Air enters the front of an engine , where a fan increases the pressure by rotating within a duct . Most of the pressurized air is exhausted through the rear of the engine , where it expands and its velocity increases . Fan disks are large and heavy . The one shown in the photo is over 31 inches ( 1.2 m ) in diameter , and rotates up to 3800 rotations per minute ( RPM ) . Fan disks must withstand the centrifugal force of the attached fan blades . Because of their size and weight , a failed fan disk can severely damage an aircraft , as happened with United Airlines Flight 232 in 1989 . While operating there is increased aerodynamic loading on the fan disk while the fan blade tips are traveling faster than sound.A fan blade weighing 15-lbs can experience upwards of 60 tons of centrifugal force . Fan disks are usually made of a titanium alloy , which is strong , light weight , and resistant to corrosion .
United Airlines Flight 232
United Airlines Flight 232
Fan disk