If any pump has low output pressure, the appropriate switch PRESS light illuminates and the pump pressure EICAS message (eg L FWD FUEL PUMP) is displayed. To prevent the centre tank fuel pumps dry-running, a modification is in hand to automatically shutoff a pump if the associated fuel pump pressure transmitter detects low output pressure for 14 seconds. (As installed) The right fuel override pump will supply fuel if both AC buses fail and the hydraulic motor generator comes on. As an engine is started and N2 RPM increases above 50%, the inhibit is removed for the associated centre tank pump. Thus both centre tank pumps are inhibited with the engines shutdown. To reduce electrical loads, the centre tank pumps are inhibited, both in flight and on the ground, when the associated N2 is Less than 50% RPM. When all six pumps are operating, the centre tank pumps override the left and right main tank pumps so that centre tank fuel is used before left and right main tank fuel. The two centre tank fuel pumps have approximately twice the output pressure of the left and right main tank fuel pumps. A single pump can supply sufficient fuel to operate one engine under all conditions. Although a repair may be needed for major failures, a simple recalibration may cure an inaccuracy.Flight crew reset of tripped fuel pump circuit breakers in flight is prohibited.Įach fuel tank contains two AC-powered fuel pumps. The Load Select Indicator problems can range from an improper or intermittent display to no display at all.Ĭorrosion on pins or connectors can cause inaccurate or intermittent readings throughout the system. The Load Select Control may also experience intermittent thumbwheel switch positions and it is often the victim of corrosion around the connector. The Fuel Quantity Indicator may exhibit issues such as a sluggish or sticking pointer, an oscillating pointer or simply an inaccurate reading. You may have to rock the switch back and forth through a position to get a solid reading. Worn switches can lose that “detent” feeling, where the switch decisively goes into a chosen position. The Selector Switch has a large wager switch that can become intermittent if the contacts get dirty or worn. The following are common problems seen on these components. If there is a smaller discrepancy, the problem could go unnoticed. For example, differing readings are obtained when the selector switch is rocked back and forth to a single position. Other times, the squawks may be intermittent. What could possibly go wrong with such a system? Sometimes the problems are obvious, such as when the indicator reading is way off from the known quantity of fuel. This indicator is provided with a test function, which temporarily drives the pointer to the empty position from whatever position it is at to verify proper system operation. This fuel gauge has a pointer display, showing the fuel quantity in thousands of pounds or kilograms. This switch selects which value is displayed on the JG911 Fuel Quantity Indicator. The RG55 Selector Switch is used to select a reading of any individual tank or a total of all of the tanks. The Load Select Indicator is solder sealed to reduce exposure to moisture and the possibility of the ensuing corrosion.įor the pilot, two other units are called into play for the reading of fuel quantity from the cockpit. The top display shows the quantity of fuel in the tanks and the bottom display shows the quantity of fuel selected to be loaded. The Load Select Indicator has two LCD displays. The Load Select Control uses numbered thumbwheel switches to select the quantity of fuel to be pumped into the tanks. They are typically housed in a panel, under the wing. It consists of the RG1017 Load Select Control and the JG1208 Load Select Indicator. Your aircraft may have a system similar to the following Honeywell example. Getting a specific amount of fuel into the proper tanks is the job of the Load Select System. Measuring the fuel on an aircraft can be a challenging task, with some larger models having as many as seven fuel tanks located in the fuselage, left and right wings, left and right tips and left and right auxiliaries. Unlike an automobile, if you run out of fuel, you can’t just simply coast to a stop. The Anatomy of a Fuel Quantity Indication System January 2015įew things are more important during a preflight check or while in flight than accurately knowing how much fuel is on board.
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