For some reason I thought Cuba was off by 1 hour from US EST/EDT. I stand corrected.

If you are counting flying through airspace which happens to be in the same time zone, it's an almost impossible thing to determine since winds on any given day could change the flight path. Plus it's an absurd distinction - the key is that the departure and arrival airports are in the same time zone. Otherwise, you may as well rule out places which have the same time but give different names to their time zones.

My criteria is if I don't have to change my watch upon arrival I am in the same time zone.

That’s what I was thinking of when I posed the question.

Not that I've done it, but Perth to Beijing (assuming that this flight existed in the past) would probably win this one.

At least by great-circle distances, JFK-SCL (5097 miles) does in fact just beat out PER-PEK (4,954 miles), and I believe is actually currently operated by LATAM.

I suppose that works with DST. Otherwise, SCL is normally an hour ahead of JFK.

Guys, don't you read? The post stating MUC-JNB with 5200mi beats both routes.

I did FRA-CPT with LH at 5815mi.

Was it Air Namibia that did not fly over land for some time due to some disputes? Then WDH-FRA could have been actually longer...

SCL-YYZ (AC route) is 5,332 miles, longer than SCL-JFK.

I've got AMS-CPT coming up in the winter that clocks in at 5998mi on gcmap. The actual flight route seems to come in at just over 6000.

Did you read? Where did I say that JFK-SCL was the longest route? I was just pointing out that there was a route (actually in service) that was longer than PER-PEK.

I think the Apple Watch automatically changes to the correct time once there's a connection...

It seems that going north or south works best for staying in the same time zone. But does the mileage count for an air-turnback as well?

Hmmmm. Forgot about that one, which I actually flew in Northern Hemisphere summer years ago (so typically the same hour in both places).

SIN-PEK, 2,780 mi

The farthest I think possible on scheduled service on one flight would be the CZ354 pre-pandemic, SIN-CAN-SHE and the SIN-TAO-SHE measuring at 3,027 and 3,028 mi respectively, on more than one flight, maybe SIN-CAN-URC-KHG? CZ3040 and the CZ dreamliner service between CAN and KHG.