last twenty to fifty percent longer than steel brakes, which  results in reduced maintenance. protrudes with the brakes applied is measured to ascertain if  new linings are required.  NOTE: Other segmented multiple-disc brakes may use  slightly different techniques for pressure plate retraction and  wear indication. Consult the manufacturer’s maintenance  information to ensure wear indicators are read correctly. The only impediment to carbon brakes being used on all  aircraft is the high cost of manufacturing. The price is  expected to lower as technology improves and greater  numbers of aircraft operators enter the market.  The segmented multiple-disc brake has given many years of  reliable service to the aviation industry. It has evolved through  time in an effort to make it lightweight and to dissipate the  frictional heat of braking in a quick, safe manner. The latest  iteration of the multiple-disc brake is the carbon-disc brake. It  is currently found on high performance and air carrier aircraft.  Carbon brakes are so named because carbon fiber materials  are used to construct the brake rotors.  [Figure 13-89] An expander tube brake is a different approach to braking that  is used on aircraft of all sizes produced in the 1930s–1950s. It  is a lightweight, low pressure brake bolted to the axle flange  that fits inside an iron brake drum. A flat, fabric-reinforced  neoprene tube is fitted around the circumference of a wheel- like torque flange. The exposed flat surface of the expander  tube is lined with brake blocks similar to brake lining  material. Two flat frames bolt to the sides of the torque flange.  Tabs on the frames contain the tube and allow evenly spaced  torque bars to be bolted in place across the tube between each  brake block. These prevent circumferential movement of the  tube on the flange.  [Figure 13-90] The expander tube is fitted with a metal nozzle on the inner  surface. Hydraulic fluid under pressure is directed through  this fitting into the inside of the tube when the brakes are  Carbon brakes are approximately forty percent lighter than  conventional brakes. On a large transport category aircraft,  this alone can save several hundred pounds in aircraft weight.  The carbon fiber discs are noticeably thicker than sintered  steel rotors but are extremely light. They are able to withstand  temperatures fifty percent higher than steel component  brakes. The maximum designed operating temperature is  limited by the ability of adjacent components to withstand  the high temperature. Carbon brakes have been shown to  withstand two to three times the heat of a steel brake in non- aircraft applications. Carbon rotors also dissipate heat faster  than steel rotors. A carbon rotor maintains its strength and  dimensions at high temperatures. Moreover, carbon brakes  Expander Tube Brakes Carbon Brakes Figure 13-90.  An expander tube brake assembly. Figure 13-89.  A carbon brake for a Boeing 737.  13-51 Brake block Torque bar Frame Torque bar bolt Brake frame bolt Brake spider Adjuster