Fuel System Flashcards
Where is the genesis of the air for the Nitrogen Generating System for C Fuel tank?
4 pneumatic ducts
When do the C tank scavenge pumps start working?
<1200lbs
Main tanks below 50%
What powers the C tank Scavenge pumps?
Mode of flow – differential between high and low flow (high pressure to low pressure)
How many fuel pumps are there?
6 AC powered pumps (2 L + 2 R AC Fuel pumps, 2 C OVRD AC Pumps)
2 AC jettison pumps
1 DC APU pump
When does the EICAS Fuel Imbalance message display?
2000lbs +/-500lbs
How many fuel sensing probes are there, where do they send information?
1 L + 1R
2 C
Sends information to the fuel quantity processor
What are the main functions of the fuel quantity processor?
Sends adjusted fuel information (temp/density) to:
Fuel quantity indicating system
Fuel totaliser via the FMC
Fuel Configuration light
When is it acceptable to takeoff with a FUEL CONFIG light?
<5000lbs in C tank
How much fuel do we burn per hour?
10,000lbs
What does UFI stand for?
Universal Fault Interrupter circuitry
What do the UFI’s do:
Approx 1200lbs:
EICAS Advisory (L)(R) Pump pressure Low
Boeing logic DEPOWERS both C pumps off
2 Fuel pump lights
Pilots turn off pumps
L or R tank reaches 50% capacity, what happens?
High Pressure and Low pressure scavenge pumps (Not AC powered) take the remaining 1200lbs from C tank.
What do the FMC fuel totaliser and the total fuel indication on the fuel quantity indicator have in common?
the same calculation
When does the FUEL CONFIG light come on?
Fuel Imbalance 2000+/- 500
Low quantity <2200lbs in L or R tank
Turn off OVRD boost pumps with more than 1200lbs in C tanks
Why aren’t the OVRD Boost pumps on for take off with less than 5000lbs in C tank?
Abnormal delays may cause transition from C OVRD boost pumps to L/R Boost pumps during critical phase
When are the OVRD boost pumps inhibited? Why?
<50% N2
Electrical load required needs IDG to support load
In the event of an engine shut down in flight, what happens to the OVRD boost pump for that engine?
<50% N2 the pump is load shed due to loss of generator
Why is the OVRD pump inhibit removed with the refuelling door open?
Allows refuelled access to all fuel pumps
On engine start, if >50N2 and the OVRD pressure light remains on as pump is un-inhibited, what has happened?
Fuel Panel door still open, or switch fault.
Where is fuel temperature measured?
Left tank, because its coolest due to only 1 HYD fuel heat exchanger
If Calculated and totaliser fuel don’t match how do you know?
Fuel disagree message displayed on the scratch pad
When does the FMC light illuminate?
Whenever the FMC wants to tell you something, and is displaying information on the scratch pad
When does the FMC light illuminate?
Whenever the FMC wants to tell you something, and is displaying information on the scratch pad
What is the path of flow of fuel from the tank?
EEC commands fuel through the fuel metering unit.
Fuel fed from tank through:
Spar valve > 1st stage pump > 2nd stage pump > Heat Exchanger > Filter/Filter bypass > Fuel metering >Burner Can
Can you jettison to zero fuel in C tank?
Yes. UFI inhibited
When will the fuel disagree light illuminate?
> 3000lbs difference between totaliser and calculated fuel. Displayed on scratch pad
Boeing Load-shed/inhibit logic during fuel jettison is?
L3 and R3 side window heat
Inhibit calculated and totaliser comparison fuel disagree for <3000lbs
Inhibit UFI circuitry
When jettison selector moved to on, what happens?
Energising both jettison pumps
Both jettison transfer valves open
Fuel flows from centre tanks to closed jettison nozzles
In the back ground: L3 and R3 side window heat + Inhibit of FMC calculated fuel for fuel disagree for <3000lbs + Inhibit UFI circuitry
What impacts the jettison fault light?
Either jettison pumps didn’t energise (1 or both)
jettison transfer valves didn’t open (1 or both)
Jettison pump or transfer valves with fault light, does jettison have to stop?
No, valve partially open.
What is the jettison rate?
2600lbs per minute
80600lbs in half an hour
After jettison does fuel comparison and totaliser calculation return?
Yes
If the wing tanks aren’t full, what is the maximum amount of fuel you are allowed to load in to the C Fuel tank?
22,050
What depowers the C OVRD boost pumps?
Boeing logic through the UFI’s
What light does the fuel quantity processor turn on?
Fuel Configuration light
What type of heat exchangers are located in the wings?
Hydraulic
What does UFI circuitry do?
Stops fuel leaving the C fuel tank at 1200lbs
Where are the jettison nozzles located?
Inboard of the outboard ailerons
