Mid turbine frame system for gas turbine engine

A gas turbine engine defining a central axis of rotation, and further defining axial and radial directions in the engine relative to the axis, the engine comprising:

• a gas path defined through the engine for directing combustion gases to pass through a turbine rotor having a central disc mounted to a shaft and airfoils extending radially from the disc, the flow of gas through the gas path in use defining upstream and downstream directions within the engine;
• an interturbine duct extending downstream from the turbine rotor, the interturbine duct defined by inner and outer annular shrouds, the shrouds separated by struts extending radially across the gas path, the struts and shrouds co-operating to provide a passageway through the interturbine duct, the interturbine duct inner shroud having a upstream edge disposed axially downstream of the turbine disc, the upstream edge having a diameter not greater than a diameter of the turbine disc such that, in use during a shaft shear event permitting the turbine disc to move axially rearwardly, the disc will contact the inner shroud the upstream edge;
• a mid turbine frame having an outer mid turbine frame case encircling an annular inner mid turbine frame case, the inner and outer mid turbine frame cases connected by at least three spokes extending radially therebetween, the spokes passing through passageways defined through the interturbine duct, the mid turbine frame inner case having a upstream edge spaced axially downstream of the interturbine duct upstream edge, the spokes axially spaced apart from an inner periphery of the passageways;
• an annular engine case connected to a downstream end of the mid turbine frame outer case, the engine case axially abutting a downstream end portion of the interturbine duct outer shroud substantially about an outer circumference of the interturbine duct outer shroud;
• and
• wherein the mid turbine frame upstream edge and spokes are respectively spaced from the interturbine duct upstream edge and passageway inner periphery an axial distance greater than an expected interturbine duct upstream edge axial deflection during said shaft shear event such that the interturbine duct inner shroud, struts and outer shroud provide a load path for transmitting loads form the turbine disc to the engine case during said shaft shear event.