King Air B200 - Fuel System
FUEL SYSTEM Auxiliary tank
Auxiliary tank The Auxiliary tank on each side is a solitary bladder-type tank in the center section between the main and rear spars. It has its own filler cap in the center section. Since the auxiliary fuel will not flow into the main tank by the action of gravity, it has a Transfer system which utilizes a jet pump to move the fuel into the main tank. More about the Transfer system will be presented shortly. Beneath both filler caps is a short inlet neck terminated with a flapper which is spring-loaded to the closed position. This anti-siphon valve is designed to prevent loss of large amounts of fuel in the event that the cap is not secured.
FUEL SYSTEM LIMITATIONS
LIMITATIONS The following fuel management limitations are stated in the FAA Approved Airplane Flight Manual. 1. Do not put any fuel into the auxiliary tanks unless the main tanks are full. 2. Maximum allowable fuel imbalance between wing fuel systems is 1,000 pounds. it is difficult to keep the airplane rolling straight after touchdown and while taxiing...it really wanted to pull to the heavier side! 3. Do not takeoff if fuel quantity gauges indicate in yellow arc or less than 265 pounds in each main tank. Yellow arc 265 pounds = 30 min - VFR day reserve 4. Crossfeeding of fuel is permitted only when one engine is inoperative. 5. Operation of either engine with its corresponding Fuel Pressure annunciator illuminated is limited to 10 hours before overhaul or replacement of the engine-driven high-pressure pump. Do not put any fuel into the auxiliary tanks unless the main tanks are full.
FUEL SYSTEM DIFFERENCE BETWEEN CROSSFEED and TRANSFER
Notice that crossfeed always refers to fuel moving from one main tank to the opposite engine. It must not be confused with "Transfer," which refers to fuel moving from the aux to the main tank on the same side.
Q&A; 1. What will be the result if the high-pressure, engine-driven fuel pump quits?
Remember that any boost pump is not strong enough to run the engine. If the high-pressure pump quits, the engine quits.
Q&A: 5. "Fuel Crossfeed" refers to the action of taking fuel from ____________________ and sending it to _________________________________________.
5. "Fuel Crossfeed" refers to the action of taking fuel from one main tank and sending it to the opposite engine.
FUEL SYSTEM Fuel Vent System Two purposes
Fuel Vent System Diffences Prior to BB-666) 2 purposes. ● allows air to enter the tanks to keep positive pressure applied on the fuel, so that a vacuum would not be created as the engine consumes fuel. ● provides a path for fuel to escape if the tanks are overfilled or if they build up excessive pressure due to thermal expansion.
Q&A: 4. "Fuel Transfer" refers to the action of taking fuel from ____________________ and sending it to _________________________________________.
"Fuel Transfer" refers to the action of taking fuel from AUX and sending it to main tank on the same side
FUEL SYSTEM Fuel shutoff - Purge Valve prior to BB-666 . BB-667 and after -
A line extends from the FCU, back through the firewall, and into the nacelle portion of the main tank. This line contains a normally-closed solenoid valve called the "Purge Valve." Whenever the starter and/or the ignition is operating, this valve is energized open to provide a path for vapor bubbles to be purged out of the FCU and returned to the tanks. In that manner, the fuel which reaches the nozzles is a steady stream of liquid, instead of a bubble-filled stream of liquid and vapor. If vapor is not purged from the system, combustion can alternately start and stop...leading to temperature fluctuations which can cause premature combustion chamber distress. There is an easy way in which proper operation of the purge valve may be confirmed. When it is open, during start, the fuel flow gauge should indicate about 10 - 20 pph more fuel flow than the engine is receiving. Since the fuel flow transmitter is installed upstream of the FCU and upstream of the purge valve, the extra flow going back into the tanks will be registered on the flow meter. Consequently, watch the fuel flow gauge when you turn off the start switch after the engine stabilizes following the start. You should observe a small decrease in flow, showing that the valve had been open and now has sprung back to the closed position. For serials prior to BB-225, the inverter must be on before the fuel flow gauges operate. Hence, the check for purge valve operation during a normal start cannot be accomplished, since the inverter is usually not turned on until after the second start. By the way, if you ever observe a huge fuel flow change—perhaps 200 pph—we bet that the 0.018" orifice which is supposed to be installed in the purge line is missing. Perhaps it got accidentally discarded somewhere in the past when the hose was replaced....get another one installed.
