Staffing shortages, schedule changes and higher fares are adding new frustrations to the weather woes that often lead to travel turbulence in the U.S. during the summertime . Crowds are returning to near prepandemic levels , and flights are just about as full as they were in 2019. The number of people passing through U.S. airports Friday hit the highest level since February 2020. Pilot shortages have checked airlines’ growth ambitions, and carriers aren’t flying as much as they had hoped. Hundreds of regional jets that fly to small cities have been grounded.