(Reuters) – The Federal Aviation Administration has cleared Boeing (NYSE:BA) to begin certification flight testing of its 737 MAX 10, the largest version of its bestselling jet aimed at seizing the top of the narrowbody market.

The FAA granted type inspection authorization for the 737 MAX 10 earlier this week, a milestone that allows FAA pilots to participate in flight testing needed to certify the plane for normal operations, three Boeing executives wrote in a letter to employees.

“This is a significant milestone as we work to get the 737-10, the largest airplane in the 737 MAX family, certified to enter passenger service with operators around the world,” said the letter, which was signed by Mike Fleming, Boeing’s senior vice president for development programs, 737 program head Ed Clark, and testing lead Wayne Tygert.

The 737 MAX 10 is Boeing’s answer to the A321neo made by European rival Airbus, which has dominated the lucrative top of the single-aisle market in battles against Boeing’s MAX 9.

Boeing executives last said in October that its schedule for the MAX 10, which calls for the jet to be certified and the first aircraft delivered in 2024, is still on track.

The MAX 10 has so far logged more than 400 flights and almost 1,000 flight hours during Boeing’s test program.

Boeing’s MAX 7 – the smallest entrant of the 737 MAX family – is still awaiting FAA certification, expected by the end of 2023. First delivery slipped from this year to 2024, the company announced in July.