FUEL SYSTEM ABNORMAL PROCEDURES
ABNORMAL PROCEDURES Pages A4 and A5 of King Air Academy's Emergency and Abnormal Checklist cover potential fuel system malfunctions. Read these procedures now. (You will find them in the Flight Training Notes book, next-to-last chapter.)
FUEL SYSTEM LIMITATIONS - USING AVGAS
Additionally, when aviation gasoline is used as an emergency fuel... 1. Operation is limited to 150 hours between engine overhauls. 2. Operation is limited to 20,000 feet pressure altitude or below if either Standby boost pump is inoperative. 3. Crossfeed capability is required for operation above 20,000 feet pressure altitude. Let's examine each of these limitations and learn some of the reasons behind them.
FUEL SYSTEM How often drain fuel?
Begin by draining all locations before the first flight of the day. If possible, do it before the airplane has been moved, so there is more chance that the heavier contaminants will have settled and stayed down at the drain locations After you have done this four or five times, and if all locations are coming out clean consistently, then—only then—consider increasing the time interval between the messy draining chore. We get uneasy when more than a month goes by without all drains being given attention. Remember, according to the Flight Manual—the "Bible" for operation—it is always done as part of a complete preflight inspection.
FUEL SYSTEM Fuel Vent System
Beneath the wing just outboard of the main wheel well are two openings into and out of the fuel vent system. First opening which is recessed into the wing skin in such a manner that its blockage with ice is unlikely. Second opening is at the end of a short pipe, and it is angled to receive ram air pressure into the vent as the airplane flies. Since this pipe is a likely ice collector, it is wrapped with a wire heating element protected inside a rubber sheath. The appropriate (left or right) Fuel Vent Heat switch in the cockpit sends current to the heating element. Both of these openings feed air to the same vent lines, so that if either one is open all the tanks (main and auxiliary) should receive positive pressure. However, the design of the lines and an associated check valve direct any fuel which must vent overboard to flow only through the heated pipe vent so that it will drop free and clear of the wing structure and pose less hazard of fire or explosion.
FUEL SYSTEM Fuel Vent System additional back up fuel vent
Beside the two main opening for fuel vent there is another path through which air can enter the main tank. It is a small hole in the bottom wing skin near the wing tip. In the unlikely event that the recessed and heated vents both are blocked, or that the line they connect to become clogged, then a vacuum relief valve will open when the engine has consumed enough fuel to create a slight suction in the tanks, and air will be drawn in through this opening. This opening is meant only as an alternate air inlet path to the tanks. If any fuel is observed dripping from this vent during your preflight inspection, it is incorrect...indicative of a leaky check valve or loose connection. If the narcelletank is full the fuel will vent into the aux tank first. Only if the auxiliary tank were full should expanding fuel vent onto the ramp through the heated fuel vent.
FUEL SYSTEM CROSSFEED
CROSSFEED When the crossfeed switch is moved from its center, closed, position to the right, three actions should occur. 1. The crossfeed valve should energize open, to provide a path for fuel flow to the opposite engine, and the Crossfeed annunciator should illuminate. 2. The left standby pump should come on, to provide the pressure which will shove the fuel to the other side. 3. The right aux transfer system should shut down, to prevent flow of fuel into the right tanks and, perhaps, overboard. Items number 2 and 3 are reversed when the switch is moved to the left. Notice what the crossfeed switch does not do. It does not turn off the other standby pump. If that pump were on, then both pumps would be fighting each other and little if any crossfeed would occur. Also, it will not turn off the opposite transfer system if its switch is in the "Override" position. The switch must be in its normal, "Auto" position. During crossfeed, the fuel flows to the opposite side propelled by the pressure of the standby pump. As it arrives on the opposite side, it tries to enter the nacelle tank, but check valves slam closed to prevent that from happening. Consequently, all fuel which is consumed by the engine is supplied from the opposite side's main tank. Notice that we have now presented three purposes served by the standby pump. (1) It is to be used in the event of engine-driven boost pump failure, which is denoted by illumination of the Fuel Pressure annunciator. (2) It is used for crossfeed to the opposite engine. (3) It is necessary for operation with gasoline at altitudes above 20,000 feet. Notice that crossfeed always refers to fuel moving from one main tank to the opposite engine. It must not be confused with "Transfer," which refers to fuel moving from the aux to the main tank on the same side.
