Low-cost carrier Spirit Airlines said it lost a bid for slots at DCA that are being given up by American Airlines.AA agreed to divest takeoff and landing rights at key US airports under a settlement with the US Justice Department, which had challenged the merger with US Airways."We put in a bid at a price that we thought we could keep our target margin returns in place and we did not win," Spirit chief executive Ben Baldanza said.Baldanza did not say who had won the slots, but said there were no more slots available at the airport.Spirit is also interested in acquiring gates in ORD, LAX and BOS that are also being divested by American Airlines, Baldanza said.AA agreed to divest 52 pairs of takeoff and landing rights, or 104 slots, at DCAThe carrier also agreed to give up gates at airports in BOS, ORD, DAL, LAX and MIA.Southwest Airlines has got 54 slots from American Airlines, while JetBlue Airways has got 24. JetBlue also now owns 16 other slots that were previously under lease from American.