text: Recovery is sometimes impossible in subsonic aircraft; however, as an aircraft descends into lower, warmer, denser air, control authority (meaning the ability to control the aircraft) may return because drag tends to slow the aircraft while the speed of sound and control authority both increase.
  To prevent Mach stall from progressing, the pilot should keep the airspeed below the type's critical Mach number by reducing thrust, extending air brakes, and if possible, extending the landing gear.