sebavasta
Topic Author
Posts: 1
Joined: Thu Aug 29, 2019 3:24 am

Do airlines use full range of an aircraft when planning routes

Fri Aug 30, 2019 7:40 am

Hi, I am an aviation enthusiast. My question is this (I am talking 777-200 as an example):

Boeing 777-200 (not ER or LR, just the plain -200) has a listed range (in Wikipedia) of 9700 km.

Now suppose distance from city A to B is 9500 km. Will the -200 be allowed to fly??

Suppose distance between city C and D is 9690 km. Will the -200 be allowed to fly between C and D
with only 10 km left of the maximum range the plane can go?

Basically what I want to know is how trips are planned.

Is there a percentage like 10% or 20 % you keep off the range of an aircraft when planning routes??
Like for example for the -200 you keep 10% of the range as the distance it can travel. Although -200
can travel 9700 km airlines only let the -200 travel 8730 km. I.e. They keep 10% of the range for safety or other concerns??

Is this it or -200 can travel to a city 9700 km away (i.e. full range)??
 
gloom
Posts: 303
Joined: Thu Jun 30, 2016 4:24 pm

Re: Do airlines use full range of an aircraft when planning routes

Fri Aug 30, 2019 8:03 am

It's much more complicated.

There are many things you need to consider.

First, planes do not travel straight lines. They will travel on routes, or between points on route. That adds a few percent to the route (more on shorter hops, less on longer hops).
Second. there are winds. They're measured all the time, so when planning a route you can calculate what route would be "shortest". However, sometimes you're up against the wind, so you'll have to fly longer (and farther) since plane is "pushed back " by the wind.
Third, for safety you need to be close to the airports on route in case of any problem. There's quite a knowledge behind this, but to keep it simple sometimes you need to be close to airport and it would mean extra deviation from shortest route.
Fourth, at the end you need to have some extra fuel. Just to be on a safe side. This would in some cases imply you might need to take more fuel than the estimation given in producer range. Similar case is your own airplane weight. It could be a couple of tons heavier than what producer specifies, since you wanted some extra stuff for passengers, for example.
Fifth, sometimes you need to fly on non-optimal altitude. It could not be available for many reasons, operational, other traffic, whatever. It would make your plane burn more fuel, effectively reducing your range.

The airlines do have an access to all the data when talking to the manufacturer, they know where they'd like to deploy the plane, and they have clear data whether they will make it with viable load, or not. By a general rule, you will not see planes going to full range, as it would require ideal conditions and no cargo at all, only full board of passengers. In most cases, the plane will be limited to 85-90% max range to be effective. This is however a rule of thumb, and for heavy cargo applications, you might see a plane with a range of say 8000km being selected from a plane with a range of 6000km for a 5000km route. The first one would simply take much more cargo.

Tried to keep it as simple as possible, without going too much into details and oversimplifying. Hopefully it worked.

Cheers,
Adam
 
flipdewaf
Posts: 2846
Joined: Thu Jul 20, 2006 6:28 am

Re: Do airlines use full range of an aircraft when planning routes

Fri Aug 30, 2019 8:45 am

It depends on soooooo many things that it ends up being a difficult question to answer. A non exhaustive list of the things that will affect range are:
Payload,
Weather on the route: Winds(direction and speed), temperatures, weather systems that need to be avoided.
Weather at the fields (departing, arriving and alternates) Wind (direction and speed), temperature, precipitation
Available runways for takeoff : including length, obstacles, suitability
Distance between suitable alternate fields for ETOPS
Performance factors on the airframe (generally gets worse over time)
Performance factors on the engine (generally gets worse over time)
Minimum equipment, you can still fly with some things missing but you need to factor it in to your calculations, i.e. you can go without a wingtip in some cases but you incur a fuel burn penalty and there are other things such as packs which will limit maximum allowable altitude and therefore affect fuel burn.
Crew duty times (both flight crew and cabin crew)
The regulatory authority under which the flight is taking place (this can affect the duty times and requirements for alternate airfields and holding times)
The route itself, this can be whether the flight goes over water or not (life jackets 50miles+?) high terrain for drift down altitudes, there is a war in the middle.

There are probably a lot more things to go at but that gives you some indication of the things that have to be though about when planning routes and I'm sure other will chime in with more.

Fred
Image
 
Sokes
Posts: 222
Joined: Sat Mar 09, 2019 4:48 pm

Re: Do airlines use full range of an aircraft when planning routes

Fri Aug 30, 2019 6:27 pm

Welcome to the community. To come to your question:

-Alternate airport: If the destination airport is closed, e.g. bad weather, one needs fuel to reach an alternate airport. That's a minor factor if one flies over Europe. But if you want to fly to Iceland and the airport closes shortly before your arrival, you may have to fly back to Scotland. Then many other requirements already spoken about.


-Engines need less maintainance if they can be used below maximum power = derated. An airline can choose a plane with different maximum takeoff weights (=MTOW). Lower MTOW is cheaper. It also lessens the landing fees. However the plane and the engines are the same. But the engines will not run at maximum power. It's called a paper derate.
If the airline some years later needs more power the airline for a (high) fee can choose the higher MTOW on their old plane.
A plane which starts below it's paper MTOW also doesn't use max engine power (of it's paper MTOW) to reduce maintainance. It can climb to high cruise altitudes faster, which saves fuel.


