14 CFR § 121.697

The pilot in command of an airplane shall carry in the airplane to its destination the original or a signed copy of the—

Load manifest;

Flight release;

Airworthiness release;

Pilot route certification; and

Flight plan.

If a flight originates at the certificate holder's principal base of operations, it shall retain at that base a signed copy of each document listed in paragraph (a) of this section.

Except as provided in paragraph (d) of this section, if a flight originates at a place other than the certificate holder's principal base of operations, the pilot in command (or another person not aboard the airplane who is authorized by the certificate holder) shall, before or immediately after departure of the flight, mail signed copies of the documents listed in paragraph (a) of this section, to the principal base of operations.

If a flight originates at a place other than the certificate holder's principal base of operations, and there is at that place a person to manage the flight departure for the certificate holder who does not himself or herself depart on the airplane, signed copies of the documents listed in paragraph (a) of this section may be retained at that place for not more than 30 days before being sent to the certificate holder's principal base of operations. However, the documents for a particular flight need not be further retained at that place or be sent to the principal base of operations, if the originals or other copies of them have been previously returned to the principal base of operations.

The certificate holder conducting supplemental operations shall:

Identify in its operations manual the person having custody of the copies of documents retained in accordance with paragraph (d) of this section; and

Retain at its principal base of operations either an original or a copy of the records required by this section for at least three months.