Spirit Airlines, trying to emerge from its second bankruptcy in less than a year, has sold another 20 of its Airbus planes and is bringing flight attendants back from furlough . The sale of the 20 aircraft, most of which are not in service, comes as Spirit is attempting to stabilize after years of financial struggles that have executives fighting to keep the carrier alive . "At this time, natural attrition and voluntary actions are providing flexibility needed to right-size our staffing levels