14 CFR 372.28: Record retention. 1

(a) Every charter operator conducting a charter pursuant to this part shall retain for 2 years after completion of the charter or series of charters true copies of the following documents at its principal or general office in the United States:

(1) All documents which evidence or reflect deposits made by, and refunds made to, each charter participant;

(2) All statements, invoices, bills, and receipts from suppliers or furnishers of goods and services in connection with the charter or series of charters.

(b) Every charter operator shall make the documents listed in this section available upon request by an authorized representative of the Department and shall permit such representative to make such notes and copies thereof as he deems appropriate.