Up above a suggestion is made CFM56 -7 have fan blades of a wider chord, different material and perhaps different impact failure modes (speculating due to lack of knowledge, but do understand this may not define how fragile they are).
Perhaps a fair reasoning would be like this. If the -7 fan disk is more durable against impact compared to -5, able to deliver more thrust after an equivalent birdstrike, then
- On your worst luck day with both engines taking hits, you really want to be sitting on an -7 powered aeroplane.
Previously the chances of dual oversize birdstrike were calculated to be acceptably low, the present-day massive traffic rate already started creating recurring events. How long before this will no longer be tolerable? No matter the ratio to departures / ASK would remain the same, at some moment there will be a fatality. And if nothing is done, the intensity will increase which cannot be allowed to happen - for a known problem.
Indeed, keeping the birds away from the intake is the first line of approach.