I'm not aware of any terrorist who actually became a commercial pilot, merely those who took a few lessons (1). And I think that's at the upper end of the lengths that terrorists will go to: Past a certain point the low-tech approaches are just way more "bang for the buck", so to speak. And past a certain specialisation of skills, it's way more effective to get that high-paying job and donate to political causes.

1) https://www.sandiegouniontribune.com/lifestyle/people/sdut-g...