Pinnacle Airlines filed for bankruptcy protection on Sunday, indicating that they could no longer maintain the necessary cash flow to operate their business. In large party they blame the fixed capacity purchase agreement penned with Continental and still operated under the United Express brand, with the Saab 340s and Q400s as the planes causing the losses. United temporarily extended the company a life-line, agreeing to increase the payment rates for a two month period. That agreement expired yesterday and the company was no further along in negotiating concessions from ALPA so they're throwing in the towel. The 340s will be removed from service by the end of July and the Q4s by the end of November. It remains to be seen what United will do to replace this capacity, though some ERJ135s have come out of storage. Of course, these are more expensive to operate on a CASM basis but at least the routes will remain in many cases. Also of note, the DL CRJ-900s will be retired in the first half of 2013. More coverage of the Pinnacle bankruptcy filing can be found here or here.