49 C.F.R. § 800.37
All written comments shall be in English. Unless otherwise specified in a notice requesting comments, comments may not exceed 15 pages in length, but necessary attachments may be appended to the submission without regard to the 15-page limit. Any commenter shall submit as a part of his or her written comments all material he or she considers relevant to any statement of fact made in the comment. Commenters should avoid incorporation by reference. However, if incorporation by reference is necessary, the incorporated material shall be identified with respect to document and page. The NTSB may reject comments if they are frivolous, abusive, or repetitious. The NTSB may also reject comments filed electronically if the commenter does not adhere to the electronic filing instructions at the Federal Docket Management System Web site.
49 C.F.R. §800.37