BEIJING, June 27 (Xinhua) -- China's C919 large passenger plane project is making steady progress, with two planes undergoing flight tests, according to the state-owned Commercial Aircraft Corp. of China (COMAC).

The two C919 planes are undergoing flight tests and preparations in Xi'an and Shanghai, said COMAC.

The C919, China's first self-developed trunk jetliner, conducted its successful maiden flight on May 5, 2017, at Shanghai Pudong International Airport.

The first C919 plane received a series of modifications for its flight tests, including a water balance system modification and overall system calibration. The flight tests are being held in Yanliang, Xi'an of northwest China's Shaanxi Province.

The second C919 has completed multiple tests and modifications for its flight test missions. It is currently undergoing flight tests in Shanghai and will soon fly to the Dongying flight test base in east China's Shandong Province.

To date, the C919 project is on schedule, with flight tests, static tests and ground tests for follow-up planes in order, said COMAC.

The third C919 plane is in its final assembly phase, with its cables and airborne systems currently being installed.

To date, COMAC has received 815 orders for the C919 from 28 customers worldwide.