ALNPY ANA Holdings Inc (PK)

NAGOYA, Japan—The builder of Japan's first commercial jetliner said Thursday that it would delay its delivery to airline customers by about a year, until 2018, in the latest of a series of setbacks for the project.

Mitsubishi Heavy Industries Ltd., a descendant of the company that made the legendary Zero fighter of World War II, said it had identified several areas requiring further investigation since the airliner's first flight in November. Company executives, at a news conference here, cited a need to strengthen the airframe, but declined to elaborate on specific problems or possible solutions.

The Mitsubishi Regional Jet, a 70- to 90-seater designed for short-haul flights, was previously expected to join the fleet of its first customer, ANA Holdings Inc.'s All Nippon Airways, in the second quarter of 2017. Mitsubishi Heavy said it now aimed to deliver the MRJ "approximately one year later," and executives said the timetable could slip further, subject to subsequent reviews.

Analysts say the latest delay could alarm existing customers, who have placed orders or options for more than 400 of the planes, as well as discouraging other potential buyers as the jet competes with new and existing regional jets made by Bombardier Inc. and Embraer SA.

One of the $45 million jet's main selling points has been its next-generation technology, including fuel-efficient new engines from Pratt & Whitney, a division of United Technologies Corp. By delaying delivery, Mitsubishi could lose a first-mover advantage over Embraer, which said it remains on track to deliver the first of its upgraded E2 jets with similar Pratt engines in 2018.

"If the MRJ is going to take some of the regional jet market it is important that it gets ahead" of Embraer, said Ben Moores, aviation analyst at IHS Janes. Embraer couldn't immediately be reached for comment.

Mitsubishi Aircraft Corp., a Mitsubishi Heavy subsidiary that is coordinating the project, said it had conducted three flight tests, finding that the plane performed largely as planned. The company said, however, that as a result of input from U.S. experts it was working to strengthen the airframe and upgrade the system software.

"We are improving the strength in order to enhance safety," said Nobuo Kishi, senior executive vice president of Mitsubishi Aircraft.

"We are recognizing that we lack experience after a 50-year gap," he added, referring to the time that has passed since Mitsubishi joined other Japanese aircraft makers to build the propeller-driven YS-11 airliner.

SkyWest Inc., the largest U.S. regional airline operator by revenue, has as many as 200 of the Mitsubishi jets on order. In advance of Mitsubishi's news conference Thursday, a SkyWest spokeswoman said the company was sticking with its order, but said it was "dependent on flying contracts, scope and aircraft availability."

St. Louis-based Trans States Holdings—which operates flights on behalf of U.S. network airlines and has orders and options on up to 100 Mitsubishi Regional Jets—declined to comment.

ANA said in a statement that while "this latest delay is very disappointing, we remain confident of the benefits the MRJ will bring to the ANA fleet."

When Mitsubishi Heavy began development of the jet in 2008, it had envisioned the plane's entry into commercial service occurring as early as 2013. Since then, there have been at least four major delays.

After the latest of these, "ongoing sales campaigns will become more challenging, with potential customers increasingly nervous about MRJ program execution and certainty of delivery date," said Rob Morris, head of consultancy at Ascend Flightglobal in London.

If customers abandon the project, it would be a big setback for Japan Inc., which has been counting on the plane to signal a Japanese industrial revival. The jet draws on parts from dozens of domestic suppliers, and the government of Prime Minister Shinzo Abe has pledged to support Mitsubishi's efforts to sell it to airlines around the world.

Emperor Akihito said during a news conference marking his 82nd birthday this month that he was "overjoyed" by the MRJ's maiden flight, citing it as one of the notable events of the past year.

While Mitsubishi Heavy and other Japanese companies are major suppliers to Boeing Co. and Airbus Group SE, conceiving and executing a commercial airliner from scratch is vastly more complicated than providing parts for one.

Doug Cameron in Chicago contributed to this article.

Write to Eric Pfanner at eric.pfanner@wsj.com and Chieko Tsuneoka at chieko.Tsuneoka@dowjones.com

(END) Dow Jones Newswires

December 27, 2015 03:45 ET (08:45 GMT)

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