The company's biggest shareholder, Mitsubishi Heavy Industries last week said delivery of the first M90 would be delayed for at least another year until after March 2021, the sixth delay for the programme and a setback to Japan's commercial jet ambitions.

Mitsubishi Aircraft Chief Development Officer Alex Bellamy said a test plane that had around 960 changes from the original design was due to fly in the coming weeks to prove its airworthiness to regulators.

Some of the changes, such as to crew alerts, were made after two deadly crashes of the Boeing Co 737 MAX that has led to global regulatory scrutiny on pilot responses to emergency situations, he said.

"We have completely redesigned the philosophy of human factors on the flight deck in the last year," Bellamy told Reuters in an interview at the Singapore Airshow.

He said the 90-seat M90 was likely to be a niche aircraft because it was too big to be flown by U.S. regional carriers under their agreement with pilot unions, while the M100 with around 76 seats, due to enter service around 2024, would be the more popular model.

"What it (the M90) does do is it sets that industry foundation," he said. "It really gets us the experience we need operating the product that allows us to mature the M100 and launch the company. It is a milestone on a journey."

Mitsubishi Aircraft's major competitor will be Brazilian manufacturer Embraer SA, which is waiting on final regulator approvals to sell 80% of its commercial aircraft business to Boeing.

Bellamy said there was room in the regional market for both players, noting airline customers were not interested in it becoming a monopoly.

Mitsubishi Aircraft and U.S. regional operator Mesa Airlines Inc in September entered into a memorandum of understanding to begin talks on firm orders for 50 M100s and another 50 purchase rights.

Bellamy said other deals had been signed that would be made public at a later date and hopefully firmed from commitments into orders.

"We have signed a number of commitments with many airlines – a very big number in the hundreds that we haven't publicly disclosed because we still have a lot of work to do before we get there," he said.

By Jamie Freed and Tim Hepher