C90 Fuel System Flashcards
Fuel Capacity Per Side
Nacelle Tanks - 61 USG
Centre Tanks - 44 USG
Wing Tanks - 88 USG
192 Usable per side
Fuel Capacity - Total
387 USG
Usable - 384 USG
Approved types
Jet A
Jet A-1
Jet B
Water suspends more into jet fuel than with AVGAS, need litmus paper or water cartridge to detect.
Fuel tends to grow microbiological fungicides.
Use of anti freeze additives (like Prist) may be required under certain operating
System Design
2 separate systems (Left & Right) connected by a cross feed system.
Fuel to each engine is supplied by the nacelle tank and an electric boost pump submerged within it
The wing tanks provide fuel to the nacelle by means of transfer pumps
The outside of the wing tank will flow to the center through gravity with Cross feeding allowing continued operation through failure of a boost pump
A manual and electrically driven firewall shutoff valve (SOV), is used to cut any fuel to the engine fuel system.
The fuel tank venting and pressurisation is then achieved by the use of heated fuel vents and a NACA style ram vent
NO FUEL XFR
No PX after 30 secs - Empty wing tanks / Pump failure / Px drops during trnasfer
Pump automatically turns OFF
Pump Failure - Gravity feed - Nacelle drops by 22 USG (approx)
All wing tank fuel will gravity feed into the nacelle tank excepting 28 USG/188lbs CTR tank
Fuel Transfer Pumps
Transfers fuel from wing centre tanks to nacelle tanks
Transferred automatically when on AUTO and nacelle tanks down by 10 USG
The nacelle tank will fill until the fuel reaches the upper transfer limit and a float switch turns the transfer pump off
The OVERRIDE position can be used when either or both nacelle tanks float switches fail to function, this will cause the transfer pumps run continuously.
If the nacelle tanks become full, the excess fuel will be returned to the wing centre section
Fuel Gauges
The fuel gauges are located on the left side wall of the cockpit. The gauges are capable of displaying Total Fuel quantity or that or of the Nacelle tanks only
Crossfeed
This is only authorised in the event of engine failure or electric boost pump failure.
Under normal conditions it is left in the AUTO position.
This will allow automatic transfer to commence in case of engine failure on T/O when a reduction in boost pump pressure is sensed
Fuel Purge System
Pressurised air from the P3 stage of the engine compressor assembly is used to pressurise the fuel system. On engine shut down as fuel pressure reduces, this Purge system pressure pushes any remaining fuel though the manifold and injector network. This voids the engine of fuel helping to prevent Hot starts.
This purging will however cause a momentary spike in Ng during shutdown as this fuel is introduced into the combustion chamber
Boost Pumps
30 PSI - to engine pumps, reduced engine pump cavitation
Must be operable prior to T/Off
Operations not approved above A080 with boost pumps ‘INOP’
OP’s limited to 10 hrs with ‘FUEL PRESS’ annunciator on - engine pump overhauled/replaced
Siphon Break Line
Prevents fuel loss or fuel bladder collapse if the fuel cap is not properly installed
