For context: passenger jets have a positive feedback system that indicates to the pilots whether or not the gear is in the correct position. When they operate the control to raise or lower the gear, there are corresponding indicator lights that confirm whether or not the gear has successfully moved to the commanded position. Part of standard procedure is to lower the gear, and then verify that all of the indicator lights confirm that the gear has successfully moved into the correct position. If they are not working properly, it is apparent from the indicator lights. They will then know that they will have to abort the approach and run troubleshooting checklists for that particular issue.