LOWER-CARGO FIRE EXTINGUISHING -
DESCRIPTION AND OPERATION
1. General
A. The lower-cargo fire extinguishing system includes:
The CARGO FIRE panel
The miscellaneous system controller
The systems control panel
The engine alert display
The system display air page
The fire extinguishing containers
The discharge cartridges
The deployment lines
The low-pressure system.
2. Cargo Fire Panel
A. The CARGO FIRE panel has the pushbutton switchlights that control the lower-cargo compartment
fire extinguishing and ventilation systems. The switchlights have spring-loaded clear plastic guards
to make sure they are not pushed in error. These are off - momentary on switches. The switchlights
have two parts that are lighted separately. The switchlights are:
The AGENT DISCH FWD1/LOW switchlight
The AGENT DISCH FWD2/LOW switchlight
The AGENT DISCH AFT1/LOW switchlight
The AGENT DISCH AFT2/LOW switchlight.
B. The FWD1 (or FWD2 or AFT1 or AFT2, as applicable) part of the switchlight comes on, when the flight
crew pushes on the switchlight. This is done to release the FIREX agent. After the FIREX agent is
released, the LOW part of the switchlight comes on. The LOW part come on when the FIREX
container pressure is less than the specified value. This tells the flight crew that the FIREX agent is
released. The FWD2 (or AFT2) switchlights are used if the fire stays and a second release of FIREX
agent is necessary.
C. The CARGO FIRE panel has warning lights (FWD HEAT/SMOKE and AFT HEAT/SMOKE) to show
heat and smoke conditions. There are also FWD FLOW DISAG/OFF AND AFT FLOW DISAG/OFF
indicator light. The OFF part shows that the cargo ventilation fan is off. The DISAG part illuminates
when the air flow disagrees with the switch position.
D. The MANUAL TEST/TEST push-button switchlight on the CARGO FIRE panel lets you test the
detection system components. This is to make sure they are in satisfactory condition. This switchlight
is used to test both the lower-main-deck cargo and deck cargo compartment components.
3. Miscellaneous System Controller
A. The miscellaneous systems controller (MSC) contains the circuitry to make the CARGO FIRE panel
switchlights come on. The fire extinguishing system switchlights that come on are:
The FWD1 part of the AGENT DISCH FWD1 switchlight
The FWD2 part of the AGENT DISCH FWD2 switchlight
The AFT1 part of the AGENT DISCH AFT1 switchlight
The AFT2 part of the AGENT DISCH AFT2 switchlight.
B. Usually the FWD1 (or AFT1) light comes on first. Then the FWD2 (or AFT2) light comes on 90 minutes
after container No. 1 is discharged, if the fire stayed.
C. The FWD1 (or AFT 1) logic circuit makes the light:
Flash (2Hz rate) if the CPU is good, the fire container No. 1 pressure is good and a fire is found.
D. The FWD2 (or AFT2) logic circuit makes the light:
Come on steady, if the CPU has failed and a fire is found
Flash (2Hz rate) if the CPU is good, fire container No. 2 pressure is good, a fire is found and one of
these occur
Fire container No. 1 pressure is not good (low-pressure) and the container has not been operated
The 90-minute timer has expired.
E. The MSC also has a 90-minute counter that sends data to the DEUs, after fire bottle 1 is operated. The
DEUs make a 90--minute countdown display.
4. Systems Control Panel
A. The systems control panel is used to show the flight crew the status of the MD-11 operating systems.
To get the system display air page the flight crew pushes the AIR push-button switchlight. When
pushed the switchlight comes on and shows that the system display air page is on. The system
display air page shows the flight crew the status of the environmental system of the aircraft.
5. Engine Alert Display
A. The engine alert display shows the flight crew the status of the engine parameters. It shows also all
alert signals. When the CRG FIRE LWR FWD (or CRG FIRE LWR AFT) appears a SMOKE alert
message appears, the flight crew pushes the AIR push button switchlight. The system display AIR
page appears.
6. System Display Air Page
A. The system display AIR page shows the flight crew the status of the environmental system of the
aircraft. It also shows them alert messages and consequence messages. When the alert message
CRG FIRE LWR FWD or CRG FIRE LWR AFT appears, a consequence message LAND AT NEAREST
SUITABLE AIRPORT also appears. If a fire occurs in the cargo area the display shows which detector
supplied the warning.
7. Lower-Cargo FIREX Containers
A. The lower-cargo compartment FIREX containers are in the center accessory compartment. The
FIREX containers are hermetically sealed, stainless steel spheres that keep the bromotrifluoromethane
(CF3GR) FIREX agent.
