14 CFR § 121.438 - Pilot operating limitations and pairing requirements.
(a) If the second in command has fewer than 100 hours of flight time as second in command in operations under this part in the type airplane being flown, and the pilot in command is not an appropriately qualified check pilot, the pilot in command must make all takeoffs and landings in the following situations:
(2) In any of the following conditions:
(i) The prevailing visibility value in the latest weather report for the airport is at or below 3/4 mile.
(ii) The runway visual range for the runway to be used is at or below 4,000 feet.
(iii) The runway to be used has water, snow, slush or similar conditions that may adversely affect airplane performance.
(iv) The braking action on the runway to be used is reported to be less than “good”.
(v) The crosswind component for the runway to be used is in excess of 15 knots.
(vi) Windshear is reported in the vicinity of the airport.
(vii) Any other condition in which the PIC determines it to be prudent to exercise the PIC's prerogative.
(b) No person may conduct operations under this part unless, for that type airplane, either the pilot in command or the second in command has at least 75 hours of line operating flight time, either as pilot in command or second in command. The Administrator may, upon application by the certificate holder, authorize deviations from the requirements of this paragraph (b) by an appropriate amendment to the operations specifications in any of the following circumstances:
(1) A newly certificated certificate holder does not employ any pilots who meet the minimum requirements of this paragraph.
(2) An existing certificate holder adds to its fleet a type airplane not before proven for use in its operations.
(3) An existing certificate holder establishes a new domicile to which it assigns pilots who will be required to become qualified on the airplanes operated from that domicile.