The go-around procedure may be initiated either by the air traffic control (normally the local or 'tower' controller in a controlled field) or by the pilot in command of the aircraft.
In a controlled field, the local controller may instruct the pilot to go around if there is an aircraft, vehicle or object on the runway or some other unsafe condition. In both controlled and uncontrolled fields, 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 (in a controlled field); the landing gear is not properly extended; a dangerous meteorological condition is experienced on final approach (e.g., poor visibility, excessive cross-winds, etc.); or some other unsafe condition is detected. In naval aviation, a pilot will always initiate a go-around 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 go-around was not initiated and the aircraft was not arrested, it would not have enough power and/or runway to take-off from the carrier.
A go-around does not in itself constitute any sort of emergency (although it may on rare occasions be in response to an emergency). A properly executed go-around is a routine, safe and well-practiced maneuver. Nevertheless, a go-around may cause passengers to become anxious, and if a second go-around is performed many airline policies advise pilots at that point to divert to another airport, rather than attempt landing a third time.
Flights conducted under instrument flight rules, including all airline traffic, refer to "executing the missed approach" rather than a (VFR) go around. The maneuver itself is the same, but the pilot instead follows a pre-defined navigational "missed approach" sequence, published on the approach chart, instead of entering a circuit or pattern. Absent further instructions from the controller, a missed approach sequence directs an aircraft around traffic patterns and terrain into a safe place to begin a holding pattern.
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 performs the go-around manually. In a typical small aircraft, such as those found in general aviation, this might involve:
This is easily remembered by the mnemonic "5Cs" -- 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.