Mitsubishi Aircraft Corp. said it is sticking to the schedule of handing over its first plane in 2018 after issues with the jet's air conditioning ventilator this weekend grounded the plane from further test flights.

The company is working with United Technologies Corp., the maker of the air conditioning system for the Mitsubishi Regional Jet (MRJ), to fix the problem, company spokesman Yuji Sawamura said by phone from Nagoya.

After two aborted test flights in as many days following the faulty air conditioning system, the nation's first locally built passenger jet was sent back to the hangar for checks and fixes, the latest blow to a key aircraft-building program that has been plagued by delays in its delivery schedule.

Japan's first passenger plane in nearly half a century aims to compete with the dominance of Brazil's Embraer SA and Canada's Bombardier Inc. in the market for planes with fewer than 100 seats. "There is a delay in the U.S. test flight, but we are sure that we can still deliver the plane on time in 2018," Sawamura said.

Mitsubishi Aircraft, a unit of Mitsubishi Heavy Industries Ltd., is trying to break the regional-jet duopoly of Embraer and Bombardier. Mitsubishi had 407 orders for its new aircraft, including options and purchase rights, as of the end of last year. Its two biggest customers were based in the U.S.