听力原文：Can I have your attention, please? Passengers waiting for flight GE sixty-four, there's been a gate change. Let me repeat that: Flight GE sixty-four, flying to Charlotte and then on to Miami, is NOT departing from Gate F-twenty-seven. Flight GE sixty-four will depart from Gate B-nine. The departure time has been pushed back from four o'clock to four-fifteen. A shuttle to concourse B will be arriving shortly. We're sorry for the inconvenience, but the plane that is currently here at Gate F-twenty-seven is experiencing mechanical troubles and will not be going anywhere for a while. So we'll be taking off from Gate B-nine instead. Thank you for your patience. What is the purpose of this announcement?