  Necessary and sufficient stability and instability conditions are obtained
for multi-term homogeneous linear fractional differential equations with three
Caputo derivatives and constant coefficients. In both cases,
fractional-order-dependent as well as fractional-order-independent
characterisations of stability and instability properties are obtained, in
terms of the coefficients of the multi-term fractional differential equation.
The theoretical results are exemplified for the particular cases of the Basset
and Bagley-Torvik equations, as well as for a multi-term fractional
differential equation of an inextensible pendulum with fractional damping
terms, and for a fractional harmonic oscillator.
