An air boom spreader comprising: a frame; a boom arm extendible transversely to a direction of travel of the spreader; a container mounted on the frame for containing a solid product to be delivered to an environment around the spreader; a product distribution system in product communication with the container for receiving the product from the container; and, an air system in product communication with the distribution system for receiving the product from the distribution system, the air system comprising an air line mounted on the boom arm, the air line connecting the product distribution system to a product outlet situated on the boom arm to permit passage of the product from the product distribution system to the environment through the product outlet, and a fan assembly comprising at least a fan, the fan in fluid communication with the air line and operable to create air flow in the air line to transport the product from the product distribution system to the product outlet, wherein the product distribution system comprises at least one endless solid product metering assembly, the solid product metering assembly comprising: a first endless conveyor and a second endless conveyor for conveying the product from the container to the air system, the first and second endless conveyors (21, 22) substantially parallel to each other, the first conveyor driven independently of the second conveyor; and, a first shaft, a second shaft and a third shaft, the first shaft parallel to, separated from and driven independently of the second shaft, the second shaft parallel to and separated from the third shaft, the first shaft driving the first conveyor, the second shaft driving the third shaft to drive the second conveyor, and wherein the metering assembly further comprises a first motor for driving the first shaft to drive the first conveyor and a second motor for driving the second shaft to drive the third shaft to drive the second conveyor, wherein first and second motors (23, 24) are situated at a same side of the metering assembly. a frame; a boom arm extendible transversely to a direction of travel of the spreader; a container mounted on the frame for containing a solid product to be delivered to an environment around the spreader; a product distribution system in product communication with the container for receiving the product from the container; and, an air system in product communication with the distribution system for receiving the product from the distribution system, the air system comprising an air line mounted on the boom arm, the air line connecting the product distribution system to a product outlet situated on the boom arm to permit passage of the product from the product distribution system to the environment through the product outlet, and a fan assembly comprising at least a fan, the fan in fluid communication with the air line and operable to create air flow in the air line to transport the product from the product distribution system to the product outlet, wherein the product distribution system comprises at least one endless solid product metering assembly, the solid product metering assembly comprising: a first endless conveyor and a second endless conveyor for conveying the product from the container to the air system, the first and second endless conveyors (21, 22) substantially parallel to each other, the first conveyor driven independently of the second conveyor; and, a first shaft, a second shaft and a third shaft, the first shaft parallel to, separated from and driven independently of the second shaft, the second shaft parallel to and separated from the third shaft, the first shaft driving the first conveyor, the second shaft driving the third shaft to drive the second conveyor, and wherein the metering assembly further comprises a first motor for driving the first shaft to drive the first conveyor and a second motor for driving the second shaft to drive the third shaft to drive the second conveyor, wherein first and second motors (23, 24) are situated at a same side of the metering assembly. a first endless conveyor and a second endless conveyor for conveying the product from the container to the air system, the first and second endless conveyors (21, 22) substantially parallel to each other, the first conveyor driven independently of the second conveyor; and, a first shaft, a second shaft and a third shaft, the first shaft parallel to, separated from and driven independently of the second shaft, the second shaft parallel to and separated from the third shaft, the first shaft driving the first conveyor, the second shaft driving the third shaft to drive the second conveyor, and wherein the metering assembly further comprises a first motor for driving the first shaft to drive the first conveyor and a second motor for driving the second shaft to drive the third shaft to drive the second conveyor, wherein first and second motors (23, 24) are situated at a same side of the metering assembly.