FUEL SYSTEM Crossfeeding Reason for this limitation: Crossfeeding of fuel is permitted only when one engine is inoperative.
Crossfeeding of fuel is permitted only when one engine is inoperative. This is a strange one. It comes from concerns originating in Beech's legal team, not their engineering team. When the pilot crossfeeds fuel in a King Air, it is being fed directly to the engine on the opposite side, it is not flowing into tanks on the opposite side. Notice the word...crossfeed. It is quite possible—and very easily, although illegally, done—to feed fuel from one main tank to both engines simultaneously. When a fuel imbalance occurs, this is a desirable means of reestablishing balance...feeding fuel from the heavy side to both engines until the weight is even. The pump capacity and line size are sufficient for this purpose. It works well, but it cannot be done legally. Whenever two independent powerplants are receiving their fuel from a common system, the exposure to risk is greater than if each engine is receiving fuel from its own system. Obviously, fuel contamination or starvation is unlikely to effect both engines at the same time if they have separate fuel supplies. Realizing this, it would be prudent to crossfeed for fuel balancing purposes only at a safe, high, altitude. In the unfortunate situation of forgetting what we are doing and running the feeding tank dry, we would at least have enough altitude and time to conduct a restart attempt using fuel from the other side's tank. But back in the 70's, a Travel Air (Beech Model 95) was not so fortunate, and all on board died in the crash which followed after simultaneous fuel starvation of both engines. The wreckage was found to have fuel on one side only and Beech was found liable in a law suit which resulted from this tragedy. Ever since, almost all twin-engine Beechcrafts have contained this limitation.
Q&A: 3. Which filler cap should be serviced first when full fuel is desired?
Do not put any fuel into the auxiliary tanks unless the main tanks are full.
Q&A 10. The airplane contains a total of __________ fuel drains and __________ fuel vents.
Each side's fuel system contains six drains for a total of twelve. Two vents into and out of the fuel vent system. One of these is an opening which is recessed into the wing skin in such a manner that its blockage with ice is unlikely. The other opening is at the end of a short pipe, and it is angled to receive ram air pressure into the vent as the airplane flies.
FUEL SYSTEM FUEL ADDITIVES approved
FUEL ADDITIVES Two fuel additives are approved—Prist and Biobor JF. Prist is the well-known anti-icing additive which also provides a biocidal action which helps to kill any growth of microbiological slime which can thrive in the fuel-water interface in the tanks. Biobor is used exclusively as a biocidal agent. If greenish, goopy, slime shows up in your fuel drain samples, then a treatment of Biobor can make a positive improvement. The airplane is equipped with an oil-to-fuel heat exchanger which heats the fuel automatically using engine oil. It must be extremely cold before the oil will not contain sufficient energy to heat the fuel, as shown by the chart in the Limitations section of the POH entitled "Minimum Oil Temperature Required for Flight." No additive needs to be added to the King Air's fuel system during typical operation.
FUEL SYSTEM Fuel Drains and Location
FUEL DRAINS Each side's fuel system contains six drains for a total of twelve. These are... 1. Integral Tank drain, on the outboard wing aft of the tie down ring. 2. Leading Edge Tank drain, just outboard of the nacelle slightly behind the wing's leading edge. 3. Gravity Feed Line drain, either behind the wheel well or, for those with factory-installed hydraulic landing gear, outboard of the wheel well on the skin above the gear door. 4. Nacelle Tank Strainer drain, behind an access hole in the skin forward of the wheel well. 5. Firewall Fuel Filter drain, in the same area as the nacelle tank drain, but a little farther forward. 6. Auxiliary Tank Strainer drain, beneath the center section near the fuselage. There is actually a seventh drain also, right beside the nacelle tank drain, which comes from the bottom of the Standby Pump. However, this drain is plugged with a large Allen-head screw and is only for use by maintenance personnel when they are draining the system. The drains above numbered 1, 3, 4, and 5 are all of the same type...flush mounted drains which contain a center button which must be pushed open with a tool to allow the drain to function. Begin by draining all locations before the first flight of the day. If possible, do it before the airplane has been moved, so there is more chance that the heavier contaminants will have settled and stayed down at the drain locations
FUEL SYSTEM CAPACITIES
FUEL SYSTEM Total usable fuel capacity is 544 U.S. gallons • 193 gallons contained in each main tank (left and right) and • 79 gallons contained in each auxiliary tank (left and right). Less than seven gallons are unusable. When filled with Jet A fuel at a typical density of 6.7 pounds per gallon, • both main tanks together hold 2,586 pounds and the aux tanks hold a total of 1,059 pounds, for an airplane total of 3,645 pounds. In round numbers, you have 2,600 pounds when the main tanks are full and an extra 1,000 pounds when the aux tanks are full.
