Air Traffic Controller

This can be done during Hive Extermination (Northeast Strike)

Two tricks:
1) Falling jellies can be hit multiple times when falling, so fly back into them. Sometimes these even count as 2.
2) There is a short period after the first objective completes where jellies can still be hit, even though they don't count for anything.

With these two tricks, you can finish this in 1 strike so you don't have to wait for a new cycle.

Can be done in Eversong at the void strike at 34.84 78.73

This can be completed during three "Hive Extermination" void assaults (one in Eversong Woods, two in Zul'Aman, so you can farm the achievement during both weeks) at the following spots:

/way #2395 35 77
/way #2437 54 20
/way #2437 53 81

Just fly through the various enemies 50 times.