PHOENIX (AP) -- Authorities say a US Airways flight to Philadelphia had to return to Phoenix's airport and make an emergency landing because of an engine vibration issue.Federal Aviation Administration officials say Flight 714 took off from Phoenix Sky Harbor International Airport about 10 a.m. Thursday and the plane's crew reported feeling the engines vibrating. Authorities say the Boeing 757 circled the airport before it landed without incident around 10:30 a.m. The cause of the engine vibration wasn't immediately known and the plane is being inspected at Sky Harbor. Passengers were booked on other flights. The number of passengers and crew aboard the Phoenix-to-Philadelphia flight wasn't immediately available.