The captain’s co-pilot, also known in aviation terms as the first officer, is second in command of the aircraft. In the event that anything happens to the captain, the co-pilot will assume command and responsibility of the aircraft.
Control of the aircraft is usually shared equally between both pilots, with one pilot designated to fly the aircraft and the other designated to monitor the aircraft instruments, systems, and respond to all ground communications. Either pilot will input changes to the navigational systems with anticipated, or air traffic control requested updates.
It should be clearly noted that annually, both pilots, the first officer and the captain, must prove their skill and ability under the same training conditions for all flight and emergency procedures.
Generally speaking, both pilots share flying the aircraft by flying every other leg (that is, from takeoff to landing) and logging PIC (Pilot in Command) or SIC (Second in Command) time.
Both captain and co-pilot each hold an Airline Transport Pilot Certificate, also known as an ATP. Airline companies do not hire pilots right out of flight school. Pilots usually start out as co-pilots or flight instructors for charter and regional companies before becoming flight engineers or co-pilots for major airlines.
They can advance to co-pilot and then pilot for a regional airline after obtaining about 2000 hours of flight experience. It usually takes one to five years for a regional co-pilot to advance to a regional captain, and another 10 years to become an airline first officer. All airlines promote to Captain based on seniority.
Most major airlines require four-year degrees. Military pilots generally start flying for the military in their twenties and have already acquired their four-year degree. Their buildup of flight time allows them to apply directly to the major airlines with both experience and education.