Further increases in pressure ratio, demanded by government procurement agencies and commercial airlines for long-range aircraft, caused a bigger mismatch of flow areas/density changes and blade angles. Two approaches were followed: slowing the blade speeds at the front of the compressor by splitting it into two separately rotating parts(spools) or making stators variable on the first few stages as well as the inlet vanes. A disadvantage is significant mechanical complexity as each stator blade has to be independently rotated to the desired angles. Two spools need more bearings and turned out to be heavier.