Fairchild Industries Inc SA227-AC, VH-CUZ

The aircrew's decision not to activate the fire extinguisher was not in accordance with the requirements of the operator's approved phase-one emergency checklist procedures. Those procedures are immediate actions, and the operations manual does not suggest that the memory items from an emergency checklist are optional, or that they should not be completed in certain circumstances once they have been commenced.

As the PIC had recently experienced two similar engine fire indications in this aircraft, his response on this occasion may have been influenced by those recent events. However, the PIC's decision not to activate the fire extinguisher placed heavy reliance on the extinguished fire-warning lights as an indicator that there was no longer a threat of fire. That decision, whilst supported by the company's chief pilot, did not appear to take into account the possibility that a malfunction of the fire-warning system was masking a real fire.

When the SA227 Metro aircraft was turning onto the downwind leg
of the circuit, the crew noticed that the left-engine fire warning
annunciator light was illuminated. The phase-one emergency
procedures were immediately initiated. Those procedures included
immediate recall and checklist prompted actions. Accordingly, the
engine was shut down. Shortly after, the fire warning light
extinguished. The pilot in command (PIC) then decided not to
activate the fire bottle. A single-engine approach and landing was
conducted.

This was the third left-engine fire indication the aircraft had
experienced since September 1999, the previous two having occurred
over a two-week period. The PIC was involved in all three events.
During the first and second events, the fire warning indications
had remained illuminated following engine shutdown, and the PIC had
discharged the corresponding fire extinguisher into the engine fire
zone on both those occasions. However, the PIC chose not to
discharge the fire extinguisher during the most recent event as the
fire-warning indications had extinguished following the engine
shutdown. The company's chief pilot supported that decision.

Following the first event, maintenance investigation carried out
by the operator revealed that the insulation on a wire in the
fire-warning system wiring harness had chafed through while in
contact with a nearby bracket. That damage was rectified. After the
second event, the fire-detection system was checked for operation.
No fault that could have contributed to the activation of the
fire-warning system was found. Notwithstanding, it was considered
that the lower-turbine fire detector was possibly too close to the
engine, and may have resulted in a spurious fire indication. The
detector was re-positioned and the aircraft returned to
service.

Investigation of the most recent event showed that one of the
fire detectors was activating at an incorrect temperature. The
aircraft was returned to service following replacement of that
detector with one capable of activating within the correct
temperature range. At the time of writing this report, similar
problems had not re-occurred.

The phase-one emergency checks are described in detail in the
operator's aircraft flight operations manual and in the aircraft
flight manual. The immediate recall actions require that the engine
be shut down with the "stop and feather" control, and that the fuel
and hydraulic oil be isolated, before the fire extinguishing system
is discharged. The procedure is to then be continued from a written
checklist. Items identified as recall actions are intended as a
non-discretionary response to a fire warning.