14 CFR § 121.711

Each certificate holder conducting domestic or flag operations must record each en route communication between the certificate holder and its pilots using a communication system as required by § 121.99 of this part.

For purposes of this section the term en route means from the time the aircraft pushes back from the departing gate until the time the aircraft reaches the arrival gate at its destination.

The record required in paragraph (a) of this section must contain at least the following information:

The date and time of the contact;

The flight number;

Aircraft registration number;

Approximate position of the aircraft during the contact;

Call sign; and

Narrative of the contact.

The record required in paragraph (a) of this section must be kept for at least 30 days.