What's the cheapest flight in the world per kilometer traveled?

Question

We already have a question about the cheapest flight overall, however that only covers the total amount paid for the whole journey. I am instead interested to know which route is the cheapest in the world per kilometer traveled on board. To clarify the conditions of this questions:

• The flight must be scheduled, rather than a one time event
• The journey must take place between airports that have an IATA code
• The flight must be bookable on Google Flights or Kayak for the price you quote in your answer
• The price you quote must be stable over at least a couple of months, meaning one could reasonably book such a trip without waiting for special promotions
• If round trip tickets are cheaper, you can divide the price by two to get the per-leg cost
• Here "distance" refers to the Great Circle route between the two airports, not the actual route of the aircraft
• If the flight has more than one leg, you can only use the distance between the starting airport and the destination airport, regardless of any intermediate layovers

Answer 1

Interesting problem. "Non-stop" flights are often priced higher than connections (even if they include the same non-stop leg) simply because they can. Sticking with mainline carriers, you have to find a route that's long and has enough non-stop competition to keep prices low.

Mainline: Bejing/SYD r/t in Oct. $425 on Kayak with Air China, 8942 km times 2 or for 2.37 US cent/km. That's a good route since Qantas ($455) and China Eastern do this as well. Xiamen and Sichuan offer the same route for under $350 but there are stop-overs.

Cheap carriers: Ryan Air offers a one way from Dublin to Bremen for $15.34 (late June). It's a 1001 km so that comes out to be 1.5c/km. Other options are Vienna and Lodz which are also in the 1.3c-1.5c/km range.

EDIT: The Ryan Air flight from DUB to Bremen shows actually up in Google flights (June 26) for $16, so I think that counts

Answer 2

Well, I'll kick this off by suggesting the same answer as I did in the other question: the subsidized domestic fare for flying from Ashgabat to Balkanabad in Turkmenistan is 38 Turkmen manat for 385 km, which comes to USD 0.0052/km at the February 2018 black market rate of 14 TMT to the dollar.

No, you can't book that on Google Flights, but IMHO this condition is unnecessarily restrictive since it'll also exclude the vast majority of some low-cost carriers (edit: Huh, looks like their coverage has improved a lot since I last checked!).