Zitat

The aircraft was on an RNAV approach to Sydney's runway 16L with the first officer (ATPL, 3,250 hours total, 26 hours on type) being pilot flying and the captain (ATPL, 11,195 hours total, 6,666 hours on type) being pilot monitoring. The instrument landing system was not available at that time. The autopilot was engaged with the pitch channel in vertical speed mode rather than vertical navigation mode. The approach began in instrument meteorological conditions that gradually improved to visual meteorological conditions prior to landing.

When the aircraft flew past the instrument approach fix the crew felt time pressure to complete all necessary checklists and actions for the approach. At around that time the captain noticed the aircraft was no longer in icing conditions and selected the ice protection switch off however without communicating this to the first officer. While taking this action the captain however did not turn off the increased reference speed switch, that is normally selected on in icing conditions to reduce the angle of attack and thus increased the reference speed at which the stick shaker activates to provide an increased stall margin in icing conditions.

The aircraft was initially high on the approach but managed to get back onto profile however was above target speed requiring slow down. The captain therefore selected the propellers to maximum rpm which changed the pitch of the propellers and thus introduced a significant slow down of the aircraft, at the same time the power levers were retarded to idle. This configuration was kept until the aircraft reached the final approach fix (FAF), the aircraft at that point had not yet been configured for landing, gear was still up and the flaps were still retracted according to the first officer while the captain stated the gear was down and flaps still retracted before overflying the FAF.

Just before overflying the FAF the captain noticed the airspeed decelerated through 130 knots and called "airspeed". At about the same time the autopilot began to pitch the aircraft up to capture the preselected altitude, the airspeed thus dropped to 114 knots (computed regular stick shaker activation speed 99 knots), the stick shaker activated and the autopilot disconnected.

The captain called "stickshaker" and took control of the aircraft advancing the power levers before continuing the descent. The first officer assumed the role of pilot monitoring and worked the relevant checklists including extending flaps to 15 degrees. The aircraft was fully stabilized at 500 feet AGL and continued for a safe landing.

After landing the first officer spotted the increased reference speed switch was still in the position ON.

The ATSB reported the captain said in post flight interviews the use of vertical speed mode in the vertical channel of the autopilot was to increase the first officer's awareness of ground speed and vertical speed, the first officer had shown some deficiencies in these areas during simulator training, so that the aim was to improve the first officer's skill at maintaining a vertical profile without use of VNAV mode. The captain was aware that this would also increase his workload in monitoring the approach. They were surprised by the clearance for a RNAV approach as they had expected a different approach and now needed to rebrief the procedure.

The first officer was having issues with the captain and did not feel comfortable speaking up in the line training environment. For this reason the first officer had been scheduled to fly with another line training captain, which should have become effective in the next few days.

The first officer used non-standard phraseology during the approach due to feeling overloaded, the captain however did not recognize the first officer's overload situation. The non-standard phraseology as well as the overload situation however affected the approach.

The ATSB analysed that due to the increased reference speed switch still being turned on the stick shaker activated at about 10 knots higher a speed than configured. The slow down together with the pitch increase during altitude capture thus resulted in the stick shaker activation above configured reference speed.

The ATSB further analysed: "Following the stickshaker activation at around the final approach fix (FAF), the aircraft was not configured for landing and the speed was not stable. According to the operator’s SOPs, if the safe continuation of the flight is in doubt, a go-around is to be conducted. Given a stickshaker activation is an indicator of an impending stall, which could affect the safety of the flight, a lower risk option for the crew was to have conducted a go-around."

The ATSB continued the selection of VS mode in the autopilot's pitch channel was a deliberate decision by the captain which given the first officer's level of training and experience was not appropriate and unnecessarily increased the workload of both flight crew.