Как предполагается заполнять надтопливное пространство азотом на протяжении всего полета? Баки дренируются забортным воздухом.
The nitrogen generation system (NGS) separates oxygen from nitrogen
from the cabin air and sends this nitrogen enriched air to the fuel tanks.
- This decreases the oxygen level in the fuel tanks.
- It makes the fuel vapor less flammable.
2. NGS makes sure the fuel tanks stay inert when the airplane is not
operational for 24 hours.
3. Air with oxygen removed is called nitrogen enriched air (NEA).
4. The NGS system has these sections:
- Generation/Storage
- Control
- Distribution
- Indication
5. The generation and storage section includes the NGS pack assembly that
makes NEA.
6. The control section includes the valves used to control the operation of the
NGS.
7. The distribution section sends the NEA to the fuel tanks.
8. The indication section includes the sensors used to monitor the operation of
the NGS and the structural thermal protection sensors used to detect overheat
conditions in the NGS pack area.
9. Control and operation of the NGS is from one copy of the NGS hosted
software application located in the general processing module (GPM) 4 in the
common core resource (CCR) cabinets.
-The NGS operates automatically with no flight deck control interface.
System Description Section (SDS)
General System Description
The inert gas system takes air from the forward cargo bay area and uses a
nitrogen generation system (NGS) to remove oxygen from this air. It then
sends nitrogen enriched air (NEA) to the fuel tanks. The NEA makes the fuel
vapor less flammable.
The NGS makes sure that the highest average oxygen concentration for the
air in the fuel tanks is less than 11.9 percent from sea level to 10,000 feet.
This highest average concentration linearly increases to 15 percent at 45,000
feet. The NGS also makes sure the fuel tanks stay inert when the airplane is
not operational for 24 hours.
The generation and storage subsystem includes the NGS pack assembly that
makes NEA. The motor driven compressor (MDC) compresses the air from the
forward cargo bay, which has heat removed by the heat exchanger before it
goes to the air separation module (ASM). The ASM makes the NEA. The flow
control valve controls the flow of the NEA to the distribution system.
The distribution subsystem sends the NEA from the ASM to the fuel tanks.
From the flow control valve, the NEA goes through a check valve with a flame
arrestor to the isolation valve. There is an isolation valve, an orifice, and a
check valve for each fuel tank to control the NEA flow. In the main fuel tanks
the NEA goes through piccolo tubes to each bay. In the center fuel tank the
NEA goes through a center tank jet pump ejector in the center tank vent
tubing.
The controlling subsystem uses the NGS function to control the valves and the
MDC to control the operation of the NGS. There is one copy of the NGS
hosted function in general processing module (GPM) 4 in the right common
computing resource (CCR) cabinet.
The indicating subsystem uses the NGS sensors to monitor the operation of
the NGS. The structural thermal protection sensors detect overheat conditions
in the NGS pack area because of an NGS pack hot air leak.
The NGS operates automatically with no flight deck control interface. Because
of this, the NGS can start without warning when power is available. The high
temperature of the NGS exhaust can cause damage to equipment and injury
to personnel.
AMM
WARNING: DO NOT BREATHE THE AIR FROM THE FUEL TANK UNTIL
YOU MAKE IT SAFE. THE NITROGEN GENERATION SYSTEM
DECREASES THE OXYGEN IN THE AIR. IF YOU BREATHE AIR THAT
DOES NOT HAVE SUFFICIENT OXYGEN, DANGEROUS HEALTH
CONDITIONS CAN QUICKLY OCCUR. DANGEROUS HEALTH
CONDITIONS INCLUDE NAUSEA, UNCONSCIOUSNESS, AND
CONVULSIONS. IF THE OXYGEN LEVEL OF THE AIR THAT YOU
BREATHE IS VERY LOW, IT CAN KILL YOU.
MMEL
The Boeing MMEL permits dispatch with the NGS system inoperative. Repairs
must be made within 10 flight days.