Whilst the grounding of the Boeing 737 MAX is likely to continue for several weeks, the Russian manufacturer Irkut and the Chinese Comac do not waste time. Their respective medium-haul programs MC-21-300 and C919 methodically continue their flight tests. On December 27, the sixth and last prototype of Comac C919 joined the tests, performing a first flight lasted 2 hours and 5 minutes without incident and during which 30 tests were carried out, such as soundproofing and passenger cabin lighting tests. Two days earlier, on December 25, the fourth prototype of the future Russian medium-haul Irkut MC-21-300 joined the test program by making its very first flight lasting 1 hour 40 minutes, again without incident. The fourth Irkut MC-21-300 test aircraft was transferred from the final assembly shop to the plant's flight test division on November 28. In early December, Comac shipped the fifth C919 prototype to Nanchang, southeast China, just over a month after the test aircraft made its first flight.

The Comac C919 "105", the fifth test aircraft, is in Nanchang to undergo a series of tests, especially those of the brakes, fire detection, as well as power supply. The 105 will perform a series of test flights taking off from Nanchang, with extreme temperatures and humidity. This aircraft made its first flight on October 24, 2019. The sixth and last prototype or "106" is dedicated to testing flight controls, stall and extreme temperatures. Two other aircraft are used for static ground tests. Powered by the CFMI Leap-1C, the Comac C919 claims more than 800 firm sales and purchase commitments.

At Irkut’s, the previous and third MC-21-300 test aircraft, MC0004, made its first flight on March 16, 2019. It is equipped with a passenger cabin as well as flight test equipment. This allowed it to be subsequently introduced in Istanbul — and for the first time outside Russia — as part of the Teknofest trade show, which took place from September 17 to 22, 2019.