FUEL SYSTEM FUEL TRANSFER SYSTEM
FUEL TRANSFER SYSTEM The transfer of fuel from the aux to the main tank is usually completely automatic. The aux transfer module receives power from the Aux Transfer circuit breaker and makes an electronic "decision" whether or not to supply this power to the motive flow valve. To make its decision, the module receives three bits of information. First, it knows when the boost pump pressure exceeds 10 psi (using the same switch which extinguishes the Fuel Pressure annunciator), since to open the motive flow valve before sufficient pressure exits to force fuel through the transfer jet pump would be pointless. Second, it knows whether or not there is fuel in the aux tank, as sensed by a float switch at the tank bottom. Third, it senses when crossfeed is activated, so that it may shut down automatic transfer on the side being fed. Fuel transfer system. When Override is selected, the automatic fuel transfer module is completely bypassed. If fuel exists in the aux tank prior to engine start, then the "No Transfer" light on the fuel panel should be illuminated after the battery is turned on, prior to start. As the starter begins spinning the engine and the engine-driven boost pump begins supplying pressure, the module receives this information. After a 30 to 50 second time delay, the module sends power to the motive flow valve, causing it to open and thereby beginning transfer. The time delay is provided so that the motive flow valve will not open—and will not reduce the pumping effectiveness of the boost pump—when it is at low speeds during the early stages of a start. When the motive flow valve opens, the fuel which is permitted to flow to the jet transfer pump passes a 6 psi pressure switch. It is the inflation of this switch which causes the No Transfer light to extinguish. Pressure could exist at the 6 psi switch even though no transfer were taking place. For example, suppose that a rag fell into the aux tank filler cap and got sucked into the jet pump's pick-up port. In that event, no fuel would be transferred through the clogged pump even though the No Transfer light were extinguished. The only sure way of knowing that transfer is taking place is to monitor the fuel quantity gauges over a period of time...
FUEL SYSTEM NORMAL FUEL FLOW FROM NACELLE TANK TO ENGINE
Fuel is drawn out of the nacelle portion of the main tank by the suction provided by the engine-driven boost (low-pressure) pump. The fuel flows through the open firewall shutoff valve on its way to the boost pump. As it leaves the boost pump—under a typical pressure of about 30 psi—it then proceeds through the firewall fuel filter and the fuel flow transmitter before it reaches the oil-to-fuel heat exchanger. The next component it reaches is the high-pressure pump, where it is discharged at pressures which can approach 1,000 psi. From there it goes to the Fuel Control Unit (FCU), where it is metered and sent to the combination Flow Divider/Dump Valve located at the bottom of the two fuel manifolds which surround the engine. The flow divider feeds both the primary and secondary fuel manifolds, which in turn feed the appropriate fuel nozzles.
Q&A: 9. What is the maximum allowable fuel imbalance limitation, if any?
Maximum allowable fuel imbalance between wing fuel systems is 1,000 pounds.
FUEL SYSTEM Fuel Vent System Nacelle vent details.
Nacelle vent details. During normal operation, air from the aux tank vents into the nacelle tank and fuel expanding from the nacelle—due to thermal expansion or due to the pressure build-up which occurs while transferring—returns to the aux tank. Since the top of the nacelle tank is slightly lower than the top of the wing tip, when pressure builds up in the main tank the pressure felt against the top of the nacelle tank will be slightly greater than that felt at the wing tip. Therefore, fuel will be more likely to push through a pressure relief valve located at the nacelle top and find a path to flow into the aux tank. More often than not, the aux tank would not be full, so this expanding fuel could be received there, stored, and transferred back into the main tank when the engine is running...never wasted overboard onto the ramp. Only if the auxiliary tank were full should expanding fuel vent onto the ramp through the heated fuel vent.
