28 Fuel System-Tanks, vents, drains etc.
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TTP |
B1-L3 |
ATA 28 |
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Beech 90 Series |
B2-L2 |
Fuel Systems |
GENERAL
Fuel is stored in nacelle and interconnected wing tanks on each side of the airplane. The engines draw fuel from the nacelle tanks,which are fed from the wing center section and outboard tanks. A crossfeed system allows the fuel system on one side to feed the engine on the other side.
DESCRIPTION
The independent right and left fuel systems consist of three fuel cells in the outer wing panel, one cell in the center wing inboard of the nacelle, and one cell in the nacelle. All of the tanks are of the rubber-bladder-type. Fuel gravity feeds from the outer wing tanks into the center wing tank where the electric transfer pump sends fuel to the nacelle tank. The engine is supplied fuel from the submerged boost pump in the bot- tom of the nacelle. For fuel crossfeed operation, the left or right fuel system can be connected to the opposite engine by a valve-controlled crossfeed line. Total usable fuel capacity is 192 U.S. gallons on each side for a total fuel load of 384 U.S. gallons.
FUEL-HANDLING
PRACTICES
All hydrocarbon
fuels contain dissolved and suspended water. The quantity
of water contained in the fuel depends
upon the temperature and type of fuel. Jet fuel, with its higher aromatic content,
tends to absorb and suspend
more water than aviation gasoline. Along with the water, it suspends
rust,
lint, and
other foreign materials longer.
Since most suspended materials can be
removed
from the
fuel
by sufficient settling time and proper filtration, they are not a major problem. After
refueling, allow a three-hour settling period whenever possible, then drain a small amount of fuel
from each drain.
JET FUEL ADDITIVE
The additive for jet fuel is primarily an anti-icing agent, but also has excellent microbiological- sludge-deterrent characteristics. Very soluble in water, but only slightly soluble in fuel, this additive must be precisely blended into the fuel by a metering device that permits injection of the agent into a flowing stream of fuel to ensure even dispersal. Fuel distributors may tank, batch blend, or may prefer to blend at the airplane when refueling. If the tanker truck is not equipped with the proper metering device, it may be necessary to carry the anti-icing agent and the blending device in the airplane. When blending the anti-icing agent with fuel, the concentration of additive should not be less than 20 fluid ounces per 260 gallons of fuel or more than 20 fluid ounces per 104 gallons of fuel. When adding previously blended fuel, the additive concentration should not be less than 0.06% by volume or more than 0.15% by volume. This additive should be used on a continuous basis.
SERVICING Fuel
All approved jet fuels (Jet A, Jet A-1, Jet B, JP-4, JP-5, and JP-8) may be mixed in any ratio. Aviation gasoline grades 80/87, 91/96, 100LL/130, and 115/145 (as an emergency) fuel may be mixed in any ratio with the normal fuels when necessary. However, use of the lowest octane rating available is suggested due to its lower lead content. The use of aviation gasoline shall be limited to 150 hours of operation during each time-between-overhaul (TBO) period. If aviation gasoline is used as an emergency fuel, the hours of operation on gasoline must be calculated to avoid exceeding the maximum of 150 hours of operation between overhauls.
Filling the Tanks
The King Air C90 Series has two filler caps on each side. One fuel cap, to fill the nacelle tank, is on top of the nacelle. The other cap, to fill the wing tanks, is in the outboard leading edge fuel cell. The nacelle tank should be filled first. Check valves in the nacelle keep the nacelle tank fuel from back flowing into the wing tanks. The wing tanks are to be serviced only after the nacelle tank is full. If the wing tanks were filled before the nacelle tank fuel from the wing tank could flow into the nacelle tank, the aircraft would not have a full fuel load.
Whenever possible, allow a three-hour settling time after refueling. After this settling period, drain at least 12 ounces of fuel from each drain point.
Defueling
To completely
defuel the aircraft tank system,
drain both the nacelle tank and the center wing tank.
VENT SYSTEM
The fuel system is vented to allow atmospheric air into the tanks as fuel is consumed from the tanks, and to allow air out of the tanks as the air- craft climbs into a lesser atmospheric air pressure. Vent lines interconnect all tanks to adjacent tanks. Pressure from the vent system exits through two parallel vents on the underside of the wing outboard of the nacelle. One vent is recessed to avoid icing; the second vent, which is heated to prevent icing, serves as a backup should the other vent become plugged. Air entering into the system comes in through the two parallel vents or a one-way check valve in the wing outboard of the fuel tanks. The check valve prevents any fuel from exiting through the outboard vent
FUEL FLOW FROM TANKS TO ENGINE
The nacelle tank feeds fuel to the engine. Normally, a boost pump feeds fuel from nacelle tank fuel to the engine, but, in the case of boost pump failure, gravity feed is available. Fuel from the boost pump, in the bottom of the nacelle tank, provides fuel pressure to the high-pressure, engine-driven fuel pump. Additionally, the boost pump provides pressure for fuel crossfeed from the nacelle tank on one side of the aircraft to the engine on the other side.
The boost pump lever lock switches are on the pilot fuel control panel. Power for the boost pumps is supplied either through 10-amp circuit breakers below the fuel control panel or through two parallel 5-amp fuses on the hot battery bus. A diode network prevents inter- action between the buses. The boost pump has an operating capability of 1,250 pounds per hour at a pressure of 30 psi.
