DEBT LOAD: Pinnacle Airlines Corp., a regional carrier that flies under contract for Delta, United, Continental and US Airways, filed for bankruptcy protection to deal with its mounting debt.

MODEL DIDN'T FLY: The Memphis, Tenn.-based airline said its current business model isn't sustainable. It tried to combine operating subsidiaries to recover from lost business after major airlines cut back on flying. Pinnacle lists $1.42 billion in debt and $1.54 billion in assets.

COLGAN CRASH: Pinnacle's Colgan Air subsidiary operated a plane that crashed near Buffalo, N.Y., in 2009, killing 50 people. That flight was for Continental Connection.

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