14 CFR § 135.100

No certificate holder shall require, nor may any flight crewmember perform, any duties during a critical phase of flight except those duties required for the safe operation of the aircraft. Duties such as company required calls made for such nonsafety related purposes as ordering galley supplies and confirming passenger connections, announcements made to passengers promoting the air carrier or pointing out sights of interest, and filling out company payroll and related records are not required for the safe operation of the aircraft.

No flight crewmember may engage in, nor may any pilot in command permit, any activity during a critical phase of flight which could distract any flight crewmember from the performance of his or her duties or which could interfere in any way with the proper conduct of those duties. Activities such as eating meals, engaging in nonessential conversations within the cockpit and nonessential communications between the cabin and cockpit crews, and reading publications not related to the proper conduct of the flight are not required for the safe operation of the aircraft.

For the purposes of this section, critical phases of flight includes all ground operations involving taxi, takeoff and landing, and all other flight operations conducted below 10,000 feet, except cruise flight.

For the purposes of this section, taxi is defined as movement of an aircraft under its own power on the surface of an airport and includes hover taxi which is movement of a helicopter or any vertical takeoff and landing aircraft conducted above the surface and in ground effect at airspeeds less than approximately 20 knots, and air taxi which is movement of a helicopter or any vertical takeoff and landing aircraft conducted above the surface but normally not above 100 feet AGL.