At the 13th (i.e. the final) compressor stage, air is bled out and used for anti-icing. The amount is controlled by the Pressure Ratio Bleed Control sense signal (PRBC). The "diffuser case" at the aft end of the compressor houses the 13th stage. Its increasing cross-sectional area allows the compressed air to slow down before entering one of the engine's nine burner cans. Again, there are two bosses to extract 13th stage air for anti-icing, de-icing of fuel, and airframe (cabin pressurization) use. Not all the compressed air enters the burner cans at the fuel-ignition point; some bypasses the can completely and cools the first turbine stage, and some is gradually introduced into the burner can's perimeter in such a way that the burning fuel is held near the can's centerline.