It is critical to remember that the CFM56 was certified under the OLD FAR 33 standards that are based on a single 4 lb bird. The new Standard is a single 8 lb bird. Many migratory birds, especially Canada Geese exceed even 8 lbs.
Lastly it is important to understand what the standard for ceritfication of the engine for a single large bird is:
(3) Ingestion of a single large bird tested under the conditions prescribed in this section may not cause the engine to:
(i.) Catch fire;
(ii.) Release hazardous fragments through the engine casing;
(iii.) Generate loads greater than those ultimate loads specified under Sec. 33.23(a); or
(iv.) Lose the ability to be shut down.
It doesn't have to continue to run.....
Once all the FDR data is available for this event, the results of the engine teardown and the bird data is know it will be interesting to see how the information is presented.
Information to date indicates that if the aircraft did hit a flock of geese that the engines exceeded the certification standard.