Challenges Abound for New Chief at Beleaguered United Airlines
United Airlines' new chief executive, John W Creighton Jr, will presumably have to move quickly stanch losses estimated at $20 million a day; must also refashion management team that has lost credibility with employees and manage expectations of labor unions that helped topple his predecessor, James E Goodwin; Frederick C Dubinsky, chairman of Air Line Pilots Association unit at United, strongly endorses Creighton but is cool to idea of wage concessions; many analysts think that such concessions are critical to turning United around; photo (M)