Front frame is made from a high-strength stainless steel casting. Twelve equally spaced radial struts are used between the hub and outer case to provide support for the inner hub. Twelve variable-position bypass valve doors are located on the outer wall for the low pressure compressor discharge bleed.
The front frame contains the engine A-sump, which includes a thrust bearing (1B) and roller bearing (2R) that support the low pressure compressor rotor, and a roller bearing (3R) that support the forward end of the high pressure compressor rotor. Lubrication oil supply and scavenge lines for the A-sump are routed inside the frame struts. The inlet gear box is located in the A-sump with the radial drive shaft extending outward through the strut located at the 6 o’clock position.