Fuel Purge Valve
FUEL TRANSFER
Fuel gravity feeds
from the outer wing
tanks into the center wing tank;
from there the electric
transfer pump sends
fuel into the nacelle tank. The nacelle tank fuel probe has three integral switches (two upper
limit and one lower limit) that activate when
fuel is down 10 gallons from
full. The left and right fuel TRANSFER PUMP lever lock
switches on the fuel control
panel controls fuel transfer. The switch has three positions:
OFF, AUTO, and OVERRIDE.
When the switch
is in the AUTO position,
the fuel transfer system is enabled.
As fuel in the nacelle tank
drops approximately 10
gallons to the lower transfer limit switch,
the fuel transfer
pump in the sump of the center
wing tank is turned on and fuel
in the center wing tank fills
the nacelle tank until one of the two
upper limit switches closes and the transfer pump is turned off. Fuel in the nacelle
tank drops again and the
transfer cycle repeats until the center
wing tank is empty. As
the center wing tank empties, transfer
fuel pres- sure in the line between the transfer pump and
the nacelle tank drops. A 2.5-psi pressure
switch in the line closes and starts a 30-second timer; the transfer pump continues to run dry
to ensure no fuel remains in the center wing tank. After 30
seconds, the timer turns the transfer
pump off and turns on the
fuel transfer annunciator on the instrument glareshield.
The annunciator notifies the crew that the transfer is complete, there is approximately
50 gallons of fuel remaining
in the nacelle tank, and the transfer switch can be
positioned to OFF.
FUEL CROSSFEED
The fuel crossfeed
system supplies fuel
from the nacelle tank on one side to the engine on the opposite side during an engine-out condition. The
nacelle tank is connected to the engine
on the opposite wing by a single
crossfeed line routed from the outboard side of the nacelle across
the center section and to the outboard side of the opposite nacelle.
The solenoid valve can be manually opened or closed, but under normal conditions it is positioned to AUTO. In the AUTO position, the 10 ± 1 psi pressure switches on the firewall filter are incorporated into crossfeed circuit. If the boost pump fails and pressure on that side is below 10 psi, the crossfeed solenoid is powered open and the boost pump from the other side provides fuel pressure to keep the opposite high-pressure fuel pump from cavitating. When the boost pump fails, the corresponding fuel low pressure and master warning lights on the glareshield illuminate. As the automatic crossfeed functions, the crossfeed and the master caution light illuminates. Pressure in the crossfeed line builds above the 10-psi level and the low-pressure light extinguishes. The net result is the master warning and caution lights flashing with the crossfeed light illuminated.
FUEL PURGE SYSTEM
The fuel purge system ensures that any
residual fuel in the fuel manifolds
and nozzles is consumed during
engine shutdown. During engine operation, compressor discharge air (P3 air) is routed through
a filter and check valve, pressurizing
a small air tank mounted between the lower engine truss mounts. From the
air tank, the line runs through
a check valve to
the engine flow divider. On engine shutdown, fuel
pressure in the manifold subsides
and P3 pressure opens a poppet
valve in the fuel
flow divider. The
air forces all residual fuel remaining in the
fuel manifold out through the nozzles and into the
combustion chamber where it
is consumed.FUEL SYSTEM
KING AIR E90 AND
F90
Fuel System
The fuel system consists
of two separate systems connected by a valve controlled crossfeed line. The separate fuel system for each engine is further divided into a main and auxiliary fuel
system. The main system consists of a nacelle tank,
a wing leading edge tank, two box section
bladder tanks, and an integral (wet cell) tank,
all interconnected to flow into
the nacelle tank by gravity.
This system of tanks is filled from the filler
located near the wing tip. Each main system
has a total of 196 usable gallons.
Auxiliary Transfer Jet Pump
A
fuel transfer jet pump
mounted on the inboard
side of the main landing gear
wheel well transfers fuel from the auxiliary tank sump
to the nacelle tank. The transfer
jet pumps are actuated by lever lock toggle switches on the fuel control panel, which control a shutoff valve in the motive flow line.
As
long as either the primary boost pump or the standby
boost pump is operative and
there is fuel in
the
auxiliary tank, the transfer
pump feeds into the nacelle
tank when the valve is open. A light located on
the
fuel control panel, actuated by a float type switch in the
sump
of the auxiliary tank,
illuminates when the auxiliary system is empty.
Boost Pumps
The engine driven fuel pump is mounted on the accessory case in conjunction with the fuel control unit. The primary fuel boost pump is also engine driven and is mounted on a drive pad on the aft accessory section of the engine. This pump operates when the gas generator (Nl) is turning and provides sufficient fuel for start, takeoff, all flight conditions except operation with hot aviation gasoline above 18,000 feet altitude, and operation with crossfeed.
CAUTION: Operation
with the fuel pressure light on
is limited to 10 hours
between over-
haul or replacement of the Engine Driven Fuel Pump.
Operation with the fuel pressure light on is sited to 10 hours between main engine driven fuel pump overhaul or replacement period. One standby pump may be inoperative for takeoff. (Crossfeed of fuel is not available from the side of the inoperative standby pump.)
Operation on aviation
gasoline:
1. Operation is limited to 150 hours during any
one overhaul period.
2. Operation is limited to 18,000 feet altitude with either standby fuel pump inoperative.
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PTP Beech 90 Series |
B1 |
LOC |
FOT |
SGH |
R/I |
MEL |
TS |
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B2 |
LOC |
FOT |
SGH |
MEL |
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