Methods and systems for proactively maintaining Digital Loop Carriers and a telephone system local loop. An access provider network that includes an always-on packet data serving node may be used to communicate over a wireless communication link with a mobile station. Compressed gas may be provided to prevent the formation of separation of a main gas flow through the intake and prevent or remove ice accretion. The apparatus provides clusters of the sensors positioned in correspondence to the vertices of substantially equilateral triangles that are defined by tensile elements connecting the clusters. The plural projection type image display devices that together form the display apparatus can be disposed in such a manner that at most one projection type image display device among the plural projection type image display devices forms a projection region of an original shape of projection on a screen.