The Air Operator’s Certificate (AOC) is granted to an airline that can launch and stay operational, but it can only be granted once it has the aircraft, staff, safety systems, and financial resources available. This is one of the most common reasons for an airline to lose its AOC. Examples include Estonia's SmartLynx Airlines, Austria's Mali Air, Malta's HiFly, Swedish charter carrier H-Bird, and Houston-based charter carrier Starflite Aviation. British charter airline Pen-Avia also no longer has an active AOC license and is unable to legally run or market flights to passengers. Other airlines that lost their AOCs struggled to make up for the high cost of aviation due to high demand for charter flights.