Maybe some of you alredy know this but i still want to post it.
You won't find the purple cockpit when you download the plane, Its caused by a bug that could be useful, here's how to recreate it:
First, you have to be on mobile to recreate this bug since it require you to tap at two place at the same time.
Move the main cockpit and hold it with one finger;
at the same time, tap the cancel button at the down left corner of screen.
the main cockpit will go back to where it was, but under your finger you will find the purple cockpit, which is also marked as a main cockpit!
If you save the purple cockpit in a subassembly, drag one out will turn it into the main cockpit of the plane!