N536EMSocata TBM 700 · 2010

On October 5, 2014, about 1255 eastern daylight time, a Socata TBM 700 (850), N536EM, was force landed onto a high school sports field near Fayetteville, Georgia. The commercial pilot received minor injuries and one passenger, his wife, had serious injuries. The airplane was registered to TBM 850 536 LLC and was operated by pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Day, visual meteorological conditions prevailed for the flight, and an instrument flight rules flight plan was filed. The flight originated from Dekalb-Peachtree Airport (PDK), Atlanta, Georgia about 1240 and was destined for Pine Mountain, Georgia (PIM).

The pilot reported the following. During cruise flight at 6,000 feet above mean sea level (msl), he observed an oil pressure message on the crew alerting system (CAS) and a total loss of engine power. The air traffic controller provided vectors to Falcon Field, Peachtree City, Georgia (FFC), and later the pilot reported that he would not make the runway. An engine restart was not attempted. He feathered the propeller, placed the power lever in idle, and the condition lever to cut off. The landing gear and flaps remained in the retracted positions. Radar contact was subsequently lost and the pilot force landed the airplane. The airplane collided with trees and the ground before coming to rest upright. There was no fire. The pilot and his wife exited the airplane and were transported to a local hospital for treatment.

The pilot, age 66, held a commercial pilot certificate with ratings for airplane single engine land and instrument airplane. He reported a total flight experience of 4,244 hours, including 411 hours in the accident airplane make and model. He possessed a class 3 Federal Aviation Administration (FAA) medical certificate with no limitations.

The pilot completed a TBM 850 recurrent training course at SIMCOM, Orlando, Florida on January 24, 2014.

The accident airplane was a Socata model TBM 700 (850), serial number 536, manufactured in 2010. It was a single engine low-wing monoplane of mainly aluminum construction. It had a retractable tricycle landing gear and was configured to seat six occupants. The airplane was powered by a Pratt & Whitney Canada PT6A-66D engine, serial number RV0159, rated to produce 850 shaft-horsepower. It was fitted with a Hartzell HC-E4N-3, four-bladed, constant speed propeller.

An examination of available maintenance records revealed that an annual inspection was completed on the airframe and engine on January 8, 2014. The airframe total time at the time of the accident was 719.8 hours. The time since the last annual inspection was 135.6 hours.

The 1253 surface weather observation for FFC, located about 3 nautical miles west-northwest of the accident site, included sky clear, wind calm, visibility 10 statute miles or greater, temperature 64 degrees F, dew point 36 degrees F, and altimeter setting 30.06 inches of mercury.

The accident airplane was a Socata model TBM 700 (850), serial number 536, manufactured in 2010. It was a single engine low-wing monoplane of mainly aluminum construction. It had a retractable tricycle landing gear and was configured to seat six occupants. The airplane was powered by a Pratt & Whitney Canada PT6A-66D engine, serial number RV0159, rated to produce 850 shaft-horsepower. It was fitted with a Hartzell HC-E4N-3, four-bladed, constant speed propeller.

An examination of available maintenance records revealed that an annual inspection was completed on the airframe and engine on January 8, 2014. The airframe total time at the time of the accident was 719.8 hours. The time since the last annual inspection was 135.6 hours.

An inspector with the Federal Aviation Administration (FAA) responded to the accident site and examined the wreckage. The wreckage came to rest, upright, on level ground at a high school sports complex. The fuselage and both wings exhibited structural damage and both wing fuel tanks were ruptured from impact forces. The landing gear and wing flaps were found in the retracted positions. There was evidence of fuel spillage throughout the wreckage path. The propeller and gearbox were broken free from the engine. The engine remained attached to the firewall.

All major airframe structural and flight control components were accounted for within the wreckage debris field. Flight control continuity was established from the cockpit controls to the ailerons, elevator, and rudder. The fuel tank selector handle was found in the "L" (left) tank position.

Fuel Tank Design

The airplane had integral fuel tanks formed by sealing of the structure in each wing. Each tank was divided into an inboard (feeder) area and an outboard (storage) area. The feeder section of each fuel tank was formed by the root rib and the second rib outboard from the root. This rib contained one-way valves that would allow fuel to flow from the outboard storage area into the inboard feeder area, but prevented fuel from flowing outboard. The fuel capacity of the feeder section of the tank was about 33 liters or about 8.7 gallons. The one way valves in the feeder section were intended to prevent unporting of the fuel tank pickup due to momentary periods of uncoordinated flight as would be encountered during turbulence, but were not intended to do so for extended periods of uncoordinated flight.

