What happened
On 8 June 2023, a Regional Express Saab 340, registration VH-TRX, was conducting an air transport flight from Sydney to Merimbula with 22 passengers and 3 crewmembers. During the descent, the crew activated the engine and wing anti-ice systems due to expected icing conditions. This action also engaged the aircraft's ice speed system, which modifies the stall warning activation angle of attack.
While performing a visual approach to runway 21 in turbulent conditions, the captain reduced engine power to flight idle to prevent exceeding the maximum flap speed. Because the autopilot was engaged in vertical speed mode, this reduction in thrust caused the aircraft to continue decelerating. During this period, the crew also attended to setting the windscreen wipers due to a rain shower. The airspeed eventually dropped to 109 kt, triggering the stall warning. The captain immediately responded by increasing power and adjusting the pitch, allowing the aircraft to recover and land safely without damage or injuries.
The investigation
The investigation examined the flight data, weather records, and crew actions. Investigators noted that while the aircraft was no longer in icing conditions, the ice speed system remained active according to operating procedures. This system had lowered the threshold for the stick shaker and aural alerts. The investigation also reviewed meteorological data from Merimbula Airport, which showed a gust front passing through the area during the approach, contributing to the turbulence encountered by the crew.