kash

Just curious. As I was surprised by how long it took to fly from SFO to Sydney.

lucky9876coins

Hmm, not sure if I know exactly what you mean. Typically on a long, transoceanic flight like SFO-SYD it's almost the most direct routing that's flown. Keep in mind the earth is round () so what appears to be a curved line on a map can actually be the fastest distance. I know in many cases it's nowhere even near the fastest direct distance, but in the case of SFO-SYD I think it's pretty close.

Rejuvenated

Here's what SFO-SYD looks like on the GC Map.

Ted S

Interesting question. I'm taking a short domestic trip this evening so I figured I'd pull it up and compare against the map... SNA to OAK. Can't get much more direct than that. Of course I've also been on routes that I swear were dramatically different [and shorter] previously with the same weather conditions.

Donut13

Your forgetting about the wind, sometimes by flying a 100 miles out of the way you can still save 2 hours

TA

maybe the OP is asking a subtle geometry question and means if the plane could fly in a straight line right through the earth. For SFO-SYD, it would only be a 15% distance savings...

or maybe he is not being that clever and just confused by the projection. You can see in this alternative map projection that it is a straight line:
http://gc.kls2.com/cgi-bin/gc?PATH=S...MAP-CENTER=SFO

nd_eric_77

This is correct; the geometry of spherical surfaces is quite different than the geometry of flat shapes. When viewed against a map, this only becomes evident when one is flying a non-negligible percentage of the circumference of the earth. Non-euclidian geometry in action!
This is also very true. On Tpac routes, prevailing winds often lead to a scheduled difference of flight time of 2 hrs or more. On Tatl flights, the flight path can vary widely as airplanes go out of their way to avoid the jetstream (particularly for westbound flights.)

oneant

Actually, a great circle (or segment thereof) IS a straight line. It's just in curved space-time.

Loren Pechtel

Yeah, it's very dramatic on SFO-PVG. Westbound it flies the great circle route. Eastbound it comes on a much more southernly route--longer but it's still a shorter flight.

undersky

you are right! if you point a laser beam in SFO toward the direction of SYD, and if someone is looking at the beam from moon, that person would see the laser beam "bending around" the earth surface to SYD, although to laser beam itself, it's going a straight line in its curved space-line!

nimeta

Don't forget that in busy areas (e.g. across US or Europe) there are congestion issues to deal with. I am not an expert, but if everyone flew in a straight line it could be very difficult to guarantee no mid-air collisions. I always assumed there were routes that were designated to make air traffic controls job manageable. Maybe someone here knows if this is true??

El Cochinito

True. At a real basic level, aircraft navigate along designated routes called airways between navigation beacons (VOR = VHF Omnidirectional Range beacons or NDB = Non-Directional Beacons). There are low altitude airways used below 18,000 feet - these are designated with the letter "V" on charts followed by a number - that "connect" beacons. There are high altitude airways or jet routes which have the letter "J" followed by a number on high altitude charts which also run between beacons. VORs and NDBs are named and have their own designations on charts.

For example, a United flight from Sacramento to Denver might file a flight plan to use the DUDES9 departure procedure (which defines HOW to properly leave Sacramento International Airport on an easterly route), fly to the Mina VOR beacon in Nevada, then follow the J84 high altitude jetway to the Meeker VOR beacon in Colorado, then use the TOMSN4 (Thompson-4) arrival procedure which governs arrivals from Meeker into Denver International Airport.

Occasionally flight crews will try to get more direct routing with a request to Air Traffic Control. For example flying from Chicago or Denver back to Sacramento flight crews might ask, enroute, for "direct to Squaw Valley", which is the VOR near north Lake Tahoe and the starting point for descents into Sacramento. If they are granted "direct Squaw Valley" from ATC (which depends on weather, traffic, and whether or not the military restricted airspace which takes up a big chunk of central Nevada is in use or not), then the trip goes a bit faster because it's more of a straight line.

I'm not a pilot; learned all the above listening to ATC on United's channel 9 over the years and hanging around Flyertalk.

flyingfkb

I know that Lufthansa spend a lot of money and time talking with the Chinese Government to improve the flight routes over China. They can save now I think 20 minutes flight time. The articel was in the December Issue of Lufthansa's Inflight Magazine. There are probably flight paths in the US that could be optimized, too.

m60521

You'd probably have to fly around the world several times before you'd arrive at your destination, unless they had runways pointing in every direction.

Would you accept turning the steering wheel just a little bit?



Ok, a real answer. For long trips, try pulling a string from point A to point B on a globe. The curvature of the earth on flat maps only looks like the route is not direct. Other than traffic routing and wind/weather routing, the path taken is usually very direct.

tev9999

You also have to consider ETOPs, especially on ocean going routes. The plane always has to be within X minutes of a suitable airport in case of engine failure or other emergencies.