The Australian Transport Safety Bureau did not conduct an
on-scene investigation of this occurrence. The report presented
below was prepared essentially from information supplied to the
Bureau.
Aircraft arrival
At 0836 Eastern Standard Time, on 9 July 2004, after completing
a scheduled flight from Los Angeles, the Boeing 747-400 aircraft
registered VH-OEI, landed on runway 16R at Sydney airport.
Following the selection of reverse thrust, the flight crew
observed a number-2 engine fire warning message displayed on the
aircraft's primary engine indication and crew alert system (EICAS)
screen. Vacating the runway and stopping the aircraft on the
taxiway, the flight crew conducted the non-normal checklist,
discharging the number-2 engine fire extinguishers, but the fire
warning message remained. The crew then requested the attendance of
the airport rescue & fire fighting (ARFF) service.
On arrival at the aircraft, the ARFF advised the crew that there
were no signs of fire present on the engine. The crew were then
cleared to taxi the aircraft to the terminal, where ground
engineers examined the engine, again confirming that no fire was
present. On receiving that information, a normal disembarkation of
passengers and crew was carried out.
Although the fire warning message was still displayed on the
EICAS screen, a detailed inspection of the number-2 engine
confirmed that the engine had not been subjected to a fire or
overheat event. Further troubleshooting revealed the failure of an
electrical relay installed in the fire/overheat detection systems
test circuit.
Failed relay
The failed relay was installed within the fire detection `test
2' circuit and was energised whenever the FIRE/OVHT test switch was
depressed. Once energised, the contacts closed allowing power to be
provided to the automatic fire/overheat logic test system (AFOLTS)
printed circuit cards, initiating the fire/overhead detection
system test.
The internal failure of the relay led to power being supplied to
select circuits within the AFOLTS cards without depression of the
test switch. That resulted in the number-2 engine fire message
displayed on the EICAS screen.
Following the replacement of the relay, the fire/overheat
detection system was tested with no further faults found and the
aircraft was returned to service.