The fire extinguishing system provides the operator with a means of combating fires in both the engines and the APU from the cockpit. The system provides complete redundancy in all its critical functions. The fire extinguishing system has containers to hold the fire extinguishing agent and has the applicable components to send the agent to the correct location.

Two fire extinguisher bottles are installed in the rear of the aft equipment bay. These bottles can be discharged into any combination of engines/APU.

On the overhead fire control panel, a pull-and-turn type of Fire Control Handle is provided for each engine and the APU. Each handle has an integral three-position rotary switch for bottle selection.

If there is a fire in one of the engines or the APU, a signal goes to the fire detection and extinguishing control unit. The control unit sends a warning to the engine indication and crew alerting system (EICAS) and to the applicable fire handle in the flight compartment. There is also an aural warning. The fire handle is pulled out to arm the system. Then the handle is turned clockwise or counterclockwise to release the agent to the required location.

The fire detection and extinguishing control unit (FIDEEX CU) is the same computer used in the fire extinguishing system for control, monitoring, test, and fault or failure recording. Failure recording is retrievable for troubleshooting using the PMAT. The FIDEEX CU also provides CAS messages applicable to the fire extinguishing system.

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Two stainless steel fire extinguishant containers or bottles are mounted side by side in the rear of the aft equipment bay. The forward bottle is Bottle No. 1 and the rear one is Bottle No. 2.

Each bottle has three ports, and each port is fitted with a discharge head and associated plumbing to allow extinguishant from that port to flow into either engine or the APU. Each head comprises a cartridge containing two bridge wires.

A burst disc which is part of each discharge head has two functions:

• To rupture when the associated squib is "fired" electrically from the cockpit, and allow the extinguishant to flow freely to the assigned area.
  
  
• When the temperature of an extinguisher bottle rises above the preset thermal relief limit, one or more of its discs will rupture in no specific sequence to preclude the explosion/bursting of the bottle itself. In such a case, the extinguishant from that bottle will be discharged into the corresponding engine(s) and/or APU compartment.

The extinguishant is an inert gas (Halon 1301). It does not cause any damage or corrosion if it escapes into an operating engine or APU.

A direct reading pressure gauge (also called "alarm gauge") is provided on each fire extinguisher bottle and displays the charge level of that bottle. A pressure switch is installed under the gauge of each bottle.

If a bottle's pressure drops below 250 ± 25 psig, the respective pressure switch signals the FIDEEX CU, which will initiate a display of the associated amber CAS caution message of FIRE BTL 1/2 LO PRESS.

Each bottle contains 6.5 lbs of Halon 1301 and has the following features:

Nominal pressure, 600 (+ 25, − 0) psig at 21 °C (70 °F), Safety Relief pressure, 1,800 (± 100) psig.

For information regarding bottle weight Time Limits Maintenance Checks (TLMC), select Troubleshooting Tips from ATA 26-00-00 Fire Protection System Description main page.

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A squib located at each discharge port, contains a small explosive charge in its main chamber and two bridgewires. Each charge is capable of "firing" the squib if the appropriate current is passed through it.

The electrical power for the squib comes from two 28 VDC sources through the control unit. After a squib is fired, the applicable container will release all of its agent into the selected zone.

Each squib's electrical cable is tied and clamped so that it can only be physically mated with the its associated squib. This prevents cross-wiring of the cables. The chamber in the squib is sealed by a flat-plate attached to a "dagger".

The sharp end of the dagger is aimed at the burst disc that is located in the squib discharge pipeline. When a fire handle is rotated to either discharge position, an electric current of 5 amperes is sent through both the bridgewires of a specific squib.

Even if one bridgewire malfunctions, the charge will explode with the remaining bridgewire and the dagger will rupture the burst disc, thus discharging the fire extinguisher bottle.

A continuous 1 ampere current is sent through each of the bridgewires in each squib continuous monitoring by the FIDEEX CU. If a bridgewire fails the continuity check, the FIDEEX CU will log a fault code in it NVM.

