This is missable and you can get this one in Chapter 1-3, you will come to a hill and the Iron Whale will come down, Bo will shout "Transport" and from here all you have to do is shoot the engines/turbines. Don’t be confused the first battle with an aircraft that has 4 engines that you must destroy is NOT an Iron Whale, it is an Iron Raptor and is more of a fighter style aircraft. The Iron Whale looks similar but is just a transport vehicle. It comes out when you are defending Bo and Charlie on the zipline with Cain. Just use your assault rifle on each engine/turbine; they are surprisingly weak so you should get this no problem.
No it is not its the random transport ships that drop off enemies, no real trick to it, just got to be fast i did it with the standard assualt rifle at some point, but i know the sniper destroys 1 engine with 2 bullets, im guessing a rocket launcher must be good for this, but its pretty easy
Found it very easy to do at chapter 2:2 whilst you waiting of the robot to fuel something.
The transport carrier appears overhead and just sits there. As soon as you see it fire at the engines facing you and then move round to the left to shoot the engines on the other side. Try and get all engines on fire and achievement should pop shortly afterwards.