The US secretary of transportation, Sean Duffy, has announced a series of measures to help Spirit Airlines passengers following the low-cost airline’s collapse early on Saturday after running out of cash and the failure of rescue talks with the Trump administration. Duffy said that larger US airlines, including United, Delta, JetBlue and Southwest, had agreed to cap ticket prices specifically for Spirit customers who need to rebook canceled flights, subject to a Spirit flight confirmation number and proof of payment. American Airlines and Delta Air Lines would also offer reduced fares on high-