A gas turbine engine having a rotational axis, comprising: a first shaft connecting a compressor section and a first turbine section, which first shaft is rotatable about the engine rotational axis; and a second shaft connected to a second turbine section, which second shaft is rotatable about the engine rotational axis; wherein the second shaft and the second turbine section together form a module that can be assembled, or disassembled, or both from the engine; and the engine is adapted to permit the second shaft and the second turbine section to selectively move axially forward within the engine to a disassembly position, characterised in that the gas turbine engine further comprises: a first shaft nut having a castellated end surface; and a flange attached to the second shaft having a castellated distal end surface that mates with the castellated end surface of the first shaft nut, wherein in the disassembly position, the castellated end surface of the first shaft nut is engaged with the castellated distal end surface of the flange; and in that the flange attached to the second shaft is L-shaped, with a first leg and a second leg, wherein the second leg includes the castellated distal end surface, wherein the first leg extends radially outwardly from an outer diameter surface of the second shaft, and the second leg extends axially outwardly from the first leg, and a relief channel is disposed between the second leg and the outer diameter surface of the second shaft, further wherein the second leg includes an inner radial surface, and a ramp surface extending between the distal end surface and the inner radial surface. a first shaft connecting a compressor section and a first turbine section, which first shaft is rotatable about the engine rotational axis; and a second shaft connected to a second turbine section, which second shaft is rotatable about the engine rotational axis; wherein the second shaft and the second turbine section together form a module that can be assembled, or disassembled, or both from the engine; and the engine is adapted to permit the second shaft and the second turbine section to selectively move axially forward within the engine to a disassembly position, characterised in that the gas turbine engine further comprises: a first shaft nut having a castellated end surface; and a flange attached to the second shaft having a castellated distal end surface that mates with the castellated end surface of the first shaft nut, wherein in the disassembly position, the castellated end surface of the first shaft nut is engaged with the castellated distal end surface of the flange; and a first shaft nut having a castellated end surface; and a flange attached to the second shaft having a castellated distal end surface that mates with the castellated end surface of the first shaft nut, wherein in the disassembly position, the castellated end surface of the first shaft nut is engaged with the castellated distal end surface of the flange; and in that the flange attached to the second shaft is L-shaped, with a first leg and a second leg, wherein the second leg includes the castellated distal end surface, wherein the first leg extends radially outwardly from an outer diameter surface of the second shaft, and the second leg extends axially outwardly from the first leg, and a relief channel is disposed between the second leg and the outer diameter surface of the second shaft, further wherein the second leg includes an inner radial surface, and a ramp surface extending between the distal end surface and the inner radial surface.