China Southern Airlines on Friday resumed use of Boeing's single-aisle B737 MAX aircraft for commercial domestic flights, marking the return to the skies of the aircraft model that had been grounded worldwide since March 2019 after it was involved in two deadly crashes.

The first of the four successful flights on Friday was a two-hour afternoon service from Guangzhou, Guangdong province, to Zhengzhou, Henan province, according to VariFlight, a China-based civil aviation data service provider.

Boeing China and China Southern declined comments on the resumption of flights on the B737 MAX in China. The Civil Aviation Administration of China did not offer any comments either.

Two fatal crashes in Indonesia in 2018 and in Ethiopia in 2019, which killed 346 people in all, led to the grounding of the B737 MAX worldwide. Since late 2020, after due corrective process, the aircraft model was allowed to resume flights in many parts of the world. With B737 MAX flights resuming in China on Friday, only Russia remains out of bounds for the aircraft.

In 2022, Boeing landed orders for 774 civil aircraft in all, including those for 561 aircraft from the B737 series and 213 widebody planes. In December, Boeing delivered 69 passenger aircraft to its customers, including 53 B737 MAX planes.

China is Boeing's second-largest market and the largest for its European rival Airbus, according to the two jet makers. The country's 13 domestic carriers boast 97 B737 MAX aircraft in their fleets. China Southern owns 24, Air China 16 and Hainan Airlines 11. Shanghai Airlines, Xiamen Airlines and Shandong Airlines also own some B737 MAX planes.

The CAAC had stipulated that for the B737 MAX flights to resume in China, the aircraft's design modification must be approved for airworthiness, and pilots must be fully and effectively trained again. The investigation conclusions of the two fatal crashes must be clear, and the improvement measures must be effective.

"After China optimized its COVID-19 response measures in December, the domestic air travel market started to rebound strongly. The resumption of flights on the B737 MAX may augur well for the recovery of the market and is expected to provide more capacity for carriers," said Lin Zhijie, an aviation industry analyst and a columnist at Carnoc, a major civil aviation website.