Takeoff/Go-around switches

Takeoff/Go-around switches (TO/GA) are switches activated on the autothrottle of an autopilot of a modern aircraft. It has two modes, takeoff (TO) and go around (GA).The switch is the same for both takeoff and go around modes, the autopilot & throttle programming knows what stage the flight is in by how the autopilot is set. Usually on approach to land the autopilot will be set to approach mode on the autopilot therefore if the TO/GA switch is pressed it will activate the go around mode.

Takeoff

Once an aircraft has lined up, the pilots increase the engines to approximately 50% power (this is done to ensure that an uneven application of power does not happen when the take off starts) and then press the TO/GA switch, the engines then increase to their computed take off power. Modern aircraft flight management computers will determine the power needed by the engines to take off based on a number of factors such as runway length, wind speed, temperature, and most importantly the weight of the aircraft. In older aircraft these calculations were performed by the pilots before a takeoff. The advantage of having such a system is the ability to reduce wear and tear on the engines by only using as much power as is actually required to ensure the aircraft reaches a safe take off speed.

Go around

The go around setting is used when a landing is taking place. If a pilot finds that they are unable to land, activating this switch will increase the power to go-around thrust, the aircraft will command an increase in pitch to cause the aircraft to climb, and if the autopilot is engaged, it will route the aircraft into the designated missed approach pattern. The GA switch can be used even after touchdown if reverse thrust has not been selected.

References

* [http://books.google.com/books?id=jHTjCdqdLNQC&pg=PA45&lpg=PA45&dq=takeoff+go+around&source=web&ots=x1PdcIq1eQ&sig=f_i40zTbE0OffnFZ71rDIV4DbC4&hl=en Controlling Pilot Error: Automation By Vladimir Risukhin]
* [http://books.google.com/books?id=p9XT6aHBrGAC&pg=PA192&lpg=PA192&dq=takeoff+go+around&source=web&ots=ekPPPsDpHt&sig=RoNG3iapMdhlGtHD0zI4jZRtxy0&hl=en Better Takeoffs & Landings By Michael C. Love]