Aircraft Systems

• Electric fuel pump An ammeter is used to monitor the performance of the aircraft electrical system. The ammeter shows if the alternator/ • Stall warning system generator is producing an adequate supply of electrical power. • Pitot heat It also indicates whether or not the battery is receiving an • Starting motor electrical charge. Many aircraft are equipped with a battery switch that Ammeters are designed with the zero point in the center controls the electrical power to the aircraft in a manner of the face and a negative or positive indication on either similar to the master switch. In addition, an alternator switch side. [Figure 7-35] When the pointer of the ammeter is is installed that permits the pilot to exclude the alternator on the plus side, it shows the charging rate of the battery. from the electrical system in the event of alternator failure. A minus indication means more current is being drawn [Figure 7-33] from the battery than is being replaced. A full-scale minus deflection indicates a malfunction of the alternator/generator. With the alternator half of the switch in the OFF position, the A full-scale positive deflection indicates a malfunction of entire electrical load is placed on the battery. All nonessential the regulator. In either case, consult the AFM/POH for electrical equipment should be turned off to conserve appropriate action to be taken. battery power. Not all aircraft are equipped with an ammeter. Some have A bus bar is used as a terminal in the aircraft electrical system a warning light that, when lighted, indicates a discharge in to connect the main electrical system to the equipment using the system as a generator/alternator malfunction. Refer to the electricity as a source of power. This simplifies the wiring AFM/POH for appropriate action to be taken. system and provides a common point from which voltage can be distributed throughout the system. [Figure 7-34] Another electrical monitoring indicator is a loadmeter. This type of gauge has a scale beginning with zero and Fuses or circuit breakers are used in the electrical system to shows the load being placed on the alternator/generator. protect the circuits and equipment from electrical overload. [Figure 7-35] The loadmeter reflects the total percentage of Spare fuses of the proper amperage limit should be carried in the load placed on the generating capacity of the electrical the aircraft to replace defective or blown fuses. Circuit breakers system by the electrical accessories and battery. When all have the same function as a fuse but can be manually reset, electrical components are turned off, it reflects only the rather than replaced, if an overload condition occurs in the amount of charging current demanded by the battery. electrical system. Placards at the fuse or circuit breaker panel identify the circuit by name and show the amperage limit. A voltage regulator controls the rate of charge to the battery by stabilizing the generator or alternator electrical output. The generator/alternator voltage output should be higher than the battery voltage. For example, a 12-volt battery would be fed by a generator/alternator system of approximately 14 volts. The difference in voltage keeps the battery charged. Hydraulic Systems There are multiple applications for hydraulic use in aircraft, depending on the complexity of the aircraft. For example, a hydraulic system is often used on small airplanes to operate wheel brakes, retractable landing gear, and some constant- speed propellers. On large airplanes, a hydraulic system is used for flight control surfaces, wing flaps, spoilers, and other systems. A basic hydraulic system consists of a reservoir, pump (either hand, electric, or engine-driven), a filter to keep the fluid clean, a selector valve to control the direction of flow, Figure 7-33. On this master switch, the left half is for the alternator a relief valve to relieve excess pressure, and an actuator. and the right half is for the battery. [Figure 7-36] 7-31