關於飛機路線一問

It depends on the destination in the US.

The route you describe - over China, Mongolia, Russia and the Artic ocean - is common for direct flights from HKG to the east coast USA such as JFK / EWR.

Flights to the west coast USA (eg SFO, LAX) will typically follow a flight path over the northern pacific ocean.

Other factors that play a role in determining the actual flight path include the load/weight of the aircraft, the type of aircraft used, together with local wind and weather conditions.

It's probably easier to understand if you look at the flight path from a different angle, say, from space looking down at the north pole.

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The top line is the path of shortest distance between HK and Los Angeles.
The middle line is the path of shortest distance between HK and Vancouver.
The bottom line is the path of shortest distance between HK and New York.

All three are actually straight lines on a curved surface.

this is the shortest distance

因為呢個距離係最短o既~~~
地球係橢圓形,赤道個位係最闊,而南北極係最平,所以個距離係最近o既~~~