NOTE: The FIREX containers are not designed to be filled and pressurized while installed in the
aircraft. A low--pressure or empty FIREX container must be replaced with a full FIREX
container.
B. Each container has two agent discharge heads that includes the debris screens, explosive cartridges
and flow channels. The discharge head also operates as an adapter for the deployment lines. The
cartridge is an electrically fired, explosive device that supplies the force to break the frangible disc.
This releases the FIREX agent into the forward-cargo or to the center/aft-cargo compartments.
C. The low-pressure switch on the FIREX container is part of the low-pressure warning system. The lowpressure
switch is installed as an internal part of the container. The switch low pressure is set to
close if the pressure drops to approximately 70 psi (482.7 kPa) maximum. The switch then operates
the AGENT LOW light in the flight compartment.
D. The FIREX containers have a frangible disc welded to the discharge port. The pressure relief device
is the frangible disc-type installed with the discharge port. The pressure relief device will blow at an
internal pressure of 1200--1400 psi (8274-9653 kPa).
8. Discharge Cartridges
A. The source of power for the cargo FIREX system is the battery bus. The bus supplies 28VDC through
10-ampere circuit breakers to the system control switches. There is one circuit breaker for cargo
FIREX container No. 1 and one for cargo FIREX container No. 2.
B. Each FIREX container has two discharges cartridges. Each discharge cartridge contains two squibs
(powder charges) that are fired electrically. An electrical element in each squib heats the powder to
ignition. Both electrical elements operate simultaneously when electrical current is supplied.
However, either electrical element can fire the cartridge. The cartridges control the release of the
cargo FIREX agent to the forward and center/aft-compartments, as necessary. The four AGENT
DISCH pushbutton switchlights on the CARGO FIRE panel operate the cartridges independently.
C. There is one low-pressure switch in each FIREX container. The output of the switch makes the LOW
light in the correct switchlight come on. This occurs when the FIREX container pressure is less than
the specified value.
9. FIREX Deployment Lines
A. The FIREX deployment lines transmit the FIREX agent from the FIREX container to the fire zone
location. The deployment lines are made of metal tubing. The forward-cargo compartment has one
deployment line to release the FIREX agent from one of the two lower-cargo FIREX containers. The
center/aft-cargo compartment also gets the FIREX agent from one of two of the lower-cargo
compartment FIREX containers.
B. The lower-cargo compartment deployment lines stop at eight nozzles. Four nozzles are located in
the forward-cargo compartment ceiling adjacent to the smoke detectors. Four nozzles are located in
the center/aft-cargo compartment adjacent to the smoke detectors in the ceiling of that compartment.
10. Low-Pressure Warning System
A. Four amber agent low lights (AGENT DISCH FWD 1/LOW and FWD 2/LOW, and AGENT DISCH AFT 1/
LOW and AFT 2/LOW) are located on the overhead CARGO FIRE panel. These are push-button
switch lights. The LOW part of the push-button switchlight tells of a low-pressure or empty FIREX
container. The LOW part of the push-button switchlight is operated by the low-pressure switch on the
FIREX container.
B. The low-pressure switch is set to close at 70 (+10) psi. When the switch closes, it supplies a ground
to the electrical circuit. This causes the amber LOW (or FWD 2/LOW or AFT or AFT 2/LOW, as
applicable) light portion of the FWD 1/LOW indicator light to come on. The FWD 1/LOW indicator light
is installed on the overhead CARGO FIRE panel.
11. System Operation
A. Lower-cargo compartment FIREX operation is done with the CARGO FIRE panel. When a lowercargo
compartment fire is detected in:
(1) The forward-cargo compartment:
You lift the AGENT DISCH FWD 1/LOW push-button switch light guard
Push the switchlight (this supplies ignition for the discharge cartridge of FIREX container No.
1)
If a second FIREX agent release is necessary, you lift the AGENT DISCH FWD 2/LOW pushbutton
switch light guard
Push the switchlight (this supplies ignition for the discharge cartridge of FIREX container No.
2).
(2) The center/aft-cargo compartment:
You lift the AGENT DISCH AFT 1/LOW pushbutton switchlight guard
Push the switchlight (this supplies ignition for the discharge cartridge of FIREX container No.
1)
If a second agent release is necessary, you lift the AGENT DISCH AFT 2/LOW pushbutton
switchlight guard
Push the switchlight (this supplies ignition for the discharge cartridge of FIREX container No.