Q&A: 2. What purpose does the boost pump serve? List as many purposes as you can.
Notice that we have now presented three purposes served by the standby pump. (1) It is to be used in the event of engine-driven boost pump failure, which is denoted by illumination of the Fuel Pressure annunciator. (2) It is used for crossfeed to the opposite engine. (3) It is necessary for operation with gasoline at altitudes above 20,000 feet.
FUEL SYSTEM NORMAL "INTERIOR PREFLIGHT" PROCEDURES
On the first flight of the day, the "Interior Preflight" checklist presents a procedure for thoroughly testing most of the important fuel system components. The steps of the procedure are: 1. Fuel Firewall Valves—CLOSED (listen for operation). Since the shutoff valves are wired directly to the hot battery bus, you should be able to hear the valve motors momentarily operate as the valves close, even before the battery switch is turned on. Leave the valves closed (which means the red guards over the switches will be open) for now. 2. Standby Pumps—ON (listen for operation). For serials prior to BB-1096, these pumps also are hot-wired. Leave the switches on. 3. Battery Switch—ON (Fuel Pressure lights verify on). Now all electrical buses are powered, and the annunciator panels begin to operate. If the firewall valves are operating properly—not allowing fuel to leak past them—then the Fuel Pressure lights should be illuminated. 4. Fuel Firewall Valves—OPEN (Fuel Pressure annunciators extinguish). This verifies that the valves have properly opened and that the fuel pressure switches are working correctly...causing the annunciators to extinguish when pressure is present. 5. Standby Pumps—OFF (Fuel Pressure lights come back on). No pumping, no pressure. 6. Crossfeed Switch—ALTERNATELY LEFT AND RIGHT (verify Crossfeed annunciator illuminates and both Fuel Pressure annunciators extinguish.) The Crossfeed annunciator only confirms crossfeed switch position, it does not verify that the valve actually opened nor that the appropriate standby pump began operation. It is very important to listen for the standby pump on the side you are crossfeeding from, and confirm that both Fuel Pressure lights extinguish...now we know that pressure from the proper pump is flowing to both sides, so the valve must truly be open. 7. Crossfeed Switch—OFF (Crossfeed annunciator goes off and both Fuel Pressure annunciators come back on.) 8. Aux Transfer Switches—AUTO. Verify that the switches are in the down, "Auto," position. If they are in the up, "Override," position, ask yourself why. Was someone "playing" in the cockpit? Or was there a malfunction which the previous crew forgot to tell you about? If the switches are up, less fuel pressure will
FUEL SYSTEM Fuel Vent System Nacelle and aux tank fuel exchange problems
One of these problems involves fuel draining from the nacelle back into the aux tank even when there is no thermal expansion causing it! This is not correct, and your service shop would need to give it some attention to repair the problem. One of the valves which connect the nacelle tank to the aux tank is probably leaking.
FUEL SYSTEM Fuel tank considerations
Tanks and filler caps. To reduce wing bending stress, the main tanks should be filled first and consumed last. Tactfully tell the refueler to fill the outboard caps first and then, if the truck is still working and if you want more fuel, put the rest in the inboard caps.
FUEL SYSTEM Fuel shutoff - residual fuel in the manifolds prior to BB-666 . BB-667 and after -
The fuel shutoff valve operated by the condition lever is located in the FCU. When the lever is pulled into the Fuel Cutoff position, fuel flow is terminated. Fuel flow is terminated with the condition lever. prior to BB-666: At this time, for serials prior to BB-666, residual fuel in the manifolds drains back through the Dump valve into the Fuel Drain Collector tank. A float-activated switch in that tank turns on the Fuel Drain Collector pump which returns this residual fuel back into the main tank. This is the system often known as the "EPA kit" which keeps residual fuel from contaminating the ramp after every shutdown. For BB-667 and after For BB-667 and after, the complexity of collector tank, float switch, and pump were eliminated, replaced by a metal cylinder called the Purge Tank, or Purge Accumulator. P3 air pressurizes this tank when the engine is running. Fuel is prevented from coming back into the tank by a check valve between the tank and the dump valve. After the fuel flow is terminated with the condition lever—as residual fuel pressure in the manifolds decreases—the fuel pressure becomes less than the pressure in the P3 accumulator. At that time, the P3 air pushes through the check valve to shove the remaining fuel through the nozzles with enough force to provide good atomization of the fuel and proper combustion. In that manner, the last bit of fuel is properly burned instead of dribbling into the combustion chamber, evaporating, and exiting through the engine's exhaust stacks as thick white smoke. To provide sufficient P3 accumulator pressure so that the fuel purge works correctly, avoid shutdowns right after engine start. Power the engine up to 90% N1 or more at least once prior to shutdown, when possible.
