MIAMI — After a two-and-a-half-month hiatus, Mitsubishi Aircraft Corporation resumed today the flight test campaign for its long-awaited Regional Jet (MRJ) program.

In a press statement, the manufacturer reported that upgrades, which were not disclosed, were implemented in the Flight Test Aircraft 1 (FTA-1) (JA21MJ / MSN 10001), and were tested in a 90-minute flight off Japan’s Pacific coast.

Today’s test flight was the fourth for the MRJ since its maiden flight that took place last November 11. After gathering the data from the first three flights (the last conducted on November 27), together with the results of the static tests, it was determined that the MRJ required a strengthening of the airframe and a software update.

Last December, Mitsubishi Aircraft Corporation announced another delay, the fourth in the program, with deliveries now scheduled for the second quarter of 2018.

The airframer now plans to continue its flight test campaign in Japan, ahead of the test flights to be conducted in the United States from the fourth quarter of this year. The U.S. campaign will take place at AeroTEC’s Moses Lake Test Center at Grant County International Airport in Washington state.

In total, the flight test campaign is estimated to take 2,500 hours and a will boast a dedicated fleet of five test aircraft.