Northwest Airlines Corp. could end up owning rival Midwest Air Group Inc., which has agreed to a $450 million buyout offer from private equity firm TPG Capital.

Northwest is a passive investor in the deal and may eventually buy Midwest outright, TPG partner Richard P. Schifter said in a conference call Friday.

The equity firm may want to cash out of the deal some day, he said, and Minneapolis-based Northwest could become the sole owner.

Schifter said such a move could be several years away.

Midwest’s decision to sell to TPG came late Thursday night and ended months of back-and-forth with another rival, AirTran Holdings Inc.

Midwest said TPG would pay $17 per share cash, worth about $450 million based on Midwest’s 26.6 million shares outstanding.