-I think the main factor however is cargo. In the US cargo has it's own planes flown at night, e.g. FedEx. Within Europe cargo is mostly carried by truck. US-Asia cargo often is carried by own planes with a stop in Anchorage. However if cargo is carried below 10 hour or so flights, airlines try to carry as much as possible in the belly of passenger planes. Europe-US and Europe-Arabian Gulf are just two examples.
The range Wikipedia/ aircraft manufacturer give you is with passengers and luggage only. One has to deduct reserves, wind, ...
But beyond this airlines like to carry cargo instead of fuel, e.g. A330s or B777s on six hour flights. Passengers, luggage and cargo are called payload. I'm not sure if toilet water, food and drinks and such stuff is also included in payload. The more payload, the less fuel and therefore range.
Check this page:
https://bigsynthesis.com/understandinga ... ge-diagram

I read Air Canada was using B777-300ER on routes on which they could rarely sell all seats. No problem, they had enough cargo to carry. If they can sell the seat, so much the better. I think these flights were above twelve hours, but I don't remember exactly.


-Then there is availability of planes. Roughly speaking the longest distances flown will see the youngest generation planes. Whatever plane was used earlier on these routes will be used for shorter routes. E.g. an airline may have leased a B777-300ER for 12 years for a long range route. After the 12 years the airline replaces the B777-300ER with A350. What to do with the 12 year old B777-300ER? Similary A330s are replaced with B787s. So planes may be used on routes which they were originally not designed for, if they are cheap enough on the second hand market.


To get a rough idea for which distance planes are used, see the freighter's version range. That however may only be true where passengers and cargo is carried.
Why can't the world be a little bit more autistic?
 
timz
Posts: 6567
Joined: Fri Sep 17, 1999 7:43 am

Re: Do airlines use full range of an aircraft when planning routes

Fri Aug 30, 2019 6:47 pm

sebavasta wrote:
Boeing 777-200 (not ER or LR, just the plain -200) has a listed range (in Wikipedia) of 9700 km.


Any time someone says such-and-such aircraft has a "listed range" of so-and-so kilometers, pay no attention. They're not telling you anything helpful.

But if they say it has a range of so-and-so km with a payload of so-and-so kilograms, and normal reserve fuel -- that's helpful. Like any other airliner, the 777 can fly farther if it's only carrying half its allowed payload.
 
GalaxyFlyer
Posts: 3518
Joined: Fri Jan 01, 2016 4:44 am

Re: Do airlines use full range of an aircraft when planning routes

Fri Aug 30, 2019 7:45 pm

Even more helpful is, “this plane can fly 12 hours at M.85; 13 hours at LRC.”
 
GalaxyFlyer
Posts: 3518
Joined: Fri Jan 01, 2016 4:44 am

Re: Do airlines use full range of an aircraft when planning routes

Fri Aug 30, 2019 7:47 pm

Even more helpful is, “this plane can fly 12 hours at M.85; 13 hours at LRC with xxx payload and normal reserves”. Add in Boeing 85% winds on a specific route, helps. Planes fly by time, not distance.
 
thepinkmachine
Posts: 365
Joined: Tue Apr 28, 2015 4:43 pm

Re: Do airlines use full range of an aircraft when planning routes

Fri Aug 30, 2019 9:51 pm

Rather than asking “what range this airplane can fly” airlines ask “how much payload this airplane can take from A to B” and “how much fuel it will burn carrying xxx tons of payload for a given distance”

I fly 787 for a living (heck, as a captain!) and I have no idea what the range of this thing is :)

It isn’t published any manual I have. All I know is how much fuel it takes to fly a given distance at a given landing weight....
 
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zeke
Posts: 13903
Joined: Thu Dec 14, 2006 1:42 pm

Re: Do airlines use full range of an aircraft when planning routes

Fri Aug 30, 2019 11:34 pm

sebavasta wrote:
Basically what I want to know is how trips are planned


Most airlines will not select an aircraft based upon a single route, a network approach is adopted.

No aircraft is perfect for every route, what is more common is to look at what the aircraft will earn and what it will cost to operate the aircraft over the whole network given historical variations in payload and winds.

The same analysis is done for other types over the network.

Once all that is done a net present value analysis can be done including the finance costs, purchase cost, maintenance costs, spares, training etc.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
JayinKitsap
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Joined: Sat Nov 26, 2005 9:55 am

Re: Do airlines use full range of an aircraft when planning routes

Sat Aug 31, 2019 6:37 am

Each model has an airport planning guide. I have the link below to the 787 guide. In part 3-2 it has the payload-range charts. It identifies for a standard day (sea level, 70F) the Max zero fuel weight, and a series of lines for various MTOW sloping down, the longest range has a clip where the maximum weight of fuel on board is hit. So for a given payload and MTOW the expected range is listed. These are generally good but airlines have actual data to feed the programs.

https://www.boeing.com/resources/boeing ... ps/787.pdf

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