The control unit monitors the resistance of the two wires in each squib. If only one of the bridgewires fails the test, the FIDEEX CU merely records it in its NVM. If the second wire also fails in the same squib, the CU will initiate the display of any one of the following CAS (cyan) advisory messages as applicable:

• L ENG SQUIB 1 FAIL
• R ENG SQUIB 1 FAIL
• APU SQUIB 1 FAIL
• L ENG SQUIB 2 FAIL
• R ENG SQUIB 2 FAIL
• APU SQUIB 2 FAIL

When a bottle is discharged into an engine or the APU, the respective low bottle pressure message confirms that the correct bottle has been discharged into the specific area that was targeted.

Warning:
After maintenance work on the fire extinguisher bottles or squibs, ensure that each cable is properly oriented to its specific squib on the correct bottle number, in order to avoid discharge into the wrong area in a real emergency.

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There are three fire handles installed on the fire extinguishing panel in the flight compartment, one for each of the engines and one for the APU. Each fire handle has a light which comes on when a fire is detected. To prevent an accidental engine/APU shutdown and fire extinguisher discharges, each fire handle is maintained in the stowed position by four center springs and a solenoid operated switch. When a fire warning is received, the data acquisition unit unlocks the solenoid to allow ease of pulling the handle. The EICAS causes the light in the applicable fire handle to come on. To perform a precautionary engine/APU shutdown (no fire condition), the handle must be manually released by depressing the manual override button. When the pilot pulls out the fire handle to arm the system, the following occurs:

• The squibs for the applicable engine on both containers are grounded
• The applicable generators are de-energized
• The fuel shutoff valves for the applicable engine or APU is closed
• The firewall hydraulic shutoff-valve for the applicable engine is closed
• The bleed management system stops the bleed air from the applicable engine or APU

To discharge an engine bottle, the fire handle is rotated counterclockwise and held at least one second so the applicable squib on container 1 will get power. If the fire handle is rotated counterclockwise the applicable squib on container 1 will get power. If the fire handle is rotated clockwise the applicable squib on container 2 will get power. When the squib gets power an explosion in the discharge head of the container will break a disk assembly to let the extinguishing agent into the discharge lines.

To discharge the APU bottle, the fire handle is rotated counterclockwise and held at least one second so the applicable squib on container 1 will get power. To discharge the second bottle in the APU, the lock release pin must be slid to the opposite position to allow the handle to be rotated past the center position.

Three T-shaped pull-and-turn type fire control handles are installed on the overhead panel in the cockpit. The left and right handles are for fighting fire in the respective engines. The center handle is for the APU.

Each fire control handle has a large red integrally illuminated L (left), APU, and R (right) inscribed on the left, middle, and right handles respectively. Each lamp is illuminated when the associated fire warnings are triggered and will not be extinguished unless the respective fire condition has been resolved.

Behind the fire control panel and hidden away from view in the cockpit, is a solenoid controlled lock mechanism for each fire control handle which acts as a safety device for its handle. Each fire handle is maintained in the stowed position by four center springs and a solenoid operated switch.

Each lock prevents the respective handle from being pulled out inadvertently, when there is no fire in the associated engine or the APU.

When the FIDEEX CU detects a fire, the data acquisition unit energizes the respective solenoid releasing its lock mechanism. With the lock released, the associated fire control handle can be pulled out without resistance.

At the bottom of each fire control handle is a button which, when pushed and held, mechanically releases the respective lock, permitting the handle to be pulled out even when no fire is detected by the FIDEEX CU. This feature is provided for over-riding the lock mechanism if an operator needs to pull out the fire control handle intentionally, when there is no fire in the respective engine/APU, or in case the lock release solenoid fails during an actual fire condition.

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The engine discharge lines come from each container and connect to a check valve to become one discharge line that goes to the engine nacelle (at approximately FS945). Connected at this point, are lines that go to three areas of the engine: one each goes to zone 1 at the forward and aft end of the electronic engine controller (EEC) and a third one goes to zone 2 at the bottom of the engine. The two outlets at zone 1 have two outlets each.

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The APU discharge lines come from each container and connect to a check valve to become one discharge line that goes through the firewall. On the other side of the firewall, the discharge line becomes two again, where one goes to the front of the APU (fuel and oil systems components) and one goes to the right side (combustor area).

