The 737-400F was a type of 737-400 designed to carry cargo. It was not made by Boeing, though. Airlines turned 737-400s into cargo aircraft by themselves. Alaska Airlines was the first to change one of their 737-400s to a 737-400F. It could carry 10 pallets. Alaska Airlines also changed five more 737-400s to carry half passengers and half cargo. These 737-400 aircraft are now being used. The 737-400 has been replaced by the 737-800.