Similar questions have been asked ; a partial answer is in 14 CFR part 33-76, stating 16 small birds ( 85 g) must be tolerated . But what other qualification tests are there ; for medium and large birds ? I understand the Rolls Royce RB 211 (?) failed the larger bird test and had to be reworked to replace carbon fiber fan blades with titanium. What is the larger bird test ? Accepting that none will survive a flock of geese or ducks.