The platform at the base of the aerofoil forms a continuous annulus ring which, together with cooling-air cavity purge flow prevents hot gas leakage onto the turbine discs. This is a blade with an outer shroud which prevents gas leaking round the blade tip in which case it wouldn't contribute to the force on the aerofoil. Aerofoil individual component of a turbine disc Turbine blade from a Turbo-Union RB199 jet engine.
