Up-and-coming rivals include Japan’s Mitsubishi Heavy Industries (7011.T), Russia’s Sukhoi (UNAC.MM) and even China’s COMAC, threatening to drive down prices in coming years.

Bombardier virtually invented the regional-jet segment when its CRJ100 entered service in 1992. Embraer broke into the space with its ERJ145 in 1996.

In 2001, Bombardier began offering stretched versions of its regional jets with 70 to 90 seats. Embraer quickly raised the stakes with a new design, including expanded headroom and cargo space, for its E-Jet family seating 70 to 120 passengers.

E-Jets have outsold CRJs since they were introduced eight years ago. By 2012, Embraer controlled just over 50 percent of the regional aircraft market, including turboprop planes, according to the Teal Group aerospace consultancy.

Bombardier’s market share fell below 30 percent, from 72 percent in 2003.

Embraer’s 2011 announcement of a planned overhaul of its E-Jets will put more pressure on Bombardier, eroding the efficiency advantages it touts for the CRJ, which is unlikely to see another engine upgrade, according to analysts.

DOGFIGHT FOR A SEATING CATEGORY

Airlines are often hesitant to switch fleets from one supplier to another, since additional training and maintenance costs can outweigh savings on the purchase.

Delta and US Airways and their regional flying partners operate more Bombardier CRJs. American and United and their partners use more Embraer jets.