WE CLAIM:
1. A planet gear train (200) for an engine casing (226), comprising:
a sun gear (204) rotatable by a shaft (202);
a ring gear (208);
a plurality of planet gears (206) rotatably mounted in a planet carrier (210) and meshing with said sun gear (204) and said ring gear (208); and
a damping system comprising:
a soft mount (212) disposed about said shaft (202) and coupling said planet carrier (210) to said engine casing (226), said soft mount (212) including a flexible inner sleeve (214) and a flexible outer sleeve (216), said flexible inner sleeve (214) and said flexible outer sleeve (216) being fixedly coupled together at respective central portions thereof near said shaft (202); and
a plurality of damping couplers (218) disposed about an outer flange (232) of said planet carrier (210), said plurality of damping couplers (218) flexibly coupling said flexible inner sleeve (214) to said flexible outer sleeve (216).
2. The planet gear train (200) of Claim 1, wherein said plurality of damping couplers (218) each further comprise a central axial spring (306) and an outer radial spring (302, 304).
3. The planet gear train (200) of Claim 2, wherein said central axial spring (306) comprises a structure (310) configured to provide flexible rigidity in an axial direction of rotation of said shaft (202).
4. The planet gear train (200) of Claim 2, wherein said outer radial spring (302, 304) comprises a structure (420, 422) configured to provide flexible rigidity in a radial direction perpendicular to the axial rotation of said shaft (202).

5. The planet gear train (200) of Claim 4, wherein said outer radial
spring (302, 304) comprises:
a coupling ring (302) coupled to the engine casing (226, 320), said coupling ring (302) including slots (330) spaced circumferentially about an inner circumference (326) of said coupling ring (302), each slot (330) comprising a cross-section; and
a spline ring (304) coupled to said planet carrier (210, 318), said spline ring (304) including a plurality of radially extending splines (420, 422) shaped to match the cross section of a respective slot (416, 418), the cross section of each slot (416, 418) including at least one shoulder configured to engage a surface of a respective spline when a relative position between said coupling ring (302) and said spline ring (304) changes by a predetermined amount such that a deflection of at least one of said coupling ring (302) and said spline ring (304) is limited in the radial and circumferential directions.
6. The planet gear train (200) of Claim 5, wherein said spline ring (304) further comprises a cylindrical interior (326), and wherein said central axial spring (306) is disposed within the cylindrical interior (326).
7. The planet gear train (200) of Claim 6, wherein said central axial spring (306) is fixedly coupled to said outer flange (318) of said planet carrier (210).
8. The planet gear train (200) of Claim 6, wherein said coupling ring (302) is fixedly coupled to one of the engine casing (226, 320) and said flexible outer sleeve (216).
9. The planet gear train (200) of Claim 5, further comprising a supply (220) of damping agent to each slot (330, 414), said supply of damping agent configured to resist a movement of said spline (420, 422) in each slot (414) such

that a vibratory motion between said coupling ring (302) and said spline ring (304) is damped.
10. The planet gear train (200) of Claim 9, wherein said damping agent is a fluid.