Takeoff/Go-around switch
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A Takeoff/Go-around switch (TO/GA) is a switch on the autothrottle of modern large aircraft, with two modes: takeoff (TO) and go-around (GA). The mode is dependent on the phase of flight; usually, on approach to land, the autopilot will be set to approach mode, therefore if the TO/GA switch is pressed it will activate the go-around mode of the autothrottle; conversely, when take-off is set on the autopilot, the switch activates take off mode of the autothrottle. On Boeing aircraft TO/GA modes are selected by a separate switch near the throttle levers, but on Airbus aircraft it is activated by pushing the thrust levers fully forward to the TO/GA detent.
Contents
Takeoff
Once an aircraft has lined up, the pilots increase the engine power. The level reached is 40–60% RPM of low pressure turbine on Boeings, and 50% on Airbuses. This is done to prevent flame-out on takeoff due to compressor stall. The pilots then press the TO/GA switch, by pushing the thrust levers to TO/GA on Boeings or to TO/GA or FLEX detent on Airbuses, and 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 during approach. If a pilot finds that he or she is unable to land safely, activating this switch (usually positioned on the back of the throttle levers)will increase the power to go-around thrust. Most importantly, the TO/GA switch modifies the autopilot mode, so it does not follow the ILS glideslope anymore and it overrides any autothrottle mode which would keep the aircraft in landing configuration. On Airbus aircraft it does not disengage the autopilot, but causes it to stop following the ILS and perform go-around manoeuvre automatically. In an emergency situation, using a TO/GA switch is often the quickest way of increasing thrust to abort a landing. On Airbus planes pushing throttles to TO/GA detent does all regarding flight path and speed.
Some aircraft make the TO/GA switch to command the autopilot to fly a missed approach pattern, if the autopilot is programmed to do so.
See also
- China Airlines Flight 140, crash caused by inadvertent activation of the TO/GA switch
