Flight Paths...
 

Who designs flight paths? Each airline or someone else?

I'm interested to why (for example) the LHR-LAS flight path looks like this (super curved).... Is there a science behind it? Is it simply to avoid other flights? How do they decide which flights to lengthen?

Boring Sunday snowed in got my small brain ticking :D

https://cimg8.ibsrv.net/gimg/www.fly...705f436bcc.jpg

Curvature and jetstreams will dictate this

Remember the flight path in this example is curved as this is the shortest route, as the world is not flat.

Brian

Isn't that contributed to by the fact that the earth is not flat?

Google Great Circle Route

Don't feel stupid! It's just to do with difficulties with representing a near-spherical object on a flat surface, which is utterly not your fault* and really, they should draw the rhumb line or something so that it doesn't look like the flight took a very strange curvy path :D

There's a society for people like you ;)

Honestly, don't feel daft. I didn't understand it without explanation at first. When I was younger and first flew UK - US via AMS, I didn't get why we flew down to then fly all the way back up over where we'd just come from. Obviously that was also to do with flight availability and price, but still..:D

Bit of a long read but this is interesting: https://nats.aero/blog/2014/06/north...ateway-europe/

NATS basically design 'tracks' each day depending on the jetstream. Each aircraft then gets assigned a track.

I love how all of you believe that "round earth" stuff!

One other factor about this route is that it passed through Canadian airspace. Canadian airspace is more expensive to travel through than, say, US airspace (in some cases).

The slight flattening of the curve between the Canadian border and LAS may (or may not) account for this. What I mean is that the route has been slightly altered to minimise time over Canada.

I was going to post about how this route is not simply a great circle as it has a deviation to cut down on overflight fees generated by flying across Canada. Then I saw MarkFlies post above and realised he'd beat me to it.

Flights from SFO, LAX, etc. will often take a more easterly track to reduce the total cost. The airlines have sophisticated software tools that allow them to plug in all the various parameters (flight time, fuel burn, jetstream/weather conditions, overflight costs, ...) in order to map out an optimal route according to the anticipated conditions for the flight.

This video from Wendover Productions has more info on this (starting from around 4:25):

These "spherical Earther" weirdos are like a cult. If the the earth was spherical then to get to the other side of earth all you needed to do was take off, fly circuits in place and the rotation of the earth would bring you to the other side. Well we know that does not work like this, you actually have to fly somewhere to get there.

Cmon you spherical earthers. Proven science is above, weird theories...

Some airlines have their own flight planning computer time,others use bought in service.Normal parameters for a route being chosen include winds,airspace closures,overflight charges,insurance and crew costs,aircraft weight and a number of other factors.The numbers are crunched by high speed computers and usually 2 or 3 options are added with costs and fuel burn.For a B747 fuel burn is worked to the nearest 50 or 100 Kgs out of a possible 160 tonnes or so.

Like most things in aviation it is worked to minimum cost.

Well, it's not so much that the flight path is 'curved', but the map is distorted. If you viewed the path on a polar stereographic projection it would be much more a straight line (and give you a better idea of deviations from a direct route due to jet streams/etc).

You mean she charges by the hour? ;)

FWIW, the shortest (ie great circle) route from LHR to LAS can be seen here: Great Circle Mapper

Start with the great circle route, and adjust for winds. For example, I took BA48 a couple of months ago SEA-LHR. It usually heads straight NE over Canada, but the winds that day were more favorable for going E to North Dakota (ground speed of 700 knots, according to the map on the IFE) before turning north to catch the track over the Canadian Arctic/Greenland/Iceland to the UK.

But start with a globe and a piece of string.

http://www.gcmap.com/map?P=lgw-las&M...b:disc7%2b%25t
Looks like a pretty straight line to me. :D

https://skyvector.com/

I stumbled across this site the other day, with the North Atlantic tracks shown, along with other routes/paths/corridors.

Ah - rather an idealised great circle example...

Below is BA 285 LHR-SFO on 9th Dec - the first mapping is an equal area, the second a Mercator....

https://cimg0.ibsrv.net/gimg/www.fly...f60e25f90c.jpg
https://cimg1.ibsrv.net/gimg/www.fly...2f402744af.jpg
Things to note that all equal area projections aren't really equal area (!), and while Mercator is often used, it's terrible at representing the higher latitudes!

BTW - you'll probably notice (or find out) that for TATL flights westbound tend to be on more northerly routings to avoid the (headwinds of the) jet stream, while the eastbound services tend to be further south take advantage of the jet stream (tailwinds).

With regard to jetstream taken into account of the flightpath, here's a map for that route (updated every 4h):
https://earth.nullschool.net/#curren...0.74,51.96,503

Many years ago when I did a lot more flying, I was on a flight with a new colleague going to LOS. He asked why the flight time returning to LGW at the time was longer than the outbound to which my quick and witty reply was “because we’re going uphill going back”. His answer being “Oh, that makes sense” 😬

S

A despatcher once told me flight routes are also designed so that they are never more than an hour's flying time from an airport, as much as possible. So flights across South Atlantic fly close enough to the Azores. Not sure if I remember details absolutely correctly.

Said dispatcher is misinformed I'm afraid.That would burn too much fuel.Most long haul twin engine aircraft are certified for 3 hours from a diversion airport at single engine cruise speed/mach.

