The C1 and C2 ELEC hydraulic pump selectors control pump operation.
The two center pumps alternate as a primary pump and demand pump. The primary pump operates continuously after the second engine is started. The center demand pump operates under the following conditions:
:on the ground for the first three minutes after the second engine is started, or
from takeoff thrust set until radio altitude exceeds 2000 feet • flaps or slats are in motion, or
during descent from when the gear lever is down and radio altitude is less than 2000 feet until groundspeed is less than 60 knots.
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