Los Angeles to Hong Kong Flight Routing Conundrum

December 24, 2017 11:46 AM

This month my wife and I visited Hong Kong and China. It was a great 10 day trip. On the flight out to HKG we flew up over Siberia and then south over Mongolia, China and eventually to our destination.

However! On the way home we took a more direct route, skirting the Aleutians and winding up at LAX.

The trip out was 15+ hours and the ride home 11 and a half.

Why’d we travel the long way on the way out?

posted by notyou to Travel & Transportation (6 answers total)

Best guess is Jetstream. If that direct route had a huge headwind going and tailwind returning, that could easily make hours of difference.
posted by JMOZ at 12:07 PM on December 24, 2017 [5 favorites]

I agree that it's most likely due to the prevailing winds at high altitudes, particularly the jet stream. To support this: Here are the FlightAware pages for Cathay Pacific 885 (LAX–HKG) and Cathay Pacific 880 (HKG–LAX). If you scroll down to the "Activity Log", you can see the flight durations for the last couple of weeks, and clicking on each flight can show you the route taken.

Note that the Asia-bound flight is usually 15–16 hours, while the America-bound flight is 12–13 hours. This suggests that it wasn't a one-off issue with your flight, but is instead standard practice.
posted by Johnny Assay at 12:27 PM on December 24, 2017 [3 favorites]

Yes, it's always longer flying west from the US, due to the prevailing winds. I've flown SYD to LAX many times and there's a few hours difference.
posted by kitten magic at 2:49 PM on December 24, 2017

Response by poster: Just a note to clarify my question: I understand the prevailing wind and the effect on travel time. I don’t understand why they don’t follow the same cours to and fro (see Johnny Assay’s helpful links that show the divergence clearly).
posted by notyou at 3:53 PM on December 24, 2017

The great circle route between LAX and HKG does just skirt the Aleutians, so you are correct that the route back was shorter. But, if there was a 200 mph headwind along that shortest route (which isn't unheard of), it was faster to take a longer route at a quicker speed. Airlines have meteorology departments to figure this out, since they won't waste a drop of fuel if they don't have to.
posted by hwyengr at 3:55 PM on December 24, 2017 [2 favorites]

Thinking about that more to try to clarify it, if there was a route where the headwinds aloft were only 100mph instead of 200mph, on a 15 hour flight you could fly an extra 1500 miles and arrive at the same time as the shortest route. Any alternate routing that is less than 1500 miles longer is a net positive. If it was longer than that, they'd just fly into the strongest winds on the shortest route.
posted by hwyengr at 4:09 PM on December 24, 2017 [3 favorites]