Fuel / Oil

Question 1

Describe fuel tank arrangement:

Answer 1

12 tanks, 6 per wing; 4 main, 4 auxiliary and 4 extended range tanks

Question 2

Usable fuel capacity is?

Answer 2

48,897 gallons

Question 3

What is the purpose of the sump box in the main fuel tanks?

Answer 3

Provide uninterrupted flow of fuel to the engine during abnormal operating conditions (uncoordinated flight, gusts, sideslips, neg Gs, nose up/down attitudes) and for the outboard main tanks, to provide favorable wing loading at high speeds; contains inboard and outboard fuel tank pumps

Question 4

Any time the fuel tank pressure is greater than _____ PSI relative to ambient pressure, the primary climb valve opens to vent overboard. Any time the fuel tank pressure drops below _____ PSI, the primary dive valve opens to admit air into the tanks.

Answer 4

0.7; -0.15

Question 5

How many electrically driven fuel boost pumps per tank? Which is primary?

Answer 5

2 per tank; outboard

Question 6

What are the jettison rates for aux tanks only, ext range tanks only, aux & ext range tanks (all pumps on)?

Answer 6

ER = 5560 ppm; Aux = 5360 ppm; Both = 9000 ppm

Question 7

What is MAIN TANK LOW Caution CWA? What are the restrictions?

Answer 7

Outboard main fuel tank is less than 75% full; 280 kts or 0.825 mach (if fuel mismanagement…aka fuel remains in aux or ext range tanks)

Question 8

What is MAIN SUMP LOW Caution CWA? What are the restrictions?

Answer 8

On when fuel quantity in 1807 lb capacity sump of each outboard main tank (1 or 4) drops below 1600 lbs (warns of possible adverse wing loading); 280kts/0.825 M

Question 9

What is a VENT FILL light (on FE fuel panel)?

Answer 9

Vent box is about 1/3 full (float switch in vent box closes) Each vent system is terminated at a vent sump in outboard main tanks. A VENT FILL indication will be caused by a faulty main tank fill valve or a faulty auxiliary or extended range refuel valve OR could be a broken heat exchanger or liquid nitrogen pressurization line in the outboard main fuel tank.

Question 10

How does the Fuel Tank Pressurization system work?

Answer 10

 The fuel tanks are pressurized automatically whenever the dewars contain liquid nitrogen at the correct saturation pressure and the isolation valves are open.
 Pressure in the fuel tanks is controlled by pressure regulators which maintain a positive pressure and by vent valves which prevent overpressure or underpressure within the preset limits of − 0.35 to 1.5 PSI.
 The vent valve assembly consists of a primary and a secondary climb and dive valve.
 The primary climb valve opens automatically to vent the fuel tanks at 0.7 to 1.0 PSI because of increased nitrogen pressure, atmospheric pressure drop, or airplane climb to a higher altitude.
 The primary dive valve opens at - 0.15 to - 0.25 PSI to admit air to relieve fuel tank pressure decrease due to lack of nitrogen, or rapid descent of the airplane.
 If the primary climb or dive valve fails to open, the secondary climb valve will open automatically to vent the fuel tanks at 1.0 to 1.5 PSI, or the secondary dive valve will open automatically at - 0.25 to - 0.35 PSI to admit air.
 Additionally, in the event the secondary climb and dive valve fails to open, it can be manually controlled to open both the climb and dive poppets to relieve any overpressure or underpressure when indicated by the fuel tank pressure warning lights on the flight engineer panel.

Question 11

For fuel tank pressurization, primary regulators maintain a pressure of: (by regulating flow of nitrogen from dewars into fuel tanks)

Answer 11

0.3 to 0.5 psi

Question 12

For fuel tank pressurization, secondary regulators maintain a pressure of: (1.19.4.2) (by regulating flow of nitrogen from the other dewar into fuel tanks)

Answer 12

0.0 to 0.3 psi

Question 13

The primary climb valve opens automatically to vent fuel tanks at 0.7 to 1.0 psi due to:

Answer 13

Increasing N2 pressure, atmospheric drop or climb to higher altitude

Question 14

The primary dive valve opens automatically at -0.15 to -0.25 psi to relieve tank pressure due to:

Answer 14

Lack of N2 or rapid descent

Question 15

Describe what happens if the primary climb or dive valves fail to open:

Answer 15

The secondary climb valve will automatically open to vent at 1.0 to 1.5 psi; the secondary dive valve will auto open at -0.25 to -0.35 to admit air

Question 16

What if the secondary climb or dive valve fails to open?

