Though serviceable, this aircraft has been far outclassed by more modern developments in aviation technology.
Game Effect: Antique aircraft have speed, structure and acceleration levels 1 level lower than purchased, to a minimum of one. Antique planes must purchase level 2 or higher in a trait.
Cost: Antique decreases the cost of the airframe and the engine by 20%
This should hopefully help represent the older planes with lower performance figures.
EDIT: Changed cost effect at Grant's suggestion.
I think this will work better.