CEN16FA315

The improper execution of an autorotation following the loss of engine power, which resulted in an uncontrolled descent into terrain. Contributing to the accident was the flight instructor's lack of remedial action during the autorotation.

The flight instructor and student pilot were flying the helicopter near dusk about 1,100 ft above ground level (agl) when the instructor initiated a practice autorotation, by reducing the throttle to idle. The engine subsequently experienced a total loss of power; the instructor attempted to restart the engine, but, was unsuccessful. The student provided conflicting statements regarding who was controlling the helicopter during the autorotation and landing, but stated that he started the landing flare about 25 ft agl. He further stated that he did not think that the helicopter's descent had been sufficiently slowed before the helicopter impacted the ground. Upon impact, the tail boom partially separated and the helicopter rolled over, coming to rest on its right side. Postaccident examination of the helicopter and engine did not reveal any mechanical malfunctions or anomalies that would have precluded normal operation. Impact damage precluded any functional testing of the engine and its components, and the reason for the reported loss of engine power could not be determined. The pilot's flight manual stated that an engine restart should not be attempted below 2,000 ft agl, and that, below that altitude, the pilot should conduct a normal autorotation to landing. The manual also stated that the fuel boost pump should be activated before a practice autorotation. The fuel boost pump switch was found in the OFF position. The manual also states that rapid throttle reductions to full idle during flight shall not be conducted at any altitude to minimize the possibility of engine stoppage.

