China's aviation regulator has banned privately owned Okay Airways from buying more aircraft and ordered it to cut down flying hours, in a rare move by the regulator which said the small carrier was overworking its pilots. The Civil Aviation Administration of China (CAAC) said it had made its decision after examining the flight mission documents and crew schedules for 60 pilots and 15 co-pilots from January to May. In a statement, the CAAC's north China division said it found there were 21 instances in which the crew did not take enough time off and another 65 instances of pilots working overtime. Okay Airways executives were not immediately available for comment, but the CAAC statement said the carrier had vowed to rectify the issue and abide by safety rules. Beijing headquartered Okay Airways has a fleet of just 30 aircraft - Boeing B737s and Chinese MA60 planes. Its main hub is Tianjin Binhai International Airport in Tianjin, and it flies mainly domestic routes. It added a few Asian destinations late last year. A surge in demand for air travel in China in recent years has led to a boom in the aviation sector. Last year, more than 831 million people took to the skies, twice as much as in 2008, official statistics show, and Boeing expects China to need more than 6,020 aircraft in the next 20 years, an 8 percent rise over its estimate in 2013.