FUEL SYSTEM Main Tank
The term "Main Tank" refers to a combination of six interconnected tanks on each side—the nacelle tank and five more tanks in the outboard wing section. All of these tanks are the rubberized bladder-type with one exception...the tank between the main and rear spars in the outer half of the outboard wing's "box section" is an integral tank, or wet cell. Due to the dihedral of the wing, all fuel from the five tanks in the outboard wing will flow into the nacelle tank. Thus the system acts as one large tank, with the high point near the wing tip where the filler cap is located and the low point at the bottom of the nacelle tank, where the Standby pump and fuel pickup point are located
FUEL SYSTEM There is a handy and easy method of converting pounds of jet fuel to gallons when the density is 6.7 pounds per gallon. ....
There is a handy and easy method of converting pounds of jet fuel to gallons when the density is 6.7 pounds per gallon. Simply add half of the pounds to itself. Or, expressed another way, multiply the number of pounds by 1.5. The answer you obtain is the number of gallons...except it is 10 times too large. So move the decimal point one space to the left (divide by 10) and you will have the final answer. Expressed as a formula... (Pounds + Half the Pounds) ÷ 10 = Gallons Example: Need to add 800 pounds to the left side? Then order 120 gallons. You are burning 600 pounds per hour in cruise today? That's 90 gph. Y ou shut down with 400 pounds left on each side and you told the FBO to "fill the mains?" Then you should see about 270 gallons on the fuel bill. (2,600 pounds for full fuel, minus the 800 pounds remaining, equals 1,800 pounds to add. 1,800 pounds equates to 270 gallons.)
FUEL SYSTEM High pressure Fuel Pump issues Reason for this limitation: Operation of either engine with its corresponding Fuel Pressure annunciator illuminated is limited to 10 hours before overhaul or replacement of the engine-driven high-pressure pump.
When the Fuel Pressure annunciator is on, it is telling us that there is less than about 10 psi of pressure being applied to the inlet side of the high-pressure engine-driven fuel pump—the only pump strong enough to run the engine. Without sufficient pressure applied, this pump is prone to cavitation...the formation and subsequent collapse of vapor bubbles in a liquid caused by insufficient pressure If a pump is capable of creating very high discharge pressures, it is usually of the positive displacement type...the fit between the gears or vanes and the pump housing is tight. Little if any "slippage" occurs, and for each revolution of the drive shaft a fixed quantity of fuel is delivered. These types of pumps are not only capable of creating very high discharge pressures, but they are also capable of creating very low inlet pressures. They really suck! They can suck so much—make the inlet pressure so low—that the liquid fuel actually starts to boil, or evaporate. (We know that water boils at a lower temperature than 212°F at altitudes above sea level. Like most liquids, its boiling point is reduced as pressure is reduced. The same is true of fuel.) Bubbles of vapor created by this suction begin to pass through the pump. Since vapor does not cool and cushion as well as liquid, the pump's internal lubrication suffers and it begins running hotter. Even worse, the bubbles eventually find themselves surrounded by high pressure liquid as they get nearer the discharge side, and they are squeezed smaller and smaller until they finally "implode" back to liquid. This implosion can be violent enough to actually erode tiny bits of metal from the pump's parts. Eventually, the pump can be so damaged that it is prone to leakage or even total failure. In summary, the inlet or suction side of the high-pressure pump must not be allowed to operate at such a low pressure that cavitation could begin. The purpose of the boost pump is to prevent cavitation. It does this by maintaining a pressure of about 30 psi at the high-pressure pump's suction side. Remember that any boost pump is not strong enough to run the engine. If the high-pressure pump quits, the engine quits. There are two boost pumps on each side...an engine-driven one
