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The crew of a SAAB SF340B reported that shortly after takeoff from Sydney Airport, NSW, they observed a zero reading on the left torque gauge and advised air traffic control that they were returning to land. During the approach, the crew made a PAN broadcast and advised that the left engine had been shut down. After landing the crew reported that they experienced airframe vibration and suspected a tyre had blown on landing. An inspection by emergency services personnel did not find any damage to the tyres and the crew taxied the aircraft to the terminal apron.

An examination of the aircraft systems could not find any reason for the zero reading on the left torque gauge, but the left digital engine control unit was replaced. A review of the crew's actions after they observed the loss of torque indication on the left torque gauge, found that they had selected the 'autocoarsen' switch to ON, prior to landing. That was contrary to directions in the flight crew operations manual that required the switch to be selected OFF when torque gauge indications read zero or were erratic. Consequently, the left propeller blades were automatically coarsened, effectively feathering the left propeller and resulted in an asymmetric landing.

The operator issued a notice to its aircrew reminding them of the requirement in the flight crew operations manual to not select 'autocoarsen' in these circumstances.

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