The Pilot's Flight Manual found at the accident site was last updated in June 2000. According to the manufacturer, there had been nine revisions since that date, with the latest revision November 19, 2014. A complete re-issue was published December 7, 2012, which included new warnings on practice autorotations and throttle management. According to the Pilot's Flight Manual (revised July 5, 1996) that was located at the accident site, Emergency Procedures, page 3-1, Section 3-1 Engine Failure – Altitude Above 450 Feet, stated in part: "Lower collective pitch. Enter normal autorotation. Establish a steady glide of 52 knots (60 mph) IAS approximately. At an altitude of 50 feet, begin steadily to apply back cyclic stick to decreased forward airspeed. At approximately 10 feet, coordinate collective pitch with forward movement of cyclic stick to level ship and cushion landing. Make ground contact with ship level." The Pilot's Flight Manual (revised July 5, 1996) Emergency Procedures, page 3-7, Section 3-11 Air Restart stated in part: "Pick out landing spot. If less than 2000 feet above terrain, proceed with autorotation landing. Pull mixture control to IDLE CUTOFF when time permits to stop flow of fuel from nozzles." The Pilot's Flight Manual (revised June 15, 1994) Normal Procedures pages, 4-20 to 4-22, Pilot's Check of Idle Mixture, Idle Speed, and Fuel Boost Pump, stated in part: "NOTE: This check of idle mixture, idle speed, and fuel boost pump shall be accomplished at the end of the last flight each day, prior to engine shutdown. Accomplish the engine idle mixture check as follows: Land from a hover with engine cylinder head temperature and oil temperature as near to in-flight conditions as possible, friction on the collective and cyclic controls, governor disengaged, and engine speed at operational rpm. Ensure MIXTURE is set to FULL RICH. Rapidly rotate throttle to CLOSED position. (Set at normal idle stop, do not override.) NOTE: Engine speed with immediately decrease to idle level. Rotor speed, however, will decline gradually. The next step must be performed before rotor tachometer needle superimposes with engine tachometer needle. Observe engine tachometer need and smoothly move mixture control toward IDLE CUTOFF position. Return mixture control to FULL RICH before the rpm decreases to a point where the engine will stop. NOTE: Engine rpm rise is required to be between 25 and 100 rpm for this check. If rpm rise is not within the required limits, notify the appropriate maintenance personnel to perform proper idle speed and mixture adjustments. Accomplish an idle speed check as follows: Operate helicopter at operational rpm with rotor system engaged, friction on the collective and cyclic controls, and governor disengaged. Rapidly rotate throttle closed and into full override position. Read and record engine idle rpm to engine and rotor tachometer needles superimposing. With engine head temperature near 300 degrees F, but not above, repeat the three preceding steps, without going into full override (set throttle at normal idle stop). NOTE: The first check (throttle into full override) should produce an idle speed no less than 1400 rpm. The second check (throttle at normal idle stop) should produce an idle speed no greater than 1600 rpm. If engine idle speed is not within the required limits, notify the appropriate maintenance personnel to perform adjustments in accordance with the Basic HMI." The November 2014 revision of the Pilot's Flight Manual Normal and Emergency Procedures sections included the following warnings and instructions: "Engine idle speeds at high density altitude may be less than those set at sea level conditions. Do not rapidly reduce throttle to idle stop in flight. WARNING – To minimize possibility of engine stoppage, rapid throttle reductions to full idle during flight shall not be conducted at any altitude." "WARNING – During power recovery from practice autorotations, airspeed and altitude combinations that are inside the height velocity curve shall be avoided. High rates of descent may develop from which recovery may be difficult or not possible. WARNING – Practice autorotations shall be conducted in an area with a suitable landing site available to minimize hazards associated with inadvertent engine stoppage. WARNING – To reduce the chance of engine stoppage when initiating practice autorotations or simulated forced landing training the throttle shall not be abruptly retarded to the idle position. CAUTION – At high power settings an overspeed might occur if throttle is not reduced slightly when collective is lowered. Ensure fuel boost pump is activated prior to commencing autorotation training. Split the needles by reducing throttle slightly and lowering the collective. The throttle correlation will establish a high idle rpm (approximately 2500 rpm) which will aid in preventing the engine from loading up or stalling during recovery. Conversely, for recovery, increase throttle slightly when the collective is raised, the correlation is such that only minor throttle adjustments will be required to perform a smooth recovery without exceeding 3200 rpm. If engine stops make a touchdown auto landing." Review of sun and moon data from the U.S. Naval Observatory revealed that, on the day of the accident, sunrise was at 0644, sunset was 2018, and the end of civil twilight was 2045. The instructor died in the hospital on August 10, 2016. The Dallas County Office of the Medical Examiner, Dallas, Texas, performed an autopsy on the instructor. The autopsy report stated that the cause of death was blunt force injuries. The FAA's Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed forensic toxicology on specimens from the flight instructor. The results were negative for carbon monoxide and ethanol. Testing identified Acetaminophen (31.2 (ug/ml) in the urine, glucose (160 mg/dl) in vitreous, glucose (18 mg/dl) in urine, and the blood sample was unsuitable for analysis of Hemoglobin A1C. Acetaminophen is a pain and fever reliever commonly sold under the trade name Tylenol. According to the FAA inspector who spoke with the student, the student had accumulated 25 flight hours with a local helicopter flight school before flying with the accident instructor. He'd stopped flying with the local flight school in October 2012. Since October 2015, the student had flown several flights with the instructor and had accumulated 63.7 total flight hours at the time of the accident. According to law enforcement, on July 12, 2014, the student had been involved in a previous accident in the same make/model helicopter. The student stated to the FAA inspector that he was moving the helicopter when the helicopter "got away from him." The accident was not reported to the NTSB. The helicopter's most recent annual inspection (which included an annual, 100, 200, 400 and 24-month inspections) was completed on August 10, 2015, at a total airframe time of 5,624 hours and a Hobbs meter time of 13.0 hours. At the time of the inspection, the engine had accumulated 3,664.6 total hours and 392.6 hours since overhaul. The Hobbs meter time at the accident site was 52.7 hours. Review of maintenance records revealed no entries or comments related to idle/mixture adjustments or settings. The helicopter impacted down sloping grassy terrain adjacent to wooded areas and residential structures. The main wreckage consisted of the fuselage, a portion of the tail boom, and the main rotor system. The landing gear skids were spread apart and bent up into the fuselage. The