On 3 September 2017, a Fairchild SA227-AC aircraft, registered VH-SEZ, was operating Sharp Airlines flight SH843 from Portland to Essendon, Victoria. The first officer was pilot flying (PF) and the captain was pilot monitoring (PM).
About 46 NM east of Portland, overhead Warrnambool, and in the cruise at flight level (FL) 170, the left engine fire warning lights on the annunciator and fire warning panels started to momentarily illuminate. At 1608 Eastern Standard Time, the flight crew contacted air traffic control (ATC) advising that they required a clearance to descend to 9,000 ft and that they would require a direct track to Essendon.
The fire warning lights continued to flicker and then both remained illuminated. As a result, the flight crew assessed that there was an engine fire. They conducted the memory checklist for in‑flight engine fire, which included:
- shutting down the left engine
- feathering the left propeller
- shutting off the left fuel supply and hydraulic system
- discharging the fire retardant.
The fire warning lights then extinguished.
The captain looked over his left shoulder at the left engine and could not see any smoke, flames or scorch marks. The flight crew then declared a MAYDAY to ATC, and reported that they had experienced an engine fire and that the fire was extinguished.
The captain made a public address to the passengers, explaining that they had shut down the left engine due to suspected fire and asking any passengers who had seen smoke or flames to come forward and let him know. No one reported any visual indication of fire.
The flight crew assessed their options for landing, considering both Warrnambool and Avalon Airports. Although they were nearer to Warrnambool Airport, the runway there was shorter and narrower and the wind was gusty, so the crew elected to divert to Avalon Airport. The flight crew reported that a tailwind en route to Avalon and the presence of emergency services also influenced their decision.
At 1613, the flight crew advised ATC that they required direct tracking to Avalon Airport. They received a clearance to do so.
As the aircraft tracked to Avalon, and about 5 minutes after the fire warning lights had extinguished, the lights started to flicker and then came back on to a steady warning. By that time, the crew had tested the integrity of the fire warning loop, discharged the bottle of fire retardant and shut down and secured the left engine.
ATC advised the crew that Runway 36 at Avalon had an occasional 5 kt tailwind and Runway 18 had an occasional tailwind of 9 kt. The flight crew responded that they would require Runway 36. When the aircraft was about 15 NM from Avalon, the captain took over the pilot flying role. ATC provided heading guidance to the flight crew, and the aircraft landed at Avalon at about 1626.
After landing, firefighters advised that there was no sign of fire in the engine. Consequently, there was no need to conduct an emergency evacuation and the passengers and crew disembarked normally.
Engineering examination did not identify any signs of fire, smoke or heat damage in the left engine bay. Engineers inspected the four left engine fire sensor probes and all appeared to be functioning normally, but they replaced the lower rear sensor due to cracking of the ceramic insulator.
On the fire extinguisher control panel, each engine has a button and a tri-coloured light – red for fire, green to indicate system integrity of the fire loop, and yellow to indicate a bottle of fire retardant had been discharged and was empty. After the crew pressed the fire button, the empty (yellow) light did not illuminate. This was despite the fact that the fire bottle pressure gauge was indicating zero, after being full pre-flight, and there was indication of discharge into the engine. The yellow light did illuminate when the bulb was tested however, which indicated an issue with the circuit.
Engineers found that the logic control unit in the fire extinguisher control assembly had failed, resulting in erroneous illumination of the engine fire warning. The logic module was replaced, along with the fire extinguisher control panel.
Approach and landing
The captain commented that two out of their six cyclic biannual simulator checks included fire warnings, engine shutdowns and single engine actions. In this occurrence, the engine shutdown, diversion and single-engine approach and landing were consistent with the simulator training. There were no issues with controlling the aircraft or with its performance.
These findings should not be read as apportioning blame or liability to any particular organisation or individual.
- The fire extinguisher control logic module failed, resulting in an erroneous engine fire warning.
This incident highlights the importance of well-designed simulator training and robust threat and error management procedures. The captain commented that it was important to treat fire warnings as legitimate indications of fire. Additionally, the declaration of an emergency alerts air traffic control and enables the provision of appropriate assistance.
- Pilot Flying (PF) and Pilot Monitoring (PM): procedurally assigned roles with specifically assigned duties at specific stages of a flight. The PF does most of the flying, except in defined circumstances such as planning for descent, approach and landing. The PM carries out support duties and monitors the PF’s actions and the aircraft’s flight path.
- Flight level: at altitudes above 10,000 ft in Australia, an aircraft’s height above mean sea level is referred to as a flight level (FL). FL 170 equates to 17,000 ft.
- Eastern Standard Time (EST): Coordinated Universal Time (UTC) + 10 hours
- Feathering: the rotation of propeller blades to an edge-on angle to the airflow to minimise aircraft drag following an inflight engine failure or shutdown.
- MAYDAY: an internationally recognised radio call announcing a distress condition where an aircraft or its occupants are being threatened by serious and/or imminent danger and the flight crew require immediate assistance.