The 'Ground Gripper' needed the boost at high wts & above 18c.
(Lucky the Earth is a spheroid, otherwise the Gripper would never get airborne- CFU 27c 67 pax wait 'til 1900lt for temp to moderate, even then a tech stop in NCE. I know I was on it as our Vomet AOG in CFU & me on @ 0630 next day)