exhaust gases are directed into the augmentor bellmouths.  The augmentors are designed to produce a venturi effect to  draw an increased airflow over the engine to augment engine  cooling. An augmentor vane is located in each tailpipe. When  the vane is fully closed, the cross-sectional area of the tailpipe  is reduced by approximately 45 percent. The augmentor  vanes are operated by an electrical actuator, and indicators  adjacent to the augmentor vane switches in the cockpit  show vane positions. The vanes may be moved toward the  “closed” position to decrease the velocity of flow through  the augmentor to raise the engine temperature. This system is  only used with older aircraft that generally use radial engines. Any exhaust system failure should be regarded as a severe  hazard. Depending on the location and type of failure,  an exhaust system failure can result in carbon monoxide  poisoning of crew and passengers, partial or complete loss  of engine power, or an aircraft fire. Cracks in components,  leaking gaskets, or complete failure can cause serious  problems in flight. Often, these failures can be detected  before complete failure. Black soot around an exhaust gasket  shows the gasket has failed. The exhaust system should be  inspected very thoroughly.  While the type and location of exhaust system components  vary somewhat with the type of aircraft, the inspection  requirements for most reciprocating engine exhaust systems  are very similar. The following paragraphs include a  discussion of the most common exhaust system inspection  items and procedures for all reciprocating engines.  Figure 3-42  shows the primary inspection areas of three  types of exhaust systems. Some radial engines are equipped with a combination  exhaus manifold and augmentor assembly. On a typical  18-cylinder engine, two exhaust  assemblies and two  augmentor assemblies are used. Each manifold assembly  collects exhaust gases from nine cylinders and discharges the  gases into the forward end of the  augmentor assembly. The  When performing maintenance on exhaust systems, never use  galvanized or zinc-plated tools on the exhaust system. Exhaust  system parts should never be marked with a lead pencil. The  lead, zinc, or galvanized mark is absorbed by the metal of the  exhaust system when heated, creating a distinct change in its  molecular structure. This change softens the metal in the area  of the mark, causing cracks and eventual failure. After the installation of a complete exhaust system and all  pieces of engine cowl are installed and secured, the engine  should be operated to allow the exhaust system to heat up  to normal operating temperatures. The engine is then shut  down and the cowling removed to expose the exhaust system.  Each clamped connection and each exhaust port connection  should be inspected for evidence of exhaust gas leakage.  3-24 Figure 3-41.  A radial engine exhaust collector ring is graduated in  size from the inboard side to the outboard side. A C B D E F Clamp assembly Telescoping flange Main exhaust segment Engine diaphragm Clamp assembly Clevis pin & washer A B C D E F Reciprocating Engine Exhaust System Maintenance  Practices Exhaust System Inspection Manifold and Augmentor Exhaust Assembly Figure 3-40.  Elements of an exhaust collector ring installed on a  radial engine.