This issue has gained new urgency beyond just Spirit. United Continental Holdings Inc. is working to smooth reliability shortfalls that triggered customer defections dating to its 2010 merger, and American Airlines Group Inc. is melding two mainline fleets and schedules while fixing weaknesses in its regional unit. Both labor under the shadow of a widely praised operation at Delta Air Lines Inc., which has begun aggressively marketing its performance and commanding higher fares because of it. At Miramar, Fla.-based Spirit, the lack of emphasis on service, in part, spurred the board to bring in Fornaro, 63. With the airline's cost mandates, the new CEO decided he had to prioritize. Delays tend to have an outsize impact on Spirit because of how its network is configured, with some cities seeing only one flight per day and others a few per week. Stranding passengers and trying to get an 87-jet fleet on track following, say, a big winter storm, can quickly snowball into an expensive mess.