Dealing with a Misplaced Needle Spring.
Right hand spring unhooked.
(Left hand spring in correct position.)
The foot joint above belongs to an older model Moeck Rottenburgh tenor. It has two keys that rely on 'needle' springs for their return action. (Nowadays they are often spring wire, usually steel, but really high class instruments can have a gold alloy. Blued steel needles are still available. It is the material I prefer but one has to be very careful to avoid the sharp points.)
How these springs get out of place can be a mystery but usually it is the result of a cleaning cloth getting snagged on the free end of the spring which is then accidentally dragged out of position. In really bad cases the keys must be removed and the spring straightened or replaced. (Push a plain axle out towards the top of the instrument.) This is a more complicated procedure and may well be best done by a technician.