size of the engine. The protective envelope is then carefully  gathered around the engine and partially sealed, leaving an  opening at one end from which as much air as possible is  exhausted. A vacuum applied to the container is very useful  for this purpose and is also an aid in detecting any leaks in  the envelope. The envelope is then completely sealed, usually  by pressing the edges together and fusing them with heat. Before lowering the shipping case cover over the engine,  a quick inventory should be made. Be sure the humidity  indicator card is placed so that it can be seen through the  inspection window and that everything required is enclosed  in the container. While lowering the wooden shipping case  cover into position, be careful that it does not twist and tear  the protective envelope. Secure the cover and stencil or mark  the date of preservation on the case. Also, indicate whether  the engine is repairable or serviceable. There are several types of shipping containers in use.  [Figure 8-21]  Another type allows horizontal installation  of an engine, thus eliminating the need for an extra hoist.  The engine is simply lowered onto the base portion of the  container and secured. Then, silica gel bags are packed into  the container, usually in a special section. The amount of  silica gel required in a metal container is generally greater  than that needed in a wooden shipping case, since the volume  of air in the metal container is much greater than that in the  protective envelope installed around an engine in a wooden  shipping case. Also, in the metal container the silica gel bags  must dehydrate the interior of the engine, since ventilatory  plugs are normally installed in the engine openings in place  of dehydrator plugs. All records of the engine should be  enclosed inside the shipping container or on the outside for  accessibility. A humidity indicator should be fastened inside  the containers with an inspection window provided. Then,  the rubber seal between the base and the top of the container  must be carefully inspected. This seal is usually suitable  for re-use several times. After the top of the container has  been lowered into position and fastened to the base of the  container, dehydrated air at approximately 5 pounds per  square inch (psi) pressure is forced into the container. The  container should be checked for leaks by occasional rechecks  of the air pressure, since radical changes in temperature affect  the air pressure in the container. Figure 8-21.  Turbine engine shipping container. 8-22 The lubrication system is usually drained and may or may  not be flushed with preservative oil. The engine fuel system  is generally filled with preservative oil, including the fuel  control. Before the engine can be returned to service,  the preservative oil must be completely flushed from the  fuel system by motoring the engine and bleeding the fuel  system. Always follow the manufacturer’s instructions  when performing any preservation or depreservation of gas  turbine engines. The procedures for preserving and depreserving gas turbine  engines vary depending upon the length of inactivity, the  type of preservative used, and whether or not the engine  may be rotated during the inactive period. Much of the basic  information on corrosion control presented in the section on  reciprocating engines is applicable to gas turbine engines.  However, the requirements for the types of preservatives  and their use are normally different. Preservation and Depreservation of Gas  Turbine Engines If the humidity indicator in a wooden shipping case shows  by its color that more than 30 percent relative humidity is  present in the air around the engine, all desiccants should  be replaced. If more than half the dehydrator plugs installed  in the spark plug holes indicate the presence of excessive  moisture, the interior of the cylinders should be resprayed.  If the humidity indicator in a metal container gives a safe  blue indication, but air pressure has dropped below 1 psi, the  container needs only to be brought to the proper pressure with  dehydrated air. However, if the humidity indicator shows an  unsafe (pink) condition, the engine should be represerved. Most maintenance shops provide a scheduled inspection  system for engines in storage. Normally, the humidity  indicators on engines stored in shipping cases are inspected  every 30 days. When the protective envelope must be opened  to inspect the humidity indicator, the inspection period may  be extended to once every 90 days, if local conditions permit.  The humidity indicator of a metal container is inspected every  180 days under normal conditions. Inspection of Stored Engines Engine attachments Cover Base