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Origin of the term 
The term arises from the traditional use of traffic patterns at airfields. A landing aircraft will first join the circuit pattern and prepare for landing in an orderly fashion. If for some reason the pilot decides not to land, he can simply fly back up to circuit height, and complete another circuit. The term go-around is still used even for modern airliners, though they may not use traditional circuit patterns for landing. If the aircraft already has its wheels on ground when the maneuver is initiated, then it is called a balked landing.
Reasons for going around 
Initiation of a go-around procedure may be either ordered by air traffic control (normally the local or 'tower' controller in a controlled field) or decided by the pilot in command of the aircraft.
At a towered field, the local controller may instruct the pilot to go around if there is an unsafe condition such as an aircraft, vehicle, or object on the runway. The pilot in command may decide to go around at any time, for example, if the aircraft is not lined up or configured properly for a safe landing; an aircraft, vehicle or other object has not cleared the runway; no landing clearance was received (at a towered field); the landing gear is not properly extended; a dangerous meteorological condition is experienced on final approach (e.g., poor visibility, excessive cross-winds, windshear, etc.); excessive energy (too high or too fast); or any other unsafe condition is detected. In naval aviation, the term wave-off is used instead of go-around. A pilot always initiates a wave-off by applying full thrust when touching down on an aircraft carrier as a fail-safe measure. That way, if his plane's tailhook fails to catch any of the arrestor cables (known as a (deck) "bolter") the aircraft can climb again. If the tailhook catches a cable the aircraft will stop in short order regardless. Conversely if wave-off were not initiated and the aircraft were not arrested, it would not have enough power and/or runway to fly off the carrier.
A go-around does not in itself constitute any sort of emergency (although it could be in response to an emergency). A properly executed go-around is a routine, safe, and well-practiced maneuver.
Many airlines and aircraft operators state a list of conditions that must be satisfied so that a safe landing can be carried out. If one or more of these conditions cannot be satisfied then a go-around should be considered in some cases and must be carried out in others. This list is usually written in the operations manual which has to be approved by the relevant aviation authority (CAA in the UK, FAA in the United States). The operator's list of conditions is not exhaustive; pilots use their individual judgment outside of this scope.
The go-around procedure 
When the pilot is instructed or decides to go around, the pilot applies full power to the engine(s), adopts an appropriate climb attitude and airspeed, raises the landing gear, retracts the flaps as necessary, follows the instructions of the control tower (at a towered field), and typically climbs into the traffic pattern for another circuit if required.
Many modern aircraft, such as the Boeing and Airbus series, use fly-by-wire systems with go-around modes that automatically set maximum available power and pitch the aircraft for best performance, using a TO GA button.
On other aircraft, the pilot configures manually for a go-around. In a typical small aircraft, such as those found in general aviation, this might involve:
- Applying full power (discontinuing carburetor heat if it is on) and setting fuel mixture and propeller pitch if applicable.
- Adopting an appropriate climb attitude and airspeed.
- Retracting one stage of flaps if necessary.
- Checking for a positive rate of climb.
- Raising the landing gear if the aircraft has retractable gear.
- Positioning to the deadside of the runway.
- Retracting the flaps fully when the aircraft achieves a certain safe airspeed and altitude.
- Climbing to pattern altitude.
- Advising control tower and/or other traffic by radio about the go-around.
This is remembered by the mnemonic "5 Cs": Cram it, Climb it, Clean it up, Cool it, and Call it!, or sometimes the "5 Ups": Power Up, Nose Up, Gear Up, Flaps Up, Speak Up.
Flights conducted under instrument flight rules, including all airline traffic, refer to "executing the missed approach" rather than a (VFR) "go-around". The initial steps are the same, but the pilot then follows a pre-defined navigational "missed approach" sequence, published on the approach chart, instead of entering a circuit or pattern. Absent further instructions from ATC, a missed approach sequence directs an aircraft around traffic patterns and terrain into a safe place to begin a holding pattern.
See also 
- avweb.com article (needs registration)