Eight years by CAAC Regulation!
And what really matters is the confidence and support of the Chinese people! Within 5 years of commercial production, there will be many tens even over hundreds of C919 flying in the Chinese sky carrying hundreds of thousands passenger within the domestic China. If the aircraft proceed flawlessly in safety record no serious mishap, then such record itself gives the highest testimony on the safety matters, more than any regulator certification!
But by the 10 years of the commercial production run, the COMAC is still far away from fulfilling all the on hand orders as many as 1,005 units (June 2018).
I really don't grasp why some hype the effect of the confidence of foreigners on C919 knowing this situation ... That C919 will have been serving China's own domestic demand for decades before it can deliver any to foreign entity... and many hundreds of the airplane will be flying in the China's airspace ... What one needs further as the safety testimony ???
Unlike other manufacturers of small nations or small market size, COMAC well-being does not rely on the external demand. Just the Chinese own demand will provide ample of orders !!
At least COMAC will have the special leeway of decades-long of commercial services of C919 in domestic China before the foreign concerns ever come into calculation. But when hundreds of the C919 are already in operation and many hundreds of thousands of passengers are moving safely in such a vast and very complex territory as China for so many years, then tell me, what safety concern still remains an issue for any other country with goodwill ???