Read 1089 times)

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Offline Adrian Chitan

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Redispatching flights
« on: March 30, 2016, 01:12:53 PM »
Hi guys,

yet another post from me. I found a little free time so I checked some of the things I put in my "to-do" queue and thought why not share it with you.

In this post I am going to talk about the redispatching of flights, which is a method to save money on fuel employed by airlines all over the world. The post will not delve too much into the theory behind the concept but will focus more on an example.

Fuel policies

As you may know, there are a multitude of fuel policies around the world that impose fuel quotas for every flight that adheres to that policy. For example, European airlines obey the EU-OPS policy, while US airlines obey one of their fuel policies (e.g. US Flag Jet or US Flag Piston or US B343, etc.). Internationally, airlines could obey the general ICAO policy. One thing to note is that even though an airline could be flying all over the world, it will always obey it's home fuel policy because that is what the airline adhered to, so you should never change your fuel policy unless you change the airline and its location.

These policies are regulations about how much fuel should be taken on board for every flight. I won't go into the details of what EU-OPS requirements are because I guess that can be found on the internet quite easily and this is not a judicial post :). The thing to keep from this small introduction into fuel policies is that policies use percents to impose fuel quotas so long range flights will have to carry much more fuel than short flights.

The solution

Airlines and aviation administrations found a solution to pull down the fuel quotas imposed by the fuel policies, while still obeying them. This can be achieved by redispatching.

Dispatching means that a dispatch authority (all airlines have one to create and publish their flight plans) creates and publishes a flight plan for a certain flight that will take place. The fuel planning obeys the fuel policy of the airline.

Redispatching means that while the plane is still in flight following the initial dispatch, a new flight plan is created and published for the reminder of the flight still obeying the fuel policy. The idea is that if you divide a long flight into smaller flights, you will get a smaller initial amount of fuel required and so the airline buys less fuel for the flight and still obeys the fuel policy. Of course, you cannot redispatch a flight 10 times to get even smaller ammounts of fuel because there are rules for redispatching too (i.e. only one redispatch per flight because of the workload involved).

An example

To put more light on the subject, I will discuss an example here. Because this is not easy stuff and I am not an expert yet, I used PFPX to create the example as accurate as possible to real life. Nevertheless, this can be done by hand if you read the fuel policy and know the fuel burning customs of the plane.

The flight I have chosen takes us from San Francisco to Amsterdam (only long flights take advantage of the redispatching rule) under EU-OPS rules. Weather is ON, so this is an actual example of a flight that would departure around 12:15 UTC from San Francisco today 30th of March 2016. The flight is 4749 nm on the great circle (shortest distance) and PFPX gave me a flight plan of 4820 nm, with 4920 nm if we take the wind into account (the speed of the average wind is computed as a distance loss/gain). I also have to add that the plane is the B777-200LR with LRC as the cruise profile and we have 300 adults on-board with 10 tones of additional cargo in the bay. Of course, because this is a over the Atlantic flight, the flight plan obeys the E-TOPS 180 one engine operation policy.


The no-redispatch computation is pretty straight forward and the value of the cold and dark fuel quantity required by EU-OPS policy is: 104'058 kgs of fuel. This means that the airline is obliged to buy 33'259 euros worth of fuel for the flight as you can see in the image bellow:


Now we setup the redispatch. This has a special tab in PFPX, just like E-TOPS. The rule is that redispatching is done on the last part of the flight (the last 1/3rd part of it). For redispatching you need a fix from your flight plan (redispatch fix) and an airport that is around that fix (redispatch airport). The translation of the redispatching is that your airplane will actually turn to land at the redispatch airport after passing the redispatching fix and will then continue its old flight plan to the final destination. But because there is no landing and take-off, you don't need the fuel for it but your new flight plan will start you in the air at the cruise level (no climb) flying for your final destination.

For this flight I have chosen AGORI as the redispatch fix that comes right after the Atlantic part of the journey. The closest large airport to AGORI is Ireland West Airport Knock (EIKN) in Ireland.


Of course, the redispatch is a proper flight plan, so you have to put in a proper route from AGORI to EIKN. Actually, you will have to follow this route and land at EIKN if certain conditions happen that we'll talk about later.

The new computed flight plan, with the redispatch, requires less fuel for release and minimum t/o, as can be seen bellow.


So instead of 104'058 kgs of fuel, we can start the flight with only 99'383 kgs. Instead of 33'259 euros, we'll pay 31'803 euros. We saved almost 1'500 euros on this single flight. Add that to 4 flight like this per week and we can save 312'000 euros over one year from one aircraft!

Buuut, there is a catch! If you look in the above redispatch flight plan there is a bolded line that says: REQD OVER AGORI TO DEST EHAM. This is the minimum fuel you have to have on board while passing AGORI. If you have less fuel than this value, you HAVE to land at EIKN using the published route. If you don't you are flying illegally! In this example we have to have at least 20'224 kgs of fuel while passing AGORI if we want to continue to Amsterdam. And if you look a line above that you can see PLAN REMAINING OVER AGORI is 33'153 kgs of fuel which means we'll be good over AGORI to continue to Amsterdam. But this is just an estimation, you should always check your fuel when approaching the redispatch fix.

Another thing to point out is the REQD OVER AGORI TO ALTN EIKN. This means that if while passing AGORI we don't have 7'547 kgs of fuel onboard we cannot even go to EIKN and have to choose an emergency divert airport - which may be EIKN, but we are in an emergency scenario now.

Hope this helped and was entertaining and maybe will enrich your virtual world as it did mine. When I'll have the time, I'll make some manual computation and leave the step by step method for people who don't have PFPX.

Cheers,
Adrian

Offline Bogdan Ghincea

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Re: Redispatching flights
« Reply #1 on: March 30, 2016, 07:04:13 PM »
If only those were real money :)

 

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