Usually, under the condition that the takeoff lift is stable and the altitude does not drop, if the nose landing gear and the main landing gear cannot be retracted, there is a problem with the hydraulic system or the cable system. If one or two of them can't be recovered, it may be that the landing gear safety pin has not been pulled out (this is common, and it is also the second human error that can't stop, alas). Then you can only return it.

In the landing stage, if the green light doesn't light up after the handle is put down, the solution is to start the Christmas tree (that is, the cockpit light switch is fully open). If the light still doesn't work, it is preliminarily concluded that the light bulb is broken. (Enter the electronic cabin from the cockpit and check whether the front landing gear locking light is on. If it has been locked, it is completely certain that the light bulb is broken and can be landed. If the light is normal, it is a mechanical failure, which is more malicious. If you can't put it down, just put it down.