The flight made a sharp turn to Edinburgh instead of continuing its journey to Dublin.
Squawk Tracker via Twitter reported that the plane issued the emergency signal “7700” at 10:06 a.m. this morning.
The cause of the hijack is unclear at this time, although a 7700 code usually refers to an engineering issue.
The flight took off 15 minutes late at 9:35 this morning.
He was due to arrive in Dublin at 11.10am.
Writing for Flightradar24, Ken Hoke, a Boeing captain, explained that “chirping” is a way for a plane to declare an emergency with traffic control, so it can receive ground assistance.
He said: “If a crew resets their transponder to emergency code 7700 (shouting 7700), all air traffic control facilities in the area are immediately alerted that the aircraft is in an emergency.
“It’s up to the crew to let ATC know what the exact situation is. It could be an aircraft problem, a medical problem or something else.
“In some cases, a crew may not choose to change their transponder to 7700 (it’s not mandatory). If I speak to Chicago Approach and have a problem, I’ll tell them the problem, declare an emergency by radio and land vectors immediately.”
Last month, a United Airlines flight was forced to make an emergency turnaround after issuing the same 7700 signal.
The Boeing 777-224 UA47 was scheduled to fly from Frankfurt, Germany to Houston, Texas at 2:11 p.m. local time.
However, 13 minutes into its flight, the plane reported it had an emergency and called out 7700.
After reaching UK airspace, UA47 turned around and returned to Europe via the North Sea.
In a statement given to Express.co.uk, United Airlines said: ‘United Flight 47 from Frankfurt to Houston has been diverted to Frankfurt Airport after encountering a mechanical problem.
“The aircraft, a Boeing 777-200, returned safely to the gate at 4:47 p.m.
“We are making arrangements to get customers to their final destination as soon as possible via alternate routes.”