The present invention relates to a method for determining a precoding matrix indicator, a user equipment UE, a base station eNB, and a system. The rotor blade includes a root and a hollow airfoil having a cavity defined by suction side wall, a pressure side wall, a leading edge, a trailing edge, a base, and a tip. Mounting structure is provided on the wall panel assembly, and is configured with flexible resilient retainers extending outwardly relative to the side structure, and adapted to frictionally engage the inwardly facing flat walls of the vertical frame members, and hold the wall panel assembly over the existing panel and between the vertical frame members.