Abstract: A failure tolerant engine mounting is formed by three links between the engine and its support structure, one of the links being arranged so that in the event of failure of either of the other links it will form a connection between three points on the engine and supporting structure which are symmetrically arranged about a vertical axis through the engines center of gravity.

Abstract: A fan drive system comprising a main drive shaft 13 which drives the fan through a frangible coupling 27 and an auxilliary drive shaft 30 which by-passes the coupling 27. The auxilliary shaft 30 is pre-twisted elastically in the opposite direction to the direction of rotation of the main shaft 13, and is held in the pre-twisted state by the coupling 27. When the coupling 27 disconnects the drive from the main shaft 13, for example when the fan becomes unbalanced and transverse loads exceed a predetermined magnitude, the auxilliary shaft 30 unwinds. Unwinding of the shaft 30 cushions the fan against suddenly applied loads when the coupling 27 breaks and also reduces the loads on the coupling 27 during normal balanced running.

Abstract: The fan rotor (10) of a gas turbine engine is driven by a shaft (16) having a first part (16A) supported in a first radial bearing (17) for rotation about an axis (16C). The shaft (16) further has a second part (16B) secured to the rotor for transmitting torque thereto. The second part (16B) is flexible in bending to allow radial displacement of the rotor (10) relative to the bearing (17). Normally, the rotor (10) is supported against said displacement by a second radial bearing (23). If, due to damage, a given dynamic imbalance on the rotor (10) is exceeded, the resulting unbalanced force (F) transversely to the axis (16C) shears the pins (21C) of a coupling (21) provided between the rotor and the second bearing (23). This then permits the rotor (10) to move eccentrically with respect to the axis (16C) by virtue of the resilience of the shaft portion (16B) thereby cushioning the bearing (17) against the force (F).