Tell that to Sullenberger..

It sounds good in theory and I wish it were true in all cases but facts prove otherwise - foreign object ingestion can and does cause engine failures.

The FAA certification standard for a large bird strike (above 1.85Kg - 4.07lbs) in a turbine engine does not require the engine to continue producing power.

It only requires the damage to be contained within the engine and not result in further damage to the aircraft / airframe.

http://rgl.faa.gov/Regulatory_and_Gu.../ac33.76-1.pdf

Even forgetting about the engines, impact damage anywhere on the airframe can also result in a crash e.g. the Concorde - which was brought down by a 10lb piece of rubber hitting the wing.