Turbine Engines Some high-volume turboprop and turbojet engines are equipped with two-spool or split compressors. When these engines are operated at high altitudes, the a. low-pressure rotor will increase in speed as the compressor load decreases in the lower density air. b. throttle must be retarded to prevent overspeeding of the high-pressure rotor due to the lower density air. c. low-pressure rotor will decrease in speed as the compressor load decreases in the lower density air.