While tracking the flight my wife and son are on, PR127 JFK -> MNL (which happened to swap out A359 for 77W), I notice a northeasterly heading to Greenland where the Great Circle route is the traditional western route towards northern Alaska.
What are reasons for such a routing contrary to the great circle? My guess would be the benefits of tailwinds outweigh the negatives of (slightly) longer route?
Any thoughts from the A-Net community would be most welcome. Thanks
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- davidjohnson6
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Re: Why not always fly the Great Circle route?
Weather - not just wind, but storms as well. Hurricanes/typhoons don't mix well with aircraft
Conflict - flying over regions where missiles are potentially in use
Politics - a country can close its airspace to anyone at any time
Regulatory instructions / sanctions - some countries may forbid their airlines from overflying another country
Cost of flying over a country - sometimes cheaper to fly around a state with higher charges
Potential diversion - need to be able to access a runway for landing within a limited period of time if anything goes wrong
Desire to stay close to land - some shorthaul aircraft may not be equipped for flying a few hours over water, or airline may have a policy encouraging staying close to land, motivating a slightly longer route
Military / reserved airspace or military exercises - some airspace just isn't available to commercial aircraft
Conflict - flying over regions where missiles are potentially in use
Politics - a country can close its airspace to anyone at any time
Regulatory instructions / sanctions - some countries may forbid their airlines from overflying another country
Cost of flying over a country - sometimes cheaper to fly around a state with higher charges
Potential diversion - need to be able to access a runway for landing within a limited period of time if anything goes wrong
Desire to stay close to land - some shorthaul aircraft may not be equipped for flying a few hours over water, or airline may have a policy encouraging staying close to land, motivating a slightly longer route
Military / reserved airspace or military exercises - some airspace just isn't available to commercial aircraft
Last edited by davidjohnson6 on Fri Mar 31, 2023 12:46 pm, edited 2 times in total.
Re: Why not always fly the Great Circle route?
Winds can play a big part. The shortest route distance wise may not be the fastest/most efficient way to go. If taking this route provides some extra tail wind, it may actually be quicker (and therefore cheaper fuel wise) to go that way.
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- GalaxyFlyer
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Re: Why not always fly the Great Circle route?
Winds usually. Flight planning engines usually use minimum cost or minimum time as the primary parameter. Possible routes have to then not cross any route restrictions, such as the Russian airspace or any airspace that has very expensive overflight costs. Of course, overflight costs are considered in the minimum cost routing,
Re: Why not always fly the Great Circle route?
A great example of this is the Singapore Airlines flights to NY, which on the outbound from SIN often follow close to the great circle route but on the return leave to go over Northern Europe to take advantage of tailwinds, leadng to actual flight distances sometimes $1,000 miles farther then the gc route. It ends up being faster and using less fuel though because the winds make such a huge difference.
Re: Why not always fly the Great Circle route?
Great responses! Thanks guys
Re: Why not always fly the Great Circle route?
Airspace restrictions, especially for Chinese Flights, A CAN-URC will generally take you CAN-CKG-LHW-DNH-URC
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- Latachaudhary44
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Re: Why not always fly the Great Circle route?
It's because planes travel along the shortest route in a 3-dimensional space. This route is called a geodesic or great circle route.
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- GalaxyFlyer
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Re: Why not always fly the Great Circle route?
Latachaudhary44 wrote:It's because planes travel along the shortest route in a 3-dimensional space. This route is called a geodesic or great circle route.
Not completely true, planes fly minimum time routes modified by airspace considerations. The GC route often is close to minimum time, which burns the least fuel, has lowest crew and maintenance cost; but winds can dictate a fairly large variation.
Re: Why not always fly the Great Circle route?
Also, near the edges of a map,due to the curving nature of earth, distances are closer apart under the same distance in the map. Hence, with SIN-JFK, there are many ways of flying.
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- Starlionblue
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Re: Why not always fly the Great Circle route?
rt23456p wrote:Also, near the edges of a map,due to the curving nature of earth, distances are closer apart under the same distance in the map. Hence, with SIN-JFK, there are many ways of flying.
This depends on your map projection.
The reason there are several ways of flying SIN-JFK is due to winds, diversion options, and overflight fees. It has nothing to do with maps. Maps don't change the shape of the Earth.
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- AAPilot48Heavy
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Re: Why not always fly the Great Circle route?
Starlionblue wrote:rt23456p I wrote:Also, near the edges of a map,due to the curving nature of earth, distances are closer apart under the same distance in the map. Hence, with SIN-JFK, there are many ways of flying.
This depends on your map projection.
The reason there are several ways of flying SIN-JFK is due to winds, diversion options, and overflight fees. It has nothing to do with maps. Maps don't change the shape of the Earth.
I’ve often wondered how all this works, given that the earth is actually flat. It leads tona lot of fascinating discussion and observations on flight paths.
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- Starlionblue
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Re: Why not always fly the Great Circle route?
AAPilot48Heavy wrote:Starlionblue wrote:rt23456p I wrote:Also, near the edges of a map,due to the curving nature of earth, distances are closer apart under the same distance in the map. Hence, with SIN-JFK, there are many ways of flying.
This depends on your map projection.
The reason there are several ways of flying SIN-JFK is due to winds, diversion options, and overflight fees. It has nothing to do with maps. Maps don't change the shape of the Earth.
I’ve often wondered how all this works, given that the earth is actually flat. It leads tona lot of fascinating discussion and observations on flight paths.
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- AAPilot48Heavy
- Posts: 274
- Joined:
Re: Why not always fly the Great Circle route?
Starlionblue wrote:AAPilot48Heavy wrote:Starlionblue wrote:
This depends on your map projection.
The reason there are several ways of flying SIN-JFK is due to winds, diversion options, and overflight fees. It has nothing to do with maps. Maps don't change the shape of the Earth.
I’ve often wondered how all this works, given that the earth is actually flat. It leads tona lot of fascinating discussion and observations on flight paths.
