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Capt left, 1st officer or copilot right. On older airlines with a flight engineer, he is behind and is called 2nd officer.

It's the same as a ship. Capt is boss, 1st officer is second in command, 2nd officer if on board is 3rd in command.

Capt always starts the engines and taxis the airplane since most airliners only have a steering tiller on the left, and FO usually handles radios and checklists, FMS programming etc when on the ground. FO, if it's his/her turn to fly, only controls the airplane from the start of the takeoff roll until completion of the landing roll.

On a pairing (sequence of trips over 2 or 3 or 4 days), capt and FO normally alternate on each leg of the trip as pilot flying with the other as pilot monitoring. But as I said, if FO is PF for a particular leg, he/she will still do the radios until the start of the takeoff roll, then takes control of thrust and stick once the capt has lined up, upon which capt looks after comms/FMS/button pushing, until completion of the landing roll, when the FO hands control of the airplane back to the capt and the FO (who only has rudder pedal steering and can't make sharp turns) takes over the radios again.

On an older airliner with a Flight Engineer/Second Officer, that person is type rated on the aircraft as a pilot but never actually flies the plane until he/she moves up to right seat as FO. So in the old 3 crew days a new pilot would be hired as a Flight Engineer in an airline with only 3 crew aircraft and might go several years in the 3rd seat before actually flying the plane, or if upgrading from 2 crew to 3 crew in the same airline.

Up until the 60s you also sometimes had a 4th crew, a Navigator. Don't think there were any Navigators left by 1970.

The title of Captain designates that he(she) has final authority during the flight, and First Officer is assisting. Ultimately, a Captain may make critical decisions regarding the flight. In practice and ideally, the Captain and FO will work collaboratively, and there won't be a need to "pull rank".

The terms Pilot and Co-Pilot are actually rarely used in commercial aviation anymore. Instead, the terms "Pilot Flying" (PF) and "Pilot Monitoring" (PM) are used to designate who has actual hands on the controls, and who is overseeing the flight and providing guidance. The PM also typically handles tasks like radio traffic or setting up the computer (FMS) with proper settings.

A pilot is someone who takes direct part in flying an aircraft by manipulating flight controls.

A captain is a person who can (in the sense of is capable of and legally permitted to) act as a pilot, and who has been hired or promoted by their employer to the rank of captain. They are normally the highest-ranking working employee of the operator aboard the airplane, though exceptions exist. They can typically be recognized by having four gold bars on their shirt shoulders.

A first officer is a person who can (in the sense of is capable of and legally permitted to) act as a pilot, and who has been hired or promoted by their employer to the rank of first officer. It is the rank below captain. They can typically be recognized by having three gold bars on their shirt shoulders.

As already stated, the term co-pilot isn't widely (if at all) used in commercial aviation. Both pilots in the cockpit of a modern airliner are fully qualified pilots, and the terminology has been changed to reflect this fact.

Older airplanes typically had a flight engineer in the cockpit as well; this is a flight crew position, but it is a person that does not directly take part in directing the path of the airplane (it is a non-flying flight crew position). Older yet, they also had a separate position for a navigator, who would tell the pilots where to go. In modern airliners, both of these positions have been replaced by computers.

To answer what you didn't ask, there is another three important terms to know: Pilot Flying, Pilot Monitoring and Pilot In Command.

The Pilot Flying is the pilot that is directly operating the airplane by making control inputs to control the direction in which the airplane is going.

The Pilot Monitoring (or Pilot Not Flying) is the pilot that is keeping an eye on the Pilot Flying, and looking at the instruments, to make sure that the flight is proceeding safely. They will also usually do things at the request of the Pilot Flying. For example, the Pilot Flying may call out for a specific flap setting, or for the landing gear to be raised or lowered, or something similar; the Pilot Monitoring would usually be the one making those airplane configuration changes. The Pilot Monitoring may also be handling radio communications with Air Traffic Control.

Pilots will typically alternate who acts as Pilot Flying and who acts as Pilot Monitoring. This can even change at a moment's notice in the middle of the flight, but there will always be one pilot acting as Pilot Flying and one pilot acting as Pilot Monitoring, and there will always be a clear understanding among all involved who is acting in which role. Accidents have happened when it was not clear in the cockpit who was acting as Pilot Flying and who was Pilot Monitoring, or when the roles became intermingled by one pilot acting in parts of both roles.

The Pilot In Command is the person who is ultimately responsible for the safety of the flight. They can be regarded as the boss in the cockpit, but thanks to the advent of Cockpit Resource Management (CRM), reality is that they are more of a leader than a boss. A good pilot, whether or not they are PIC, will seek the input of their colleagues as much as possible. The PIC will typically be a captain. There is no requirement that at any given time the Pilot In Command is the Pilot Flying. (Some operators may however require in their operational procedures that, say, the PIC, or a captain, is the one performing certain maneuvers, and some aircraft may not be equipped to perform all maneuvers from either seat.)

With these (rough) definitions, we can see that there is no necessary contradiction in something like a flight crew consisting of multiple captains (with a clear understanding of who is Pilot Flying and who is Pilot Monitoring, as well as who is Pilot In Command); or a person who is a captain acting as Pilot Monitoring while another person in the cockpit (or possibly even not in the cockpit) is Pilot In Command, and quite possibly a person who is a first officer acting as Pilot Flying.

In aircraft,they must have a nominated pilot who is the incharge of the aircraft, this pilot is the Captain. A newly qualified airline or private jet pilot is allocated the rank of “First Officer” then later “Senior First Officer” before they take a “Command Course” after which they can become a Captain.

The first officer is the second pilot (also referred to as the co-pilot) of an aircraft. The first officer is second-in-command of the aircraft to the captain, who is the legal commander. In the event of incapacitation of the captain, the first officer will assume command of the aircraft.

1. Job... Pilot flies the airplane, co-pilot helps by doing radios and knobs and switches. Can sit in either seat.
   




2. Rank... Captain is usually the senior person of the two, and is basically the decision-maker. Is seen as a more prestigious and higher-paid job then First Officer. Conventionally sits on the left (but there is no legal requirement for this). Thye Captain is also the 'commander' of the airplane, which is a legal position for "if it goes wrong, the buck stops here".