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The discharge check valves prevent the extinguishing agent from going from one container to the other container when the fire extinguishing agent of a container is released.

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Engine Fire Control

Pulling an engine fire control handle will send an output to the FIDEEX CU which will initiate a signal:

• To close the "firewall" fuel SOV of that engine
• Cause the BMC (Bleed Management Computer of the pneumatic system) to close the bleed air supply SOVs from that engine
• Cause the electrical system to trip the generators of that engine
• Cause the hydraulic system to close the fluid SOV of the EDP of that engine
• To arm the applicable circuits of the fire extinguishing bottles, and
• Cause the FMQGC to permit pressure defueling of the aircraft

The hand-grip can be turned to the left or right (counter clockwise towards No. 1 position, or clockwise towards No. 2 position) only if the hand-grip has been pulled out from the panel.

When an engine fire control handle is first pulled and then turned momentarily to the No. 1 or No. 2 position, it will discharge the fire extinguisher designated as No. 1 or No. 2 respectively into the selected engine. There is no preferred sequence in discharging the two bottles; either bottle may be discharged first.

When one of the two fire extinguishers has been discharged into an engine, the hand-grip must be moved to the middle, so as to return it to its normal position; alternately, the handle can be turned past the mid-position to the other position momentarily, to discharge the second fire extinguisher into the same engine.

Note that after the first extinguisher has been discharged into an engine for a fire, the firewire takes about 30 - 40 seconds to cool down and cancel the warnings.

Warning:
To avoid prematurely discharging the second fire bottle into an engine/the APU when such a discharge is not required, especially in flight, wait a minimum of 40 seconds and confirm that the warnings are present before selecting the second bottle into that area.

APU Fire Control

Under most circumstances, a single fire extinguisher is adequate to extinguish a fire in the APU. To remind the operator to conserve the contents of the second fire extinguisher (in case it should be required for an engine fire later on), the APU fire control handle is provided with a small two position lock-lever fitted close to the right hand side of the base of the control handle shaft.

The action needed to discharge the first fire extinguisher into the APU compartment is identical to that used on the engines. A difference with the APU handle is the lock lever prevents the operator from accidentally moving the hand-grip past the center position and thus discharging a second fire extinguisher unintentionally.

For discharging a second fire extinguisher into the APU compartment, the lock lever must be moved to the right, (away from the shaft of the fire control handle) while the hand-grip is turned at the same time. Without such a selection on the lock lever, the hand-grip will be mechanically prevented from turning and the bottle can not be discharged.

Pulling the APU fire handle will send an output to the FIDEEX CU which will initiate a signal to:

• The APU FADEC to close the solenoid SOV at the APU's FCU
• The FMQGC (fuel system computer) to close the (firewall) fuel SOV of the APU
• The electrical system to trip the APU generator
• The APU FADEC to close the LCV/Load Control Valve, and
• Arm the applicable firing circuits of the fire extinguishing bottles

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The FIDEEX CU has two independent channels. The fire protection system, in conjunction with the FIDEEX CU, provides the following functions:

• Receives and distributes electrical power from redundant 28 VDC power supply lines connected to the aircraft battery bus and SSPC in the SPDA
  
  
• Monitors and tests the fire detection loops of the engines and the APU for fire, open/short circuits and cross-wired detection loops
  
  
• Monitors and tests the overheat detection loops of the MLG bays for overheat and shorts/ open circuits ensuring that Channel A detection logic is used for left main wheel well loop and Channel B logic, for the right wheel well loop
  
  
• Performs internal and operator-initiated BITs (built-in tests) and reports all pertinent details of health and status to EICAS/CAIMS as applicable

Cold Start Power-On BIT

The test named above is performed by the FIDEEX CU, upon application of power to the aircraft battery bus (SPDA No. 2), after power outages of longer than 200 milliseconds, and comprises the following:

• Initialization of the microprocessor
• RAM and ROM memory checks of the microprocessor
• A check for cross-wiring of the A and B fire detection loops, and
• A periodic BIT and other subsystem checks

Warm Start Power-On BIT

To perform this test, the must sense a power interruption of between 5 and 200 ms. This test consists of:

• Initialization of the microprocessor, and
• A periodic BIT and other subsystem checks

