The possibility of a rotor part fracturing, especially rotor disks and blades, must not be ignored. Fragments of fractured rotor blades must be contained inside the engine, which can be done by armoring the casing for this purpose. It is impracticable to design for containment of a failed rotor disk due to its mass and energy coupled with the stringent weight limitations on aircraft. Therefore, fragments of rotor disks (Fig. "Rotor failures risk tree"). For this reason, the frequency of rotor disk fractures must be kept considerably lower than that of rotor blade fractures. Thus, if a flaw or defect is found that could potentially result in a fractured rotor disk, this must be confronted with more serious immediate measures than with potential rotor blade failures.