Can we fly either direction to Asia from USA?

You can go east or west (or as has been pointed out, more north.) It depends on where in the USA you start out from (as well as where in Asia you're going) which way makes the most sense. But what airline you travel on is actually going to determine which way you go.

The airline you choose will be the biggest factor in determining which direction you fly. Almost all the Asian airlines will fly over the Pacific, even from the US east coast to countries like Thailand. All Asian airlines and many American carriers do not fly non-stop to Thailand, they will layover in other Asian cities such as Hong Kong, Tokyo, Seoul, Taipei, etc. before continuting on to Bangkok. The world's longest non-stop flight from Newark to Singapore on Singapore Airlines takes a polar route across the North Pacific and doesn't come close to California. On some airlines, you could choose a flight that had a layover in California though.

If you were to fly on a European, Middle Eastern and some American carriers, you will fly across the Atlantic and have a layover in Europe or the Middle East before reaching Thailand.

If you were to look at a globe of the world, Thailand is about halfway around the world from the US east coast, but it's the airline and flight you choose more than any other factor that will determine which direction you fly. It would be much longer to travel to most other Asian cities across the Atlantic, and from the west coast, much longer.

There are more than just one factor that determines flight routes, although I doubt the earth's rotation has much of an impact ... except to the jet-lag a traveller feels once he lands :p

Distance is definitely a consideration as well as the fuel costs. The cost per unit of distance is apparently greater for shorter distances than it is for longer ones because of the amount of fuel burned for a sharper ascend in the case of the former compared to a gradual climb for the latter. Another consideration, particularly for non-direct flights is the demand for any particular leg of travel. If there are more people wanting to travel to a city en route in one direction, then the availability of that route is higher than a route in the opposite direction.

Then there are the international agreements as to which airline can land into any particular country's airport ...

But if you are a bird and do not need to rely on international airspace and the agreements to enter airports or do not have to worry about fuel costs, yes, you can pretty much travel any direction.

I think your mention about the rotation of the earth is because you are thinking of something like climbing up on a downward escalator ... if you go faster than the escalator though, you can still reach the top.

I think distance is the main determining factor. There are fuel costs involved so airlines will go the shortest way possible. If flying east from JFK to Thailand is longer, then they will go the other way to use less fuel. The longer the distance, the more fuel you use. Its kind of like driving, except the shorter distance usually takes less time. Earth's rotation doesnt really factor into it because the Earth only spins in one direction and it doesnt have anything preventing a plane from going in the opposite direction

I think it depends on the airline and where you are flying from. Singapore Airlines flies from Newark Liberty in New Jersey to Singapore non-stop. However they fly towards the Pacific Ocean. Singapore Airlines also offers a flight out of New York JFK International to Singapore but you fly towards Europe. You actually connect in Frankfurt.

Thai Airways flies to Los Angeles so it would make more sense for them to fly over the Pacific Ocean. Most airlines that fly out of the west coast cities to Asia would fly over the Pacific Ocean. Airlines flying out of the east coast will vary. Some airlines such as China Airlines will stop in Alaska to refuel and continue on. Other airlines such as Malaysia Airlines will fly towards Europe.

As for the determining factor, distance plays a big part as jet fuel is quite expensive. Another factor may be the demand and competition for a certain route if the airline flew in one particular direction. For example, Singapore Airlines flies between New York to Frankfurt to Singapore. Maybe they chose Frankfurt as a stopover/refueling city because they know a lot of business travelers will fly that route or that there are not that many airlines flying between New York and Frankfurt as opposed to New York and London.

Fly To Asia

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Distance is ultimately the factor in which way a plane will fly -- flights from East Asia to the US are likelier to fly over the Pacific because it's shorter to go that way, but from the Middle East, they'll go over the Atlantic.

A flight from New York to Bangkok, however, won't fly over the Pacific -- as illustrated by the link below, it will actually fly the polar route over Canada and Russia, as it's far shorter to go north and then south than it is to go west.

Well, you also have to remember that Saudi Arabia is also Asia, which is closer when going to the east from NYC.

The Earth's rotation has nothing to do because the air moves along with it. Otherwise, there'd be no life on earth, just very very turbulent winds.

Also, because the geometry is different, the routes taken are curved as they get farther.

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