BEIJING/SYDNEY, Jan 21 (Reuters) - China Southern Airlines (600029.SS), one of the country"s three biggest carriers, completed a test flight of the Boeing 737 MAX on Friday, as Chinese airlines gear up for the model"s return to service. The Civil Aviation Administration of China (CAAC), the first regulator globally to ground the 737 MAX following two fatal crashes, approved design changes in early December after more than two and a half years. The regulator had expected airlines to resume commercial flights around the beginning of this year. read more A MAX 8 belonging to China Southern, the largest 737 MAX operator in the country, took off from its headquarters city in Guangzhou and touched down three hours and 33 minutes later in the same city, according to aviation data provider Variflight. The plane did not carry any passengers. That followed a Hainan Airlines flight (600221.SS) on Jan. 9 from Taiyuan, where it had parked some of its grounded 737 MAX, to its base city in Haikou. That flight lasted for two hours and 52 minutes, according to tracking websites. Before the MAX was grounded, Boeing was selling a quarter of the planes it built annually to Chinese buyers, its largest customers. CAAC officials had said the planes would need to be modified and pilots would require additional training before the resumption of commercial flights in the country.