To absolutely no one’s surprise, this seems to be largely a result of the theft of existing designs and technology, and is hardly a Chinese engineering accomplishment.

I guess the good news is that if they copied enough, well enough, maybe it won’t fall out of the sky on a regular basis.

To wit:

(From the Wikipedia article on the C919)

Chinese cyberthreat actor Turbine Panda, linked to the Ministry of State Security’s Jiangsu Bureau, penetrated a number of the C919's foreign components manufacturers including Ametek, Capstone Turbine, GE Aviation, Honeywell, Safran, and others and stole intellectual property and industrial process data with the aim of transitioning component manufacturing to Chinese companies.[26][27][28][29] The report stated that the operations involved both cyber intrusion and theft as well as HUMINT operations, in most cases using a piece of code custom written for this industrial espionage operation.[26][27][28][29]

On October 15, 2018, ten Chinese nationals, including intelligence officials, were indicted by the US for allegedly working with COMAC to allegedly steal the secrets of thirteen foreign aerospace companies working on the C919.[51]

As of 2019, four people have been arrested in the US as a result of investigations into this economic espionage and theft of trade secrets.[29] In November 2022, a federal jury in Cincinnati convicted Yanjun Xu, 42, on counts of conspiracy to commit economic espionage, conspiracy to commit trade secret theft, attempted economic espionage and attempted trade secret theft. The US court found that Xu played a key role in a plot to steal trade secrets from western aerospace firms, for the purpose of helping the C919 commercial airliner program. He was sentenced to 20 years in prison.[30]