Mitsubishi Heavy Industries Ltd. is unlikely to meet the March deadline for delivery of the first test version of a Japan-made stealth fighter to the Defense Ministry, government sources said Tuesday.

The delay was caused by the need to verify a way to restart the aircraft engine if it shut down during flight, the sources said. As a result, they added, the maiden flight will be postponed and the development cost, currently planned at ¥39.2 billion, is likely to increase.

The ministry and Mitsubishi Heavy will hold talks in the near future to set a new delivery deadline, the sources said.

Mitsubishi Heavy declined comment, with an official saying the company is not in a position to disclose development progress.

According to the ministry, development of a full-scale test model began in fiscal 2009 with the participation of several domestic firms in the defense industry.

Assembly of the test model has been completed and it is currently undergoing examinations at a Mitsubishi Heavy plant in Aichi Prefecture.

The prototype fighter jet — 14.2 meters long, 9.1 meters wide and 4.5 meters high — features stealth capabilities through the use of carbon fiber, which absorbs radio waves and makes it difficult for radar to detect the aircraft.

The Defense Ministry aims to develop a domestically made fighter jet, as such aircraft now used by the Air Self-Defense Force are basically produced under license, mainly from Japan’s key ally, the United States.

The ministry apparently aims to play a major role in the joint development of fighter aircraft overseas in the future by gaining technology through developing a domestic model.

Development of fighter jets is also expected to prove beneficial to Japanese manufacturers more widely by enhancing domestic technological prowess.

The ministry has included ¥2.8 billion related to the test model development in its budgetary request for fiscal 2015 starting in April.