A malfunction on U2's private Learjet caused the door of the rear luggage compartment to fall off mid-flight.

Speaking to ABC News, Germout Freitag of the German Federal Bureau of Aircraft Accident Investigation said:

"There can be many reasons for this incident. Either something broke on the door or the door wasn't closed properly. Those are the usual problems that occur."

Though the reason behind the incident is unknown, the passengers on board were not in any serious danger as the luggage compartment is separate from the main cabin, meaning that there was no risk of de-pressurisation.

An investigation will take place, but a report would likely to take about a year to produce.

The band were flying from Dublin to Berlin yesterday to attend the Bambi awards, where they are scheduled to perform tonight.