China’s aviation regulator said on Monday that major safety concerns with Boeing’s 737 MAX “have not yet been fully resolved”, in a sign the model is still a long way from returning to service in its largest market. The Civil Aviation Administration of China (CAAC) was working closely with the American planemaker, as well as the US Federal Aviation Administration (FAA), and had conducted comprehensive, in-depth technical reviews of the model, said deputy director Dong Zhiyi at a press conference on Monday. “The cooperation between us is positive and progressing in an orderly manner,” he said. “After the major safety concerns of China get properly addressed, we will carry out certification test flights in a step-by-step and planned way.” China was the first country to ground the 737 MAX planes in the aftermath of two deadly crashes in 2018 and 2019 that killed 346 people. The decisive action, which came amid a heated trade war between the world’s two largest economies, sent a signal that the FAA was no longer beyond reproach. Other countries soon followed China’s lead. The CAAC has been much more cautious than its counterparts in the West in allowing the planes return to service. Australia became the latest nation to lift the flight ban last Friday. The US lifted flight restrictions in November and the European Union declared a modified version of the jet safe to return in January. China will not lift the grounding order until design modifications are recertified, pilots sufficiently trained and clear findings into the crashes released, Dong said. China is Boeing’s largest market and the company is counting on its massive economy for growth in its passenger aircraft business in the future. Boeing 737 MAX: plane’s return to China riddled with uncertainty as tensions with US rage on Boeing said in a report last November that China would become the world’s largest aviation market, with demand for 8,600 new carriers over the next 20 years, up from the estimation of 8,090 in its 2019 forecast. Separately on Monday, Minister of Industry and Information Technology Xiao Yaqing said China’s purchase of 1,000 Boeing planes between 1972 and 2013 showed the country’s huge demand for imports. But he added China was boosting its technological self-reliance by developing its own large passenger jet. China Eastern Airlines announced on Monday it had signed a contract with the state-owned China Commercial Aircraft Company (Comac) to buy five C919 jets , a home-grown alternative to Boeing’s 737 and Airbus’ A320. The first plane is expected to be delivered by the end of 2021.