That's true for most two engined aircraft which are not rated for extended operations (ETOPS). You need to be within 1 hour diversion flying time on one engine to an airport. Obviously for flights across Europe is isn't an issue. However, I would imagine most aircraft used regularly for trans ocean flights would have a more relaxed requirement. A number of aircraft can be approved for ETOPS ratings where the flying time can be a lot more than 1 hours. Typically I think ETOPS 180 is common - so you can route such that you are within 180 minutes one engine flying time of a diversion airport at all times. Higher ETOPS ratings are possible to I believe.

ETOPS 180 aircraft can be wide bodies such as 777/A330, and narrow body aircraft can also be rated higher. AA uses specific ETOPS rated A321 aircraft from LAX/PHX to Hawaii for example, and BA's babybus would be ETOPS rated.

Probably better explained here https://en.wikipedia.org/wiki/ETOPS the diagram makes it a bit easier to understand.

OK that would explain it. My friend dealt with small private jets.

Hi everyone!

A friend of mine has just pointed me to a strange flight path of this flight (UKL4076) that has been waking him up, always taking this same route. The aircraft takes off from Izmir and the destination is always indicated as Kiev, Ukraine but just before there, it takes a sharp turn to later land in Liege, Belgium. This is supposed to be a military-registered aircraft so, being a total ignorant, I am just wondering whether this is common practice or there really is something strange about it.

I will appreciate any input! :-)

Damn - sorry KARFA - for some reason didn't spot your above post. Apologies.

Predictably it's a bit more complicated than that. There are all sorts of protocols for this but one that you may often see reference to is ETOPS, which stands for Extended range Twin engine Operational Performance Standards. Basically a set of operating procedures to allow twin engined airliners (where the issue or a single engine failure over water / ice is more serious than in a 4 engine bird) to operate safely.



In addition to the requirements about flight time to emergency / alternate fields (which are defined as permitted maxima at single engine cruise speed, based on the exact ETOPS certification the plane has) there are also as I understand it extra protocols around maintainence checks etc. The aircraft even have ETOPS painted on the undersides in strategic spots just so, when they're in hangar getting a look over, there's no confusion as to what needs inspecting and to what level of detail.

So in theory a non ETOPS certified plane shouldn't be flying an ETOPS routing. AA got in trouble with this a while back flying LAX to HNL and had to get another bird out there for the return.

Apparently in aviation slang it can also stand for 'Engines Turn Or Passengers Swim'. Got to love that. But it is not specifically a ruling about flights over water as I understand it - the assessment is on flight time to a suitable alternate. And therefore there are also standards for 4 engine planes (typically ETOPS 180 I think).

As you'd imagine there is lots online on this. The above is merely a summary of the small amount I know about it. If I got any of this wrong, experts please feel free to correct (gently please haha)

There are no etops requirements for 4 engine aircraft.The only requirement is for a suitable alternate.This can be limited by fuel required at 3 engine cruise such as on a trans pacific flight,or sometimes an oxygen limitation if far from anywhere and in the event of a decompression.

Apologies yes - incorrect - the restrictions and stipulations for 4 engine planes wouldn't come from ETOPS classification (the 'T' standing for twin). Poorly / confusingly written on my part. Thanks for the correction. I was however labouring under the impression that the 180m number had some significance for 4 engine planes, so I wonder where I got that from.

The map above of a LHR-SFO is about as straight as you can get. However, regularly flying the route, there is considerable variance. My northern Canadian geography is hazy but, further east you generally fly south of Iceland but it's not too infrequent that you will fly directly over Iceland, and once we were north of Iceland. Likewise, further west, you generally enter the USA over Spokane but I have come down over Portland and also much further east, flying over SLC.

The OP raised a valid point and it's triggered off some interesting responses.

I remember being a bit surprised once when my wife and I had separate but concurrent flights from LHR to Tokyo, her flight (Virgin) was non-stop and I was Swiss flying via ZUR.
I expected a shorter leg from Zurich - ( it's east of London and nearer japan, I thought)
Turned out that the flight paths mileage LHR-NRT was about 10 kilometres different from that of ZUR-NRT

That only applies to twins.Maybe that is in the back of your mind.

Actually I think more like what's discussed in the link below must have been in my thoughts. Who knows. It's hard enough for me to remember my opinions without also having to remember the reason for them.... ;-) :p :p :p


https://aviation.stackexchange.com/q...uivalent-rules

Remember, unlike that map, the Earth is curved. So when it's put into a 2D format from a 3D reality, it will come out curved. That route is a shorter distance than what a straight line on the map would appear like. The Earth is not a sphere, but more of a squashed oval. Going on a more southerly route means more distance needs to be covered.

Now, generally airlines have logistics departments that work the routing. There are many factors which determine how a flight routes, and it is rarely straight. Even with GPS and the technological ability to fly direct point to point, most planes are still routed from beacon to beacon or nav point. Factors that influence this are airspace rules (restricted spaces around military zones, or countries that don't want foreign planes in their airspace like North Korea), safety factors like distance to diversion airports or radio dead zones, weather..either avoiding the bad stuff or taking advantage of the good weather.., and fuel savings. For example, avoiding a jet stream headwind for 12 hours by going north or south of it, or above it.