The fire detection card measures the average temperature of  the loops. This data goes to the AIMS through the system’s  ARINC 629 buses and is recorded by the airplane condition  monitoring function. The fire detection card monitors the two loops and their  wiring for defects. In normal (dual loop) operation, both  loops must have a fire or overheat condition to cause the  flight deck indications. If a failure occurs in a loop, the fire detection card sends the  data to the AIMS. A status message shows, and the system  changes to single-loop operation. In this mode, fire/overheat  indications occur when one loop is defective and the other  has a fire or overheat condition. The fire detection card monitors the loops for faults. In  normal (dual loop) operation, both loops must have a fire or  overheat condition to cause the flight deck indications. If one  detection loop fails, the card sends data about the failure to  the AIMS, and a status message shows. The card changes to  single-loop operation, if necessary. If both detection loops  fail, an advisory message and status messages is displayed,  and the fire detection system does not operate. Built-in test equipment (BITE) performs a test of the engine  fire detection system for these conditions: Each engine has two fire detection loops: loop 1 and loop  2. A fire detection card in the system card file monitors the  loops for fires, overheat conditions, and faults. There is a fire  detection card for each engine.  If the fire detection loops detect an overheat condition, the  fire detection card sends a signal to the AIMS and to the  warning electronics unit. The following indications occur  in the flight deck: The B777 airplane has two fire extinguishing bottles that  contain Halon fire extinguishing agent pressurized with  nitrogen. The engine fire switches in the flight deck are pulled  and rotated to release the Halon. Halon from each bottle can  be discharged to the right or left engine. Engine indicating  and crew alerting system (EICAS) messages, status messages,  and indicator lights show when the bottle pressure is low.  The two engine fire extinguishing bottles are located behind  If an engine fire occurs, the fire detection card sends a  signal to the AIMS and to the warning electronics unit, and  a warning message illuminates. The following indications  occur in the flight deck: 9-14 •  The master warning lights come on. •  An engine overheat caution message shows. •  The caution aural operates. •  The master caution lights come on. •  When the system first gets power •  After a power interrupt •  Every 5 minutes of operation  [Figures 9-20  and  9-21] •  The fuel control switch fire warning light comes on. •  The engine fire warning light comes on. •  An engine fire warning message shows. •  The fire warning aural operates. Nacelle Temperature Recording Continuous Fault Monitoring Single/Dual Loop Operation System Test Overheat Detection Boeing 777 Fire Extinguisher System Fire Extinguisher Containers Fire Detection Figure 9-19.  Components of fire extinguisher container. Mounting lugs (4) Nut Pressure gauge Bottle Packing ring Cartridge Strainer Contact assembly Gasket Discharge plug (or valve) body Swivel nut Bottle outlet