Every airliner has more seats in its flight deck than are needed for just two Pilots . Airliners have flying seats; each sits in front of various instruments and controls. They also have "jumpseats" placed behind the flying seats.
Jumpseats don't have controls, but they are equipped with functionality that helps whoever is occupying them stay in the loop as a flight crew member. Here's an explanation of jumpseats' use in the US aviation market. Jumpseats & their functions The minimum number of jumpseats allowed on a plane for airline operations is one.
Therefore, every plane has at least three seats on the flight deck. The predominant (and legal) reason every airliner must have a jumpseat is to allow an observer to occupy the flight deck during a checking event. Captains need to be observed by the Federal Aviation Administration when finishing their initial training and annually thereafter by company check pilots .
Likewise, first officers are subject to spot checks by company standards pilots at some airlines. Additionally, airlines occasionally require a validation pilot to ride the jumpseat when a pilot is new to an airport or operational theater. For instance, pilots might need an observer on their first trip to Bogotá or Aspen to watch the operation and provide insights.
One further "official" justification for the jumpseat's presence is to allow company or union auditors to have an observational seat. Airlines' standard practice is to randomly place LOSA observers (Li.