Periodic BIT

During normal operation and CAIMS standby mode, the FIDEEX CU performs the periodic BIT once every five minutes. This consists of the following testing:

• Detector loops for open circuits
• Detector loops for continuity
• If a loop fails a fire test, test the loop monitoring and detection circuitry, and
• Test of fire and overheat warning discrete output drivers

Normal Continuous Operation

After power-up processing is complete, the FIDEEX CU will enter an operating mode of continuous detection and monitoring and Periodic BIT. The following are monitored on a continuous basis during this phase:

• System Fire Status
• Loop Fault Status (Shorts/Open)
• Fire/Smoke Detection circuits
• Smoke Detector Alarm and Operational Status
• Discrete Output Driver Status
• Bottle Pressure Status
• Bottle Power
• Bridgewire (fuse wire) Continuity in the Discharge Squibs

Note:
The FIDEEX CU will not display any CAS messages in the event of a single bridgewire failure in one or more squibs; however, the malfunction will be recorded in the NVM (Non-Volatile Memory) to be retrieved via the CAIMS PMAT at a later stage, for example, during scheduled/random checks.

System Fault Recording / CAIMS Interface

The FIDEEX CU is capable of reporting all faults recorded and stored by it via the ARINC data bus to the Fault Warning Computer (FWC) in the Integrated Avionics Computer (IAC).

The FIDEEX CU can record up to 16 of the most recent ground/flight faults in its NVM.

The system will be capable of recording and storing sufficient fault details to facilitate identification of the failed LRUs, and line maintenance.

The system will keep track of repeated occurrences of the same fault within the same flight leg by incrementing a fault counter up to a maximum of 4 faults per flight.

During CAIMS mode, the FIDEEX CU will offer full functional support for CAIMS system flight faults summary.

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Operator Initiated BIT

CAIMS may be used for FIDEEX initiated BIT.This test is similar to the pilot-initiated test performed from the EMS CDU. The LRU TEST menu allows INIT BIT selection.

• DAU 3 must be operational for the smoke detection part of the test to be successful
• Functions activated by this test
  

  • Verifies fire detection capability of the left engine, right engine, APU and the left and right MLG bay
  • Sets the smoke detectors (if installed) into the alarm mode during the test

• Physical effects to look for are
  

  • Fire lights of each serviceable fire detection zone are illuminated for 10 seconds
  • Aural warnings of the various fire/overheat/smoke detection are heard in sequence during the test

The testing action is started by selecting CONFIRM. This activates a number countdown from 30 seconds, down to 0, and the text PASSED/FAILED as applicable.

Active and Stored Faults

Active and stored faults including pertinent details in each case are accessed by following routine navigation procedures through the CAIMS.

The FIDEEX is capable of reporting and storing faults. The FIDEEX can record up to 16 of the most recent ground/flight faults in its NVM. The system can record and store sufficient fault details to easily identify the failed LRUs.

The system keeps track of repeated occurrences of the same fault within the same flight leg by incrementing a fault counter up to a maximum of four faults/flight. During CAIMS mode, the FIDEEX offers full functional support for CAIMS system flight faults summary.

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Component Location Index
IDENT	DESCRIPTION	LOCATION	IPC REF
A111/A112	FIRE EXTINGUISHER CONTAINERS	ZONE(S) 331	26-21-01 [ GX ] [ GXRS ] [ G5000 ]
-	DISCHARGE CARTRIDGES	ZONE(S) 331	26-21-05 [ GX ] [ GXRS ] [ G5000 ]
A209/A210/A211	FIRE HANDLES	ZONE(S) 221/212	26-21-13 [ GX ] [ GXRS ] [ G5000 ]
-	ENGINE DISCHARGE LINES	ZONE(S) 331/332/412/422/432/442	26-21-21 [ GX ] [ GXRS ] [ G5000 ]
-	APU DISCHARGE LINES	ZONE(S) 331/332/321/322	26-21-29 [ GX ] [ GXRS ] [ G5000 ]
-	DISCHARGE CHECK VALVE	ZONE(S) 331	26-21-45 [ GX ] [ GXRS ] [ G5000 ]

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