Piper PA46 500TP N406CD

AIRFRAME ENGINE CONTROLS Before the engine was removed, an examination of the aircraft after the event revealed that all FCU control pressure (Py and P3) lines were intact, secured and leak-free. Additionally, the FCU control linkage and cabling from cockpit quadrant to the power lever (PLA) and the MOR lever were connected and operated smoothly and with full range of travel. The MOR linkage was further examined and no rigging errors were detected. Findings: No engine control rigging errors on the airframe were detected. ENGINE On September 16-18, 2014, the engine was examined at the P&WC facility in Montreal, Canada. Findings: Examination of the engine and accessory components revealed no anomalies that would have contributed to the reported event. GARMIN DATA A review of the data from the Garmin onboard readout device revealed that during the last taxi, the engine was allowed to decay to a sub-idle condition with gas generator speed (Ng) approximately 39% (normal idle Ng is 64%) and ITT 830° Celsius (°C) when Ng increased to approximately 47% and the ITT almost to 1300° C, corresponding to the activation of the MOR. According to the P&WC manuals, the maximum operating turbine temperature limit for takeoff is 800°C while the maximum allowable transient (limited to only 5 seconds) temperature during starting is 1000 °C. Turbine engines, at idle, require a minimum speed to operate. When operating below this speed, the compressor is operating in an inefficient manner, and cannot supply enough cooling air to the core components, causing a hot condition. When, in this already hot condition, an acceleration demand is made of the engine, excess fuel is injected into the combustor, further heating the core components, causing an overtemperature. High bleed air demands from the engine at idle can cause a decaying rpm condition. During this event, a hot day caused the pilot to increase air conditioning in the cabin which took considerable bleed air from the engine, which may have caused a decrease in RPM. To correct this decrease, the pilot must simply increase the power lever until idle speed is maintained. If the pilot does not pay attention to the idle RPM, and allows it to go to a sub-idle condition, a 'bog-down' may result and the fuel control will sense this and refuse to accelerate. The only option for the pilot is to shut the engine down and re-start. If the MOR is used at this time, an engine overtemperature and failure will likely result. Findings: The pilot did not pay attention to the engine indications and allowed the engine to 'bog down'. His subsequent use of the MOR caused the overtemperature and failure of the engine. Based on the pilots' statement, the Garmin readout data, and the lack of any anomalies in any of the engine accessories, it was concluded that the cause of the fire from the exhaust was due to the sudden introduction of fuel by the activation of the MOR, which along with the sub-idle speed condition of the engine at the time of the activation, resulted in a significant high temperature exposure of the CT blades, and their subsequent distress and failure of the engine. PIPER MERIDIAN POH MOR GUIDANCE The pilot stated that he believed that his use of the MOR was in accordance with the Piper pilot's operating handbook (POH). A review of the Piper POH Section 4 - Normal Procedures (Reference: Piper Report: VB-1689 – Revision June 4, 2013) revealed that the Piper guidance was contrary to the P&WC recommendations, which states "the emergency manual override system which is intended to be used in the event of a loss of Power Lever (PLA) control due to loss of air pressure to the Fuel Control Unit (FCU) during flight.", Piper guidance allows pilots to use the MOR on the ground, even at sub-idle RPM conditions, and further, gives the impression that reverting to the MOR is a normal procedure rather than an emergency procedure. Findings: A review of the Piper POH revealed an error in the guidance for MOR operation.

Quoted verbatim from the NTSB record.