REX SF34 at Perth on Jul 6th 2021, stick shaker activation
Last Update: March 9, 2022 / 19:55:02 GMT/Zulu time
On Mar 9th 2022 the ATSB released their final report concluding the probable causes of the serious incident were:
- The aircraft’s right wing inboard de-ice boot probably delaminated shortly before encountering icing conditions, triggering the de-ice system fault that led to the flight crew’s decision to return to Perth.
- The pilot flying became task saturated due to high workload and did not notice the reducing airspeed, which was also missed by the pilot monitoring due to a focus on other tasks until the stick shaker activated.
The ATSB analysed:
Shortly after the aircraft departed Perth, the flight crew received cockpit indications of a de-ice system fault. The fault was probably triggered by a delaminated de-ice boot on the underside of the right wing that failed during its inflation cycle shortly before encountering icing conditions. With a low freezing level and forecast icing conditions along the planned route, the de-ice fault indication led to the flight crew’s decision to return to Perth.
While manoeuvring towards Perth, engine power was reduced to descend the aircraft from 7,000 ft to 5,000 ft. However, when the aircraft levelled off at 5,000 ft, engine power was not increased. Consequently, as the airspeed reduced due to the low engine power, the autopilot maintained the selected altitude (5,000 ft) by pitching the nose up, increasing the AOA and reducing the airspeed further. This condition went unnoticed until one of the AOA sensors reached the level required for stick shaker activation.
The first officer, the pilot flying in the time leading up to the stick shaker activation, probably became task saturated while managing flying tasks (changing flight state to descend, level flight and turn) as well as communicating with, and following ATC instructions. This task saturation reduced the attention that the first officer paid to managing the airspeed and engine power. At that time, the captain (pilot monitoring) was also not monitoring these key parameters due to a focus on other communication tasks related to the return to Perth. The crew’s reduced awareness of airspeed resulted in the potential stall going unnoticed until the stick shaker activated.
In addition, during that rapid sequence of events, neither pilot recognised the first officer’s high workload and task saturation. Consequently, no attempt was made to alleviate the situation, for example by discontinuing the approach or deferring ATC requests for information until the aircraft was straight and level. Such actions would have provided additional time and opportunity for the crew to refocus on flight instruments and key parameters.
Aircraft Registration Data
This article is published under license from Avherald.com. © of text by Avherald.com.
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