14 CFR §23.2245

1. (a)The airplane must be free from flutter, control reversal, and divergence—
   1. (1)At all speeds within and sufficiently beyond the structural design envelope;
   2. (2)For any configuration and condition of operation;
   3. (3)Accounting for critical degrees of freedom; and
   4. (4)Accounting for any critical failures or malfunctions.
2. (b)The applicant must establish tolerances for all quantities that affect flutter.