Flight Narita International Airport departs from Tokyo Narita International Airport at 17:45 and arrives at Ho Chi Minh City Tan Son Nhat International Airport at 22:25.
The flighttime is about 6h 40m. The distance travelled ("as the bird flies"): 3981 Km. So the average speed is roughly 597 Km.
There is an 2 hour time difference between Tokyo and Ho Chi Minh City
