When are commercial pilots required to carry a valid pilot certificate?

Commercial pilots are required to carry a valid pilot certificate when acting as pilot-in-command because this is a regulatory requirement essential for the legal operation of an aircraft. The pilot-in-command (PIC) is responsible for the safety of the flight and must hold the appropriate certification that verifies their training and qualifications to operate the aircraft being flown.

While certain other scenarios may necessitate having a certificate available, such as for regulatory inspections or validation during training periods, it is the role of the pilot-in-command specifically that mandates the necessity for a valid pilot certificate. The FAA and other aviation authorities impose this requirement to ensure that the individual commanding the aircraft meets the necessary qualifications and is legally authorized to operate it, thus promoting safety in aviation operations.