"During a routine inspection by BAZL (Bundesamtes für Zivilluftfahrt) we discovered that the airline was a danger to aviation security," said Celestine Perissinotto, a spokeswoman for the Swiss Federal Office for Civil Aviation.
The arguments most commonly set out now show that it was simply a loss of power. One of the 2 Flash Air 737's recently made an emergency landing at ATH with an exploded engine. Dunno whether it was the same.