Solution to A Puzzle with the Answer YOUKILIS

Author: Chieu Nguyen

The puzzle consists of 16 flights, each between two airports indicated by their 3-letter IATA codes, along with a distance in kilometers. If sorted by the first airport code (as is given), then the first letter of the second airport in each pair forms part of a message: these spell out ANSWER IS YOUKILIS.

In four of the flights, the distance given is exactly the great circle distance between the two airports, but in the others, the distance given is much shorter than the real distance ... it is actually half the circumference of the Earth minus the real distance. In the pairs where there is a discrepancy, the two distances add up to about 20,000 km; there is some variation here because the Earth is not exactly a sphere and is slightly wider than it is tall.

IATA codeLocationLatitudeLongitudeActual distance (km)Given distance (km)
BLTBlackwater, Australia23.60° S148.81° E160693942
ASIGeorgetown, St Helena, Ascension and Tristan da Cunha7.97° S14.39° W
CFGCienfuegos, Cuba22.15° N80.41° W14591459
NOBNosara, Costa Rica9.98° N85.65° W
DJBJambi, Indonesia1.64° S103.64° E176652340
SNUSanta Clara, Cuba22.49° N79.94° W
DOHDoha, Qatar25.26° N51.57° E47764776
WAMAmbatondrazaka, Madagascar17.80° S48.43° E
DOPDolpa, Nepal28.99° N82.82° E163373689
EZEEzeiza, Argentina34.82° S58.54° W
GVRGovernador Valadares, Brazil18.90° S41.98° W151384869
ROKRockhampton, Australia23.38° S150.48° E
KDMKaadedhdhoo, Maldives0.49° N73.00° E170412963
IPCHanga Roa, Chile27.16° S109.42° W
KHWKhwai River Lodge, Botswana19.15° S23.79° E31853185
SRHSarh, Chad9.14° N18.37° E
MAOManaus, Brazil3.04° S60.05° W161623846
YGJYonago, Japan35.49° N133.24° E
NAWNarathiwat, Thailand6.52° N101.74° E54785478
OHEMohe, China52.91° N122.43° E
PIUPiura, Peru5.21° S80.62° W155624444
URCÜrümqi, China43.91° N87.47° E
PMRPalmerston North, New Zealand40.32° S175.62° E166283379
KANKano, Nigeria12.05° N8.52° E
SHCShire, Ethiopia14.08° N38.27° E159954013
ITOHilo, United States19.72° N155.05° W
TNDTrinidad, Cuba21.79° N80.00° W185781455
LEAExmouth, Australia22.24° S114.09° E
TWUTawau, Malaysia4.31° N118.12° E172712760
IOSIlhéus, Brazil14.82° S39.03° W
XMHManihi, French Polynesia14.44° S146.07° W161113900
SMSSainte Marie, Madagascar17.09° S49.82° E

This suggests that the flights are not connecting points on the surface of the real spherical Earth but rather on the surface of an alternate Earth that is topologically a projective plane (also hinted in the flavortext), specifically the one where every point on the surface of the real Earth is equated with its antipode, the point on the opposite side.

Plotting these paths on a map of the alternate Earth yields a message, seen here in an azimuthal-equidistant projection:

It is also possible to plot the paths on the surface of the real Earth, but replacing points with antipodes so that all the paths end up on the same hemisphere, or to plot two paths for every path, one on each hemisphere.

Since there is no inherent orientation to the projective-plane Earth, there is an additional arrow to confirm the message, due to the possibility of reading it upside-down, flipped, and/or out of order. The intended message (and the title of the puzzle) is MIAMI, and the arrow points roughly to the city of Miami, Florida, United States.