FARNBOROUGH-U.S. regional operator SkyWest and Mitsubishi Aircraft Corp. have reached an agreement in principle for 100 Mitsubishi Regional Jets (MRJs), and expect a definitive agreement in the coming weeks.

The conditional order is an important boost for Mitsubishi, which in April announced a one-year program delay for the MRJ, pushing entry into service of the initial MRJ90 variant to mid-2015.

If SkyWest confirms its commitment, the MRJ’s backlog will more than double. Mitsubishi has firm orders from All Nippon Airways for 25 aircraft and 50 more from Trans States Holdings, another U.S. regional operator.

Hong Kong lessor ANI Group Holdings also has ordered five MRJs.

SkyWest’s MRJs are scheduled to arrive between 2017 and 2020, although the company, which owns SkyWest Airlines and ExpressJet, will not say which variant it plans to order or how it will allocate the aircraft within its operation.

A Mitsubishi executive, speaking at the Farnborough air show after the SkyWest announcement, also notes that with an expected relaxation of U.S. scope clauses, the company could find more sales opportunities in the world’s largest regional jet market.

President Hideo Egawa during the air show also noted that the program delay was a result of technical studies, which took longer than expected, and issues with component production at Mitsubishi Heavy Industries.

Final assembly of the first prototype is now due to start in early 2013. The MRJ90 is expected to enter service first, followed by the shorter MRJ70. Egawa says Mitsubishi will make a decision on developing a stretched MRJ100X after the MRJ90 has achieved its first flight.

Rick Leach, president of launch customer Trans States Holdings, on Tuesday reaffirmed his commitment to the MRJ in spite of the delay.