Takeoff/go-around switch

Usage in takeoff

Once an aircraft has lined up on the runway, the pilots first increase the engine power to 40–60% N1 (low-pressure compressor RPM) on Boeing aircraft, and 50% N1 on Airbus aircraft. Large jet engines accelerate slowly from idle to approximately 40%, and stabilising the engines prior to applying takeoff power prevents a large thrust asymmetry from causing directional problems if one engine accelerates more quickly. This can also reduce the risk of a compressor stall. Once the engines are confirmed to be stable by the pilot monitoring, the pilots then either press the TO/GA switch, causing the thrust levers to automatically advance themselves to the appropriate power setting (on Boeings), or manually advance the thrust levers to the TO/GA detent (on Airbuses). (In an Airbus aircraft, if de-rated takeoff power is desired, the thrust levers are instead advanced to the FLX/MCT detent.) In all cases, the engine speeds then increase to provide the computed takeoff power. Flight management computers on modern aircraft determine the amount of power needed by the engines in order to reach takeoff speed; a number of factors have to be taken into account, including runway length, wind speed, altitude, temperature, and most importantly the weight of the aircraft. In older aircraft these calculations were performed by the pilots before takeoff. The advantage of having such a system is the ability to reduce wear and tear on the engines by using only as much power as is actually required to ensure the aircraft reaches a safe takeoff speed.

Usage in go-around

The go-around mode is used to fly a go-around from an approach.

If a pilot finds that they are unable to land safely, or deems it necessary to go around for any reason, activating this switch (usually positioned on the throttle levers) will increase the power to go-around thrust. If the switch is pressed again, the engine power will increase to full thrust. Importantly, the TO/GA switch modifies the autopilot and flight director modes, so that they do not continue to follow the previously selected lateral and vertical approach modes and it overrides the auto-throttle mode that was previously controlling the aircraft speed on the approach.

On Airbus aircraft, it does not disengage the autopilot but causes it to stop following the ILS and to perform the go-around maneuver automatically. In an emergency situation, using a TO/GA switch is often the quickest way of increasing thrust to abort a landing.

On some aircraft, the TO/GA switch commands the autopilot to fly a missed approach pattern, if the autopilot is programmed to do so.

References

• Controlling Pilot Error: Automation By Vladimir Risukhin, 2001, , p43-45
• Better Takeoffs & Landings By Michael C. Love, 1995, , page 192
• {{cite web | archive-url=https://web.archive.org/web/20160303222136/http://www.fs.uni-lj.si/mma_bin.php?id=2012082908484829 |url=http://www.fs.uni-lj.si/mma_bin.php?id=2012082908484829

References

1. p. NP.20.31, "Takeoff Procedure", ''Boeing 737-600/-700/-800/-900 Operations Manual''. http://toulouse747.com/wp-content/uploads/2018/12/Boeing-B737-700-800-900-Operations-Manual.pdf
2. "Autothrust (A/THR)", p. 5/18, ''A318/A319/A320/A321 Flight Crew Training Manual.'' https://www.737ng.co.uk/A320%20321%20FCTM%20Flight%20Crew%20Training%20Manual.pdf
3. "Autothrust Operational Aspects", p.2.70.5, ''A330/A340 Flight Crew Training Manual''. http://www.smartcockpit.com/docs/A330-A340_Flight_Crew_Training_Manual_1.pdf {{Webarchive. link. (2021-12-15)
4. (2017-10-20). "TO/GA Party! How Go-Arounds Work".