indicator - n. a device that shows a measurement

aviation - n. the business of flying

domestic - adj. of or relating to your own country

income - n. money that is earned from work or investment

principle - n. a basic truth

maintenance - n. the act of keeping equipment in good condition by making repairs, correcting problems, etc.

frequency - n. the number of times that something happens during a particular period

competent - adj. having the necessary ability or skill

coordination - n. the process of organizing people or groups so that they work together properly and well