Pilatus PC-12 N978AF

The two airline transport pilots reported that takeoff acceleration in the single-engine, turboprop-equipped airplane was normal; however, shortly after rotation and during initial climb, a crew alerting system (CAS) warning activated. The CAS indicated excessively high engine torque. According to the copilot, who was the pilot flying, when he looked down, he saw a torque value of 5.3 pounds per square inch (psi). The pilot, who was monitoring from the left seat, reported that he saw a "low torque CAS message." He added that the copilot told him to "declare an emergency and run the checklist." With about 2,700 ft of runway remaining and the airplane at 200 ft mean sea level, the copilot chose to land immediately and executed a 90° left descending turn to land in grass. The airplane touched down and rolled about 600 ft before impacting a ditch, which resulted in substantial damage to the airplane and a postimpact fire. Data retrieved from the airplane's modular avionics unit revealed that all engine indications and parameters were normal throughout the takeoff roll and rotation; however, during the initial climb, the torque indication increased rapidly from about 45.0 to 71.0 psi; fault history data confirmed that the engine torque caution and warning were displayed during this time and that the other engine parameters remained normal. Four seconds later, the torque decreased to 47.3 psi, which coincided with a simultaneous drop in other engine parameters, consistent with the copilot reducing engine power following the CAS warning. The CAS was not equipped to display warnings for low torque values; a CAS warning or caution would only activate if an exceedance of torque tolerances occurred. Therefore, although both pilots reported seeing a low torque indication, given that the CAS is not equipped to display warnings for low values and that the data did not indicate a low torque condition occurred during the flight, it is likely that the pilots misinterpreted the CAS warning. Examination of the engine and torque indicating system revealed no evidence of any preaccident mechanical malfunctions or failures that would have precluded normal operation, and the cause of the high torque indication could not be determined. Given that no anomalies were found with the engine and torque indicating system during postaccident examination and that all other engine parameters remained normal throughout the flight, it is likely that the high torque indication was erroneous. The Pilot's Operating Handbook for the airplane stated that, following a CAS warning or caution for engine torque, engine power should be reduced if the torque value was above 44.3 psi. It also stated that, if the CAS warning or caution remained after the engine power was reduced, then the airplane should be landed as soon as possible using minimum power. Despite the pilots' misinterpretation of the torque indication, they should have followed the POH guidance on how to respond to an engine torque indication. However, the pilots chose to declare an emergency and immediately land after seeing the CAS warning during a critical phase of flight rather than troubleshooting the CAS message by reducing engine power to determine whether the CAS message could be resolved and despite onboard data indicating that the reduction in power resulted in the torque value returning to normal. The pilots reacted by reducing engine power substantially, which left them with no option but to conduct an off-runway emergency landing.

Quoted verbatim from the NTSB record.