plate. This procedure varies greatly with different types of aircraft. You must use the applicable MIM to perform a leveling procedure. Lowering Aircraft Make sure that landing gear safety pins are installed. Make sure that the arresting hook is retracted. Install arresting book safety pin, or verify that it is installed. Verify that the landing gear handle in the flight station is in the DN (down) position. Lubricate exposed surfaces of the shock strut piston and nose oleo strut with clean hydraulic fluid. NOTE: Wiping down oleo struts with hydraulic fluid helps to prevent them from sticking. Apply jacking pressure and loosen the lock collar on wing jacks and nose jack. Lower all jacks evenl y and slowly, while maintaining preload on tiedown chains by manually rotating tensioning grips. Lower jacks until landing gear wheels are on deck and jacks are clear of jack pads by a safe margin. CAUTION Jacks should be promptly removed from the aircraft’s underside to prevent structural damage to the aircraft in the event of settling. WARNING Make sure that the aircraft main and nose landing gear struts have settled to their normal position prior to entering main or nose landing gear wheel wells. Failure to allow landing gear to settle could result in personnel injury. Install chocks and apply parking brakes. Remove jacks. Remove jack adapters and install/remove aircraft mooring adapters and tiedown chains as required by the MIM. Secure the aircraft, and ensure all protective covers and ground safety devices are installed. Clean up area and stow all equipment. AIRFRAME FUEL SYSTEM Learning Objective: Recognize the different types of aircraft fuel cells and repair procedures for integral fuel cells. Airframe fuel system maintenance is the responsibility of more than one work center. For instance, ADs remove and install bladder and self-sealing fuel cells. Personnel of the AM rating perform the repairs on integral tanks. Personnel from the AO rating usually help in the installation and removal of external tanks (drop tanks). To meet the particular needs of the various types of aircraft, fuel tanks vary in size, shape, construction, and location. Sometimes a fuel tank is an integral part of a wing. Most often fuel tanks are separate units, configured to the aircraft design and mission. FUEL TANK CONSTRUCTION The material selected for the construction of a particular fuel tank depends upon the type of aircraft and its mission. Fuel tanks and the fuel system in general are made of materials that will not react chemically with any fuels. Fuel tanks that are an integral part of the wing are of the same material as the wing. The tank’s seams are sealed with fuelproof sealing compound. Other fuel tanks may be synthetic rubber, self-sealing cells, or bladder-type cells that fit into cavities in the wing or fuselage of the aircraft. Fuel tanks must have facilities for the inspection and repair of the tank. This requirement is met by installing access panels in the fuselage and wings. Fuel tanks must be equipped with sump and drains to collect sediment and water. The construction of the tank must be such that any hazardous quantity of water in the tank will drain to the sump, so the water can be drained from the fuel tank. The AM should be familiar with the different types of fuel tank/cell construction, as described in the following text. Self-Sealing Fuel Cells A self-sealing cell is a fuel container that auto- matically seals small holes or damage caused during combat operations. A self-sealing cell is not bulletproof, merely puncture sealing. As illustrated in figure 3-31, the bullet penetrates the outside wall of the cell, and the sticky, elastic sealing material surrounds the bullet. As the bullet passes through the cell wall into the cell, the sealant springs together quickly and closes the hole. Now some of the fuel in the tank comes in contact with the sealant and makes it swell, completing the seal. In this application, the natural stickiness of rubber and the basic qualities of rubber and petroleum seal the hole. This sealing action reduces the tire hazard brought about 3-44