Leahy tells The Associated Press the pilot reported the plane had hydraulic problems. He says it landed smoothly in Philadelphia on Friday and was met by emergency equipment.
US Airways spokesman Todd Lehmacher says everyone landed safely. He did not immediately know how many passengers were aboard.
Leahy and his fellow passengers are being transferred to another plane for the remainder of the trip to Burlington, which departed Washington's Reagan National Airport just after 10 a.m.
Leahy is third in line to the presidency as president pro tem of the Senate, and had a security team traveling with him.