Colorado Aviation Accidents & Incidents

HISTORY OF FLIGHT

On July 7, 2014, a Piper Meridian PA-46-500T airplane, Registration Number N406CD, was holding short of the runway, ready for departure at Denver Centennial Airport, Colorado, when the engine, a Pratt & Whitney (P&WC) PT6A-42 failed to accelerate after two attempts of the pilots' power lever commands. After calling the tower and cancelling his takeoff clearance, the pilot planned to taxi away from the 'hold short line' and elected to use the fuel control unit (FCU) emergency manual over-ride (MOR) lever to increase the engine power. The sudden excess fuel in the combustor resulted in a turbine over-temperature. The pilot stated that as soon as he took the MOR lever out of detent, he heard a bang and saw a big ball of fire at the nose of the airplane and believing the airplane was on fire, he retarded all the levers, shutting the engine down and exited the airplane. He noted several small grass fires in the field which, later, were determined to have been ignited by hot fragments of the over-heated turbine blades that exited the exhaust pipe.

The pilot stated that he believed that his use of the MOR was in accordance with the Piper pilot's operating handbook (POH). He further stated that he did not believe that using the MOR lever was a cause of the engine over-temperature and failure since he did not even advance it, but that in retrospect, he would not have used it if he were to do it all over again.



INITIAL ENGINE EXAMINATION

The airplane was transferred to Tempus Aircraft, in Englewood, Colorado and on July 10, 2014 the engine, while it was still installed on the airplane, was examined for any possibilities of control system hardware failures or rigging errors. Distress and fracture of the engine's compressor and power turbines was confirmed and fragments of the power turbine were found in the exhaust plenum and ducts. The examination further revealed that all FCU control pressure (Py and P3) lines were intact, secured and leak-free. Further, the FCU control linkage and cabling from cockpit quadrant to the power lever (PL) and the MOR lever were connected and operated smoothly and with full range of travel. The MOR linkage was further examined for any rigging errors. The lever resided in the detent properly and a positive force was required to lift the knob over the gate and out of the detent to actuate. When out of the detent, the lever appeared to have no free-play and even required positive force to advance it.



REVIEW OF AIRFRAME GARMIN DATA

Data from the Garmin onboard readout device was downloaded and reviewed by the NTSB recorder laboratory. During the last taxi, the engine was observed to be in a decaying sub-idle condition with gas generator speed (Ng) approximately 39% (normal idle Ng is 64%) and inter-turbine temperature (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 o