<p>A turbine blade tip plenum (100) has means for preferentially directing or diverting cooling air from a cooling passageway network to cool areas subject to extreme heat. In one embodiment, the leading end (144) of a cover plate (50) may partially obscure a passage (110) into the plenum (100) so as to preferentially direct cooling air to the pressure side (64) of the blade (40). The rear of the plate (50) may also be arranged to direct air preferentially to the pressure side (64).</p>