CHICAGO (Reuters) - U.S. ultra low-cost carrier Frontier Airlines, which is owned by private equity firm Indigo Partners, is planning to resume new pilot hiring this year, a Frontier spokeswoman said on Tuesday. The airline intends to open the pilot application window soon with the aim of re-starting hiring that was frozen during the pandemic by July, provided passenger demand recovers, the spokeswoman said, confirming a report from sources. The current plan is to hire around 100 pilots this year, she said.