Every aircraft has two basic Speed limits, Vmo and Mmo.
(1) Vmo is a structural limit, defined as an Equivalent Airspeed (EAS) which is a direct measurement of the dynamic pressure of the air stream. Aircraft do not have EAS indicators (they should have), and, instead, we refer to CAS indication, which aircraft do have. For a given EAS, CAS increases with increasing Pressure Height, thus, Willy Miller, from the information you've given us, the EAS limit for your aircraft is 284 KEAS.
(2) Mmo is an aerodynamic limit. It is a Mach Number beyond which control problems, and severe loss of thrust from propellers occurs. It has NOTHING to do with the aerodynamic load on your aircraft, but may contribute to undesirable propeller vibration and flexing. High speed propeller aircraft usually do not have Mach Meters, they should have, and the Mmo limit is usually reflected as a decreasing Vmo with increasing Pressure Height.
Mmo is determined at a Mach Number somewhat beyond Mcrit (NOT at Mcrit), where the control problems and/or loss of propeller thrust due to Mcrit exceedance is acceptable. Thus, it is related to Mcrit.
Every component of the aircraft has it's own Mcrit, wings, propellers etc., and Mcrit is usually found at the fastest moving part of the aircraft. For the propeller aircraft, the fastest moving part is the propeller tips, their speed being the VECTOR SUM of their own speed due to rotation and the aircraft forward speed (TAS).
From the information you've given -
I grabbed this snippet from
PPRuNe some time ago, I believe from
Old Smokey, but not sure and apologize to the author in advance.
Cheers, D.L.