AOG or Aircraft On Ground is a term in aviation maintenance indicating that a problem is serious enough to prevent an aircraft from flying. [1] This can involve problems as simple as a light bulb being out, flat tire, or as complex as a damaged engine. Boeing estimates that a 1-2 hour AOG situation will cost an airline from $10,000 to $20,000 and possibly even as high as $150,000 per hour depending on the type of aircraft and route flown. In the corporate/ private jet flight market, Advanced AOG and Avionics estimates more than 1,000 AOG maintenance events occur everyday in North America, making companies like their own, which specialize AOG maintenance events, an instrumental part of a successful flight department. [2] [3]