I would "not" check the box on airline apps because it is specific to "civilian"…I am a military IP and found at least two other sections under work history and professional development/schools to let airlines know I was an IP. Attention to detail on applications is important and you don't want to have to explain padding your app or not following directions when they will have your ARMS/NATOPS reports at the interview and know your an IP/EP. I interviewed at DAL last month and they went line by line on my airline app to check for accuracy and attention to detail. They score your app in advance and will see your IP/EP quails in duty position held and courses attended. Good Luck!