GENERAL
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4-30-2 Repair or Replace the Damaged Landing Gear
1.  Initially, try to repair the damaged gear if the necessary parts and tools are available. Here are some examples of repaired landing gears. Similar procedures may be applicable to the model 757 airplanes.
A.  Figure 4-24 shows a welded side strut on a model 727 main landing gear. The repaired main landing gear permits you to tow the airplane to the runway.
B.  In one example, the lower side strut on a model 707 main landing gear was replaced to permit the airplane to be towed on its own landing gear.
C.  In a different incident, a model 707 airplane makes a short landing before the runway. The landing causes damage to a main landing gear truck and its inner (oleo) cylinder. The damaged main landing gear is in the DOWN position. The recovery persons remove a length of the damaged inner cylinder. There is 12 to 14 inches (30 to 36 cm) of a good remaining cylinder. They put this remaining inner cylinder into the outer cylinder and tow the airplane to a repair area.
D.  Frequently, you can apply a temporary brace to a damaged side strut or a damaged drag strut. The landing gear must be in the extended position. Then these braces are a fast solution that permits you to tow the airplane to a repair area.
2.  If a landing gear is available, a full replacement of the damaged gear is your best solution. Make sure that there is no structural damage to the gear support areas.
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4-30-3 Extend the Folded Gear
1.  Landing gear alternate extension is done by an electrical/hydraulic/mechanical system that operates independently from the normal extension and retraction system. This system releases the locks on the landing gear and doors when the normal hydraulic system does not work.
When the ALTN EXTENSION (see Figure 4-25) is pushed two alternate extension control relays are energized. The power is supplied by the 28 Vdc battery bus. The ALTN EXT CONT relay sends electrical power to the power pack. The power pack removes fluid from the left hydraulic reservoir. It supplies the hydraulic fluid to the door lock release actuators for the landing gear. These actuators extend and mechanically release the internal locks in the door actuators. The landing gear doors now start to free fall open.
When the door lock release actuators are fully extended, internal valves send the hydraulic fluid through to the alternate uplock release actuators for the nose and main landing gears. These actuators extend and mechanically release the locks for the landing gear. The landing gears now start to free fall to the down-and-locked position.
　
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