Mitsubishi Aircraft will roll out Japan's first commercial jet in more than 50 years on Saturday, amid doubts its ambition to sell more than 2,000 of the planes can match reality in the market segment. Developed for $1.9 billion billion by a subsidiary of Mitsubishi Heavy Industries that includes Toyota Corp as a shareholder, the $42 million regional jet, with just under 100 seats, is Japan's second bid at breaking into the commercial aircraft market.