Answer 16

It can be manually controlled to open using the climb and dive “poppets” (Vent Valve push buttons)

Question 17

What hydraulic system powers the Secondary Climb and Dive valves?

Answer 17

Hydraulic system #1

Question 18

What does pushing the LEFT WING or RIGHT WING (VENT VALVE) pushbuttons do?

Answer 18

Manually opens secondary climb/dive valves and fuel tanks for affected wing are vented to atmospheric pressure) (should get VENT OPEN indication) & closes both liquid nitrogen isolation valves (NOTE: pushing the button again will reset the climb and dive valves and open both nitrogen isolation valves.)

Question 19

When does the WING PRESSURE WARNING (CWA) & FUEL TANK PRESSURE WARNING (FE FSS Panel) light come on?

Answer 19

If tank pressure greater than 2.0 psi or less than - 0.7 psi

Question 20

What is the problem when you get a FUEL TANK PRESSURE WARNING? What should you do?

Answer 20

Primary and secondary climb/dive valves have failed to equalize the pressure between the ambient air and fuel tanks. If the corresponding VENT OPEN light does not come on and the fuel tank pressure warning does not go off, discontinue a climb or descent. Jettison as a last result (no ref).

Question 21

What is fuel scrubbing and how does it work?

Answer 21

 Reduces O2 in fuel; it is done in each tank during ground and air refueling; an aspirator draws N2 from the ullage and mixes it with fuel; fuel entering tanks is about 5% O2; ullage stays < 9% O2
 The decrease of atmospheric pressure during climb causes the fuel to release a flammable gas which then mixes with the vapors already in the ullage.
 The scrubbing subsystem of the Fire Suppression System (FSS) scrubs or reduces the oxygen dissolved in the fuel.
 This prevents the release of non-inert (flammable) gas from the fuel thus destroying the inert atmosphere in the fuel tanks.
 Fuel scrubbing is accomplished in each tank during ground and air refueling by an aspiscrubbing function.
 The aspiscrubbing function scrubs the fuel to such a low level of oxygen concentration that no additional scrubbing is required during climb.

Question 22

Does the C-5M have a controllable fuel heater system?

Answer 22

No, the fuel is automatically heated in a main fuel/oil heat exchanger prior to the fuel filter and a IDG fuel-oil heat exchanger downstream.

Question 23

How does the C-5M inform aircrew that an engine filter is clogged and the fuel filter bypass valve is open?

Answer 23

EDS will send generate a TLD Level A and a subsequent ENG CONTROL FAULT Advisory

Question 24

What does the PRESS LOW light indicate?

Answer 24

Tank fuel boost pump failure (if outboard fails, turn on corresponding inboard pump) If both fail in a main tank, see Section 3 procedures

Question 25

What is the indication and corrective action for a tank boost pump failure?

Answer 25

 PRESS LOW light on FE Fuel Panel
 If the outboard boost pump (primary pump) in any tank fails, turn on the inboard boost pump and place the outboard boost pump switch in the OFF position.
 If both pumps fail, then the engine will suction feed

Question 26

What are the suction feed limits?

Answer 26

 JP8: Climb Outboard - 32,000 ft Inboard - 40,000 ft
 JP4: Climb Outboard - 16,000 ft Inboard - 20,000 ft
 Cruise: no suction feed limits for non-maneuvering cruise

Question 27

Heavyweight is defined as gross weights above ____ pounds.

Answer 27

635,850

Question 28

What is the maximum fuel load of the C-5?

Answer 28

332,500 lbs