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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
