Abstract: Each landing gear of the undercarriage of an aircraft includes an hydraulic cylinder, and the hydraulic cylinders are interconnected through hydraulic restoring devices. The hydraulic restoring devices yieldably urge the pistons in each of the hydraulic cylinders to an equilibrium position, thereby restoring the length of each landing gear to an equilibrium length following a disturbance. In non-level landings, the hydraulically interconnected system causes the landing gear that strikes the ground first to be compressed and the other landing gears to be extended; this absorbs some of the energy of the impact. Extension of the other landing gears tends to limit the extent to which landing energy is converted to angular velocity of the aircraft caused by pivoting of the center of gravity of the aircraft about the first landing gear to contact the ground.