In the triple spool's hot end, the distance between the High Pressure Turbine (HPT) and the Intermediate Pressure Turbine (IPT) also hurts the engine's efficency. This distance is required to locate the disks around an extra pair of shaft bearings.The hot gas flowing at a high subsonic speed in this void requires a lot of cooling air to be introduced which results in a considerable airflow loss that could be used for turning another turbine disk which would mean a lower fuel burn but increase the engine's weight considerably. As well, this void between the two turbine disks allows the hot subsonic airflow to lose some of it's speed and efficency before it hits the IPT blades for more energy extraction. This contributes to the triple spool design having a higher fuel burn than a twin spool disign.