A hydraulic system to operate a main landing gear system on an aircraft, the main landing gear system including a left main landing gear actuator and a right main landing gear actuator, the hydraulic system comprising: a first hydraulic power pack (110, 110A) configured to actuate the left main landing gear actuator, the first hydraulic power pack (110, 110A) defining a load interface, a first return interface, and a second return interface, the first hydraulic power pack (110, 110A) including a reservoir, which is fluidly coupled to the first and second return interfaces (114, 116) of the first hydraulic power pack (110, 110A), and a pump configured to draw fluid from the reservoir of the first hydraulic power pack (110, 110A), to pressurize the drawn fluid, and to direct the pressurized fluid to the load interface of the first hydraulic power pack (110, 110A); a second hydraulic power pack (110, 110B) configured to actuate the right main landing gear actuator, the second hydraulic power pack (110, 110B) defining a load interface, a first return interface, and a second return interface, the second hydraulic power pack (110, 110B) including a reservoir, which is fluidly coupled to the first and second return interfaces (114, 116) of the second hydraulic power pack (110, 1110B), and a pump configured to draw fluid from the reservoir of the second hydraulic power pack (110, 110B), to pressurize the drawn fluid, and to direct the pressurized fluid to the load interface of the second hydraulic power (110, 110B); and a backup valve arrangement including a first load bypass interface, a second load bypass interface, a first tank bypass interface, and a second tank bypass interface, the first load bypass interface being fluidly coupled to the load interface of the first hydraulic power pack (110, 110A), the second load bypass interface being fluidly coupled to the load interface of the second hydraulic power pack (110, 110B), the first tank bypass interface being fluidly coupled to the second return interface of the first hydraulic power pack (110, 110A), and the second tank bypass interface being fluidly coupled to the second return interface of the second hydraulic power pack (110, 110B), characterized in that the backup valve arrangement includes a valve spool movable between an open position and a closed position, the valve spool fluidly coupling the first load bypass interface and the second load bypass interface together when in the open position and decoupling the first and second load bypass interfaces when in the closed position, wherein the valve spool is biased to the closed position. a first hydraulic power pack (110, 110A) configured to actuate the left main landing gear actuator, the first hydraulic power pack (110, 110A) defining a load interface, a first return interface, and a second return interface, the first hydraulic power pack (110, 110A) including a reservoir, which is fluidly coupled to the first and second return interfaces (114, 116) of the first hydraulic power pack (110, 110A), and a pump configured to draw fluid from the reservoir of the first hydraulic power pack (110, 110A), to pressurize the drawn fluid, and to direct the pressurized fluid to the load interface of the first hydraulic power pack (110, 110A); a second hydraulic power pack (110, 110B) configured to actuate the right main landing gear actuator, the second hydraulic power pack (110, 110B) defining a load interface, a first return interface, and a second return interface, the second hydraulic power pack (110, 110B) including a reservoir, which is fluidly coupled to the first and second return interfaces (114, 116) of the second hydraulic power pack (110, 1110B), and a pump configured to draw fluid from the reservoir of the second hydraulic power pack (110, 110B), to pressurize the drawn fluid, and to direct the pressurized fluid to the load interface of the second hydraulic power (110, 110B); and a backup valve arrangement including a first load bypass interface, a second load bypass interface, a first tank bypass interface, and a second tank bypass interface, the first load bypass interface being fluidly coupled to the load interface of the first hydraulic power pack (110, 110A), the second load bypass interface being fluidly coupled to the load interface of the second hydraulic power pack (110, 110B), the first tank bypass interface being fluidly coupled to the second return interface of the first hydraulic power pack (110, 110A), and the second tank bypass interface being fluidly coupled to the second return interface of the second hydraulic power pack (110, 110B), characterized in that the backup valve arrangement includes a valve spool movable between an open position and a closed position, the valve spool fluidly coupling the first load bypass interface and the second load bypass interface together when in the open position and decoupling the first and second load bypass interfaces when in the closed position, wherein the valve spool is biased to the closed position.