What's the least difference in longitude on a flight between a pair of IATA airports?

The obvious partner to this question : What's the 'straightest' east-west flight?:

I flew from CBR - Canberra [35.2809° S, 149.1300° E] to ADL - Adelaide [34.9285° S, 138.6007° E] on Tuesday and noticed on the inflight map that it was very close to being perfectly west. As you can see from the lat/long pairs, it's not far off.

I was wondering what the closest to a straight-line pair of airports was, north to south (or south to north) that actually have flights between them?

To avoid same-city airports or terminals, the pair should be at least 50km apart. To clarify, the difference between A and B is 0.x deg longitude. The 'straightest north-south(or south-north) would have the smallest difference in degrees longitude.