14 CFR §119.61

1. (a)An Air Carrier Certificate or Operating Certificate issued under this part is effective until—
   1. (1)The certificate holder surrenders it to the Administrator; or
   2. (2)The Administrator suspends, revokes, or otherwise terminates the certificate.
2. (b)Operations specifications issued under this part, part 121, or part 135 of this chapter are effective unless—
   1. (1)The Administrator suspends, revokes, or otherwise terminates the certificate;
   2. (2)The operations specifications are amended as provided in § 119.51;
   3. (3)The certificate holder does not conduct a kind of operation for more than the time specified in § 119.63 and fails to follow the procedures of § 119.63 upon resuming that kind of operation; or
   4. (4)The Administrator suspends or revokes the operations specifications for a kind of operation.
3. (c)Within 30 days after a certificate holder terminates operations under part 135 of this chapter, the operating certificate and operations specifications must be surrendered by the certificate holder to the responsible Flight Standards office.