# 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.

• I think this should be merged with east/west, since any general method for finding one will also handle the other, and it would be best to have all discussions of such things on one page. Dec 14, 2017 at 1:05
• The answer to both of your questions as they stand now is: Westray and Papa Westray airports, which have nearly the same latitude and longtitude. You should probably calculate the actual angle between the longtitude and the straight line between the airports, not just the difference in latitude/longtitude. Dec 14, 2017 at 1:07
• @JonathanReez why would the angle matter for east west? Or North South? If they're on exactly the same line, that's 'straight', no? (ignoring the spherical curve of the earth) Dec 14, 2017 at 1:08
• @NateEldredge see your point, but different searchable questions. I thought of the east one while flying and googled it Dec 14, 2017 at 1:09
• @JonathanReez can see that that might be the answer given the close proximity, but it's entirely possible there's another pair that are more closely on the same line of lat/long Dec 14, 2017 at 1:10

I have a database of OpenFlights data laying around from What's the quickest route between antipodes using regularly scheduled transit?, so let's put it to work.

[an excruciatingly boring period ensues wherein we discover that PostgreSQL got upgraded on my system, leaving a database that is incompatible with the new version, and entirely too much nonsense is involved in sorting it out.]

After preparing a scratch table:

SELECT ST_X(source_geom) as src_x, ST_X(destination_geom) as dst_x, abs(ST_X(source_geom)-ST_X(destination_geom)) as delta, * from flights order by delta limit 20;

For some reason, OpenFlights thinks that "Illinois Airways" operates a flight that both arrives and departs PKN airport in Indonesia. We'll remove that, along with duplicate/reverse city pairs, including those operated by multiple airlines/codeshares to get a few top results:

'-68.2080993652344','-68.2043991088867','0.00370025634765625','Air Canada','YBC','YYY' '106.652000427','106.65599823','0.00399780299999009','Vietnam Airlines','CGK','SGN' '-81.7552032470703','-81.7595977783203','0.00439453125','Silver Airways (3M)','EYW','RSW' '-2.90027999878','-2.90499997138977','0.0047199726097702','Linhas A','KOI','PPW' '-111.983001708984','-111.977996826172','0.0050048828125','Delta Air Lines','SLC','HLN' '-94.0650024414062','-94.0708007812','0.005798339793742','Canadian North','YEK','YYQ' '139.779999','139.785995483','0.00599648299998989','All Nippon Airways','HAC','HND'

This gives our winner, flights between Baie-Comeau Airport and Mont-Joli Airport, both in Quebec, Canada. FlightAware tells me this is Air Canada Jazz JZA8968/JZA8964, nearly a straight shot north-south across the St. Lawrence River, a distance of 59km and a difference of just 0.0037 in longitude.

This is entirely based on the coordinates of the airports in the OpenFlights database, not the actual route of the flights, which will vary due to the usual flight planning considerations.

Update: I was curious what happens if instead of directly comparing coordinates, we go by azimuth instead, as JonathanReez suggested. This method gives us CGK-SGN (Jakarta-Saigon/Ho Chi Minh), the runner-up from the coordinate-based approach, with a bearing between the airports of 179.986.

This approach also produces candidates with greater degree differences closer to the poles, such as YQR-DEN. The bearing is -179.970 even though the coordinate difference is about 25", since the lines get closer together as you approach the poles.

• Now that's a great answer! Dec 14, 2017 at 5:59
• 1. Since all lines of longitude are great circles, the great circle route between any two airports of nearly the same longitude will not be perceptibly different from a line of constant bearing. Only flight planning considerations will be relevant. 2. If you also compare with airports at +/-180 degrees as suggested by Kate Gregory, does that change the results? Dec 14, 2017 at 6:41
• @phoog Hmm, if I'm actually searching for airports +/-180 degrees correctly, which I'm not entirely sure I am, I get some really fun long matches like SFO-DXB, which is 2.26 degrees off. Nowhere near a winner, but impressively straight for a 15-16 hour flight. Dec 14, 2017 at 7:00
• The route's not flown this year, but as recently as last year, there were YQR-DEN flights, which are 0.0179 degrees apart. Dec 14, 2017 at 15:41
• SFO-SEA is the first candidate that came to mind for me. If the calculator at movable-type.co.uk/scripts/latlong.html is correct the bearing from SFO to SEA is about 0.25 degrees, and this is a frequently flown route. (But so is CGK-SGN.) Dec 15, 2017 at 18:26