GA aircraft use a squat switch to prevent accidental retraction on the ground. Do airliners use a similar system? I've heard some reference to a manual pin, I'd appreciate clarification on that.
$\begingroup$ related: aviation.stackexchange.com/questions/8303/… $\endgroup$– Peter KämpfOct 12, 2015 at 10:31
Most airliners have a protection system for this which is based on Weight-on-Wheels (WoW): sensors which detect load on the wheels (which implies that the aircraft is in contact with ground). For safety reasons this can be bypassed and there's usually a small lever in connection to the gear lever to do this. This image illustrates the 737 gear lever where you can clearly see a "lock override" which fills this functionality (red part)
1$\begingroup$ It is important to note that if you pull the override switch on the ground, you can move the handle, and the gear WILL come up. The WoW sensor only prevents lever movement, not gear retraction. Some planes may be different if course. $\endgroup$– KhantahrFeb 27, 2019 at 23:30