Autopilot and Yaw Damper Systems

The airplane was equipped with an automatic flight control system (AFCS) that included an autopilot and yaw damper. The autopilot controlled the aircraft pitch and roll attitudes following commands received from the flight director. The yaw damper system operated independent of autopilot and was designed to monitor lateral acceleration to achieve coordinated flight. The system was also designed to automatically actuate the rudder trim to achieve trimmed flight. The automatic trim feature was only enabled when the yaw damper system was engaged. The rudder trim system also included a manual electric yaw trim (MEYT) switch on the pilot yoke that enabled the pilot to trim the rudder without yaw damper engagement. The yaw damper system could be enabled independent of the autopilot by depressing the "YD" button. In addition, if the pilot selected the "AP" key, the autopilot, yaw damper and flight director would be activated simultaneously. The yaw damper system could be disengaged by activating the MEYT switch located on the yoke, or by depressing the "YD" button. The parameters recorded by the G1000 avionics system did not include a discrete parameter indicating yaw damper engagement or trim motor actuation.

The G1000 indications of extended flight in a slip condition were indicative of the yaw damper being disconnected while the autopilot was engaged. Steady heading side slips occur with no trim action on the yaw axis as the aircraft increases speed and maintains a steady heading and altitude. Rudder trim was provided automatically with the yaw damper on, or manually using the rudder trim. During a post-accident interview with the pilot, he stated that he was not aware of a side-slip condition prior to the loss of engine power.

On September 8, 2014, TBM issued Service Information (SI) 2014-006, which provided an upgrade (version 14.02) to the G1000 version 14.01 software. Included in the upgrade was a new CAS caution message, "AP ON YD OFF" that illuminated when the autopilot was on while the yaw damper was off. This condition would include a scenario of inadvertent pilot deactivation of the yaw damper. An aural warning was also incorporated to direct the pilot to the CAS message. At the time of the accident, the accident airplane did not have the upgrade to version 14.02 installed. The owner reported that he planned to install it at the next annual inspection, due in January, 2015.

Chapter 3 of the TBM 850 Pilot's Operating Handbook addresses engine failure in flight. Step number 8 of the ENGINE FAILURE DURING FLIGHT checklist calls for an air start attempt and directs the pilot to the air start procedure (section 3.4). The pilot reported that he did not attempt an air start.

The airplane was equipped with a Garmin G1000 all-glass avionics suite. The unit held a Secure Digital (SD) card and investigators confirmed that the card recorded flight and systems data before and during the accident sequence.

GPS track data, retrieved from the Garmin G1000 system, depicted the airplane departing PDK about 1240. About 18 seconds after takeoff, the autopilot was turned on. G1000 data indicated that during the climb portion of the flight, the lateral acceleration values were near neutral. This indicated that the rudder trim was appropriately set for the climb portion of the flight.

About 1244:52, the airplane reached 6,000 feet above mean sea level, leveled off, and began to accelerate. During the next 5 minutes, the airplane's lateral acceleration reached 0.17g while the airplane maintained a left bank of about 8-10 degrees while on a heading of about 190 degrees. These roll, lateral acceleration, and heading values indicated that the airplane was flying in a side-slip.

At 1249:53, the airplane started a right turn with the autopilot engaged, to a heading of 240 degrees. At the end of the turn, at 1250:16, the engine lost power. A sudden drop of NG (gas producer speed), torque, and fuel flow was observed. At 1251, the pilot disconnected the autopilot and the airplane returned to near-coordinated flight until the airplane completed its descent to the forced landing.

Fuel System

The aircraft fuel system was examined after recovery of the wreckage to a storage facility. The cockpit fuel selector was in the LEFT tank position and the fuel selector valve indicated that fuel was feeding from the left tank. Both inboard wing fuel doors were opened to inspect the pickup area; no anomalies were found. The fuel screen, low fuel sensor, and flapper valves all appeared normal.

The fuel lines from the left tank to the engine were examined for obstructions with forced air; none were found. The fuel filter was removed and examined; no contamination was found. The fuel selector valve operated in a normal manner.

Engine

The engine was removed and sent to the manufacturer's facility for disassembly and examination. The engine displayed moderate impact damage including structural separation of the forward reduction gearbox, impact fracture of the propeller shaft, and light compressional deformation of the exhaust duct.

The gas generator rotor and accessory gearbox turned freely by hand. Light circumferential rubbing was displayed by the compressor turbine shroud due to contact with the adjacent blade tips. Unburned organic debris was distributed in the combustion section. The power section was seized due to the deformation of the exhaust duct. Circumferential rubbing was displayed by the first and second stage power turbine shrouds due to contact with their adjacent blade tips. None of the engine mechanical components displayed any indications of any pre-impact anomalies or distress.

Investigation of the engine controls and accessories included functional testing of the fuel pump, fuel control unit, flow divider, fuel nozzles, and torque limiter. The propeller governor was disassembled and inspected as impact damage precluded functional testing. None of the components showed any conditions that would have precluded normal operation.

Rudder Trim System

The electrical rudder trim actuator was found positioned slightly left of neutral. Electrical power was applied to the rudder trim and yaw damper systems after the accident and both operated in a normal manner.