A key part of the main landing gear of a civil aircraft is its locking mechanism that holds the gear in the deployed or downlocked state. The locking is driven by a spring mechanism and its release by the unlock actuator. This paper considers this mechanism in terms of its stability and the locking and unlocking forces required for downlocking. Using numerical continuation to solve these equations, the effect of the unlock force on the main landing gear retraction cycle was analyzed. The variation of a fold bifurcation point, which indicates the transition between the locked state and the unlocked state, gives further insight into the required unlock force that governs the sizing of the unlock actuator. Moreover, some important information, such as the critical position for the lock links’ stops, the unlock position, and the unlock force, is discussed using the bifurcation diagrams for the main landing gear retraction/extension cycle. Then, the effect of three key geometry parameters of the locking spring (the spring stiffness, unstrained spring length, and spring attachment point) on the critical over-center angle and the unlock force are investigated. Finally, an optimization of the critical unlock force is carried out with a constraint on the initial over-center angle.