* Trans States Holdings orders up to 100 regional jets
* Second customer after All Nippon Airways
* Mitsubishi Heavy shares up 3.4 pct vs Nikkei 2.5 pct fall (Recasts headline)
By Yuko Inoue
TOKYO, Oct 2 (Reuters) - A Mitsubishi Heavy Industries (7011.T) unit said on Friday that it had won an order for up to 100 regional jets from a U.S. airline, breathing life into Japan's nascent aircraft industry.
Trans States Holdings (TSH), America's second-biggest independent regional carrier, placed an order for up to 100 jets with Mitsubishi Aircraft, becoming its second customer following All Nippon Airways (ANA) (9202.T) and its first client overseas.
TSH said fuel efficiency and other economic advantages over rivals led the company to choose Mitsubishi's jets.
Mitsubishi said it would deliver the first jet to TSH in 2014. The remaining 99 planes will be delivered in the five to six years after the initial delivery.
The order provides a tailwind for Mitsubishi Heavy, which is chasing Canada's Bombardier Inc (BBDb.TO) and Brazil's Embraer (EMBR3.SA) in its $2 billion project to build Japan's first passenger jet.
It aims to sell 1,000 of its jets over the next 20 to 30 years, but has so far only won one order from ANA for up to 25 of its 70- to 90- seat planes, which analysts have estimated to be priced at 3 billion yen to 4 billion yen ($33 million - $45 million) each.
TSH comprises Trans States Airlines, which operates as US Airways Express for US Airways LCC.N and GoJet Airlines, which operates as United Express for United Airlines UAUA.O.
Trans State Airlines has a 48-plane fleet of 50-seat Embraer ERJ145 jets. GoJet's 15-plane fleet consists of 66-seat Bombardier CRJ700 planes. Together, they run 350 flights a day between 50 cities.
Mitsubishi Heavy said last month that it would delay delivery of its first passenger jet by three months to the first quarter of calendar 2014 as it switches to aluminium wings instead of carbon fibre for better fuel efficiency.
Shares in Mitsubishi Heavy, which hopes to beat its rivals by marketing fuel efficient jets, closed up 3.4 percent against the benchmark Nikkei average's .N225 2.5 percent fall. ($1=89.41 Yen) (Additional reporting by Nobuhiro Kubo, Colin Parrott, Mayumi Negishi; Editing by Joseph Radford)