SkyWest Inc. has finalized an order for 100 Mitsubishi Aircraft MRJ regional jets announced in June, adding options for a further 100, and sticking with its original plan to use the firm order for the larger MRJ90 aircraft—at least for now.

The MRJ90 holds 90 seats in a single class, compared with 70 for the MRJ70. That is significant for U.S. regional carriers, such as the SkyWest subsidiaries, which operate the vast majority of their flights for major carriers under their brand names. That is because scope clauses in the major carrier collective bargaining agreements with their pilots limit by aircraft size and number the amount of flying that can be outsourced to regional carriers.

When SkyWest placed its tentative order in June, Kraupp said the carrier would wait to see how scope clauses at its major airline partners and potential future partners take shape before deciding whether to stick with the MRJ90s. If United Airlines pilots approve their tentative contract when the votes are counted on Dec. 15, the new upper limits will have been established for Delta, United and American Airlines at 76 seats. The only major network carrier higher than that is US Airways, at 90, so the picture could change a bit if it merges with American.

Kraupp now says that, either way, the MRJ90 could be a good fit.

“The MRJ90 can be configured to 76 seats to comply with current scope limitations,” Kraupp told Aviation Week on Dec. 13. “Since the aircraft don’t deliver for a few years, we will see where scope clauses migrate to when making final determinations as to which aircraft to take and how many seats.”

Kraupp says SkyWest probably needs to decide by 2015 whether to switch its order to MRJ70 aircraft. As to which airlines SkyWest will be operating the MRJ for, he says only that “we will have an ongoing effort to offer the aircraft to all of the U.S. majors and see what their appetite is.”

As for its order, SkyWest and Mitsubishi say each batch of 100 aircraft is valued at $4.2 billion, presumably referring to catalog prices. Pratt & Whitney PW1200G geared-turbofans will power the MRJ.

In agreeing to unstated rights and obligations, the companies say they will “mutually position themselves for opportunities in the U.S. airline industry.”

The addition of options to the deal underscores SkyWest’s statement this year that that it might want more than 100 MRJs. The problem, however, is that Mitsubishi Aircraft, struggling with development delays, cannot deliver more than the first 100 this decade. If the options are taken up, the aircraft that they cover will be delivered from 2021.

The aircraft in the firm order will be delivered from 2017, as previously stated. The contract takes the MRJ order book to 165 units, almost three years of production at the maximum planned production rate of five units a month—and much longer when the ramp-up after first delivery is taken into account.

Seeking to offset the development delays, Mitsubishi Aircraft is looking for ways to reach full-rate MRJ production faster than its original, unstated schedule, and then to build faster than the planned rate of five a month.

First delivery to initial customer All Nippon Airways is due in late 2015 or early 2016, at least two years later than the target set when the program was launched in 2008. ANA has ordered 15 MRJs, and Trans States Airlines of the U.S. has ordered 50.

SkyWest Inc. owns SkyWest Airlines, based in St. George, Utah, and ExpressJet Airlines, based in Atlanta, Ga. They operate under the brands United Express, Delta Connection, American Eagle and US Airways Express. SkyWest Airlines also operates flights for Alaska Airlines.

Mitsubishi Aircraft is partly owned by Mitsubishi Heavy Industries, the prime contractor for the MRJ fuselage.