The flight.dat files controls the movements of NPC airborne vehicles in GTA III and Vice City. These files are located in the data/paths folder in the GTA3 III or Vice City directory. The
flight.dat controls the Airtrains. The
flight2.dat controls the DeadDodo. The
flight3.dat controls the DeadDodo used in "S.A.M. " in GTA III and the slide-door Police Mavericks in Vice City. The
flight4.dat controls the DeadDodo used in "A Drop In The Ocean" in GTA III. These airborne vehicles are not solid so you cannot collide into them and there are no drivers in them.
The file starts with the number of coordinates that will be used in the file. The rest of the file contains the X, Y, and Z coordinates linked as a path in the game.
The following is for GTA III only. Opcode 0358 is used to create the Dodo in GTA III to follow the path from the flight4.dat file. Opcode 0359 checks if the Dodo is destroyed. Opcode 033A creates the Dodo in GTA3 to follow the path from the flight3.dat file. Opcode 033B checks if the Dodo landed on the ground and opcode 033C checks if the Dodo is destroyed. Opcode 035A gets the coordinates of both of the Dodos.
Not much is known about these files other than what is above.