The truth to the passengers should be said, and the problems will be much less.
If you tell the truth, the passengers will go mad.
Example - "Flight N is delayed for technical reasons. At the pre-flight inspection of the air force of the ITS was noticed the bended scapula of the ventilator of the right engine. During 20 minutes, the aircraft technician Kuzyavkin Mithody Kuzmich with the help of a cuvalda and some mother will correct the shoulder. The delay will not affect the time of arrival at the destination airport. Thank you for choosing our company!"