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On August 13, 2009, at 1230 Pacific daylight time, a Eurocopter AS 350 B2, N217LA, landed hard following a practice 180-degree autorotation at William J. Fox Field (WJF), Lancaster, California. The Los Angeles Police Department (LAPD) – Air Support Division (ASD), operated the helicopter under the provisions of 14 Code of Federal Regulations Part 91, as a public-use proficiency flight. A certified flight instructor (CFI)/check pilot and two certificated commercial pilots were all seriously injured. The helicopter was substantially damaged. The flight departed Van Nuys Airport (VNY), Van Nuys, California, at 1130. No flight plan had been filed.
All three pilots stated that prior to departure from VNY, the weather in the area was reviewed and WJF was chosen due to the clear conditions. Training is normally done at the airports in Los Alamitos and Point Mugu, California. En route to WJF they obtained ATIS information, which indicated visibility more than 6 statute miles, clear skies, wind at 12 knots gusting to 19 knots. They also discussed the “4H’s – High, Hot, Heavy, and Humid, and how they affected flight.” Upon arrival at WJF, the altimeter was set to the field elevation, and the intent was to initiate all maneuvers at 500 feet above ground level. All three pilots reported that several maneuvers were performed with no issues identified. The flight continued with two 180-degree autorotations. The CFI reported that while performing the first 180-degree autorotation, the helicopter was not going to make the intended landing spot, it was steeper than normal; he advised the flying pilot that he was going to reapply power to execute a go-around. On the second 180-degree autorotation, the accident, the pilots stated that the maneuver was initiated at 500 feet agl. According to the CFI, while on downwind he cut the power and the flying pilot turned the helicopter onto the first 90 degrees with no issues. The helicopter developed a high sink rate and was pushed away from its intended landing spot. The CFI reapplied power, and stated that the engine did not come back online. The flying pilot remained on the controls and returned the helicopter to a straight and level attitude before it struck the dirt.
According to the LAPD instructor’s guide to helicopter flight maneuvers, under the section Autorotations Instructional Techniques, a power recovery is used to terminate practice autorotations. Following a power recovery, a landing can be made or a go-around initiated. Under the section titled Non-Standard Autorotations, an autorotation with a turn (180-degree autorotation) requires an entry altitude of 700 feet agl or higher for practice.
Normal training locations are Los Alamitos Army Airfield (SLI), Los Alamitos, and Point Mugu Naval Air Station (Naval Base Ventura County; NTD), Point Mugu. Both airports have dedicated Aircraft Rescue and Fire Fighting (ARFF) crews and equipment. William J. Fox Field Airport does not have dedicated ARFF crews and equipment.
According to LAPD personnel, patrol altitude can be between 500-800 feet.
The helicopter’s aircraft flight manual (AFM) includes a training procedure for autorotations. This procedure allows for full autorotation with a simulated engine flame-out or loss as opposed to a power recovery. The AFM training procedure is as follows:
-Lower collective to enter autorotation.
-Maintain NR within the green range of the NR indicator.
-Reduce power maintaining the Ng above 67%.
-Apply autorotation procedure SECTION 3.1. paragraph 2.1, page 1 of the present Flight Manual except for the engine, fuel shut-off cock and electrical items.
-After landing, with the collective at full low pitch, bring the fuel flow control lever to the “flight detent”.
-Rotor speed accelerates to its normal governed value.
The procedure further notes that autorotation training shall be conducted within gliding distance to a landing site suitable for a running landing. Furthermore, it should be noted that the steps to lower the collective and maintain NR within the green range precede the step to reduce power.
Right-seat pilot (flying pilot)
A review of Federal Aviation Administration (FAA) airman records revealed that the 54-year-old pilot held a commercial pilot certificate with a rotorcraft-helicopter rating, as well as private pilot privileges for airplane single-engine land. The pilot held a second-class medical certificate issued on July 17, 2009. It had the limitations that the pilot must wear glasses for distant vision, and possess lenses for near vision.
In the National Transportation Safety Board Pilot/Operator Aircraft Accident/Incident Report (NTSB Form 6120.1), the pilot listed his total time as 9,200 hours with 5,700 hours in the accident make and model. He logged 90 hours in the last 90 days, and 30 in the last 30 days.
Left-seat pilot (CFI and non-flying pilot)
A review of FAA airman records revealed that the 50-year-old pilot held a commercial pilot certificate with ratings for airplane single and multi-engine land, rotorcraft-helicopter, and instrument airplane and helicopter. The pilot held a second-class medical certificate issued on February 25, 2009; it had no limitations.
In the National Transportation Safety Board Pilot/Operator Aircraft Accident/Incident Report (NTSB Form 6120.1), the pilot listed his total time as 2,764 hours with 1,073 hours in the accident make and model. He logged 112 hours in the last 90 days, and 27 in the last 30 days.
A review of the helicopter logbooks revealed that a 100/200-hour inspection had been completed and the helicopter was returned to service on July 30, 2009. Total time on the helicopter was 11,198.2 hours at the time of the inspection. On August 1, 2009, a 100/200-hour Starflex inspection was completed, followed by an operational check. The helicopter was then flown 8 days, which included the day of the accident for approximately 52 hours. A review of the records indicated that daily checks were performed with no major issues identified. An annual inspection was completed on June 2, 2009, at which time the helicopter had accrued 10,995.8 total flight hours.
According to an entry in the engine logbook, a Turbomeca, Arriel 1D1 serial number (S/N) 19030, engine had originally been installed on N661PD, another LAPD helicopter. On July 12, 2006, the engine was removed and installed on the accident helicopter, N217LA, along with a new fuel control unit, part number (P/N) 0164548720.
A review of the engine maintenance records revealed that in the preceding 90 days the engine had undergone a 100/200-hour inspection (July 30, 2009). The engine total time was recorded as 4,317.1 hours.
The airport, WJF, issued a special weather observation report at 1237, which indicated the wind was from 240 degrees at 13 knots gusting to 18 knots; visibility 25 statute miles; a scattered cloud condition at 7,000 feet; temperature 35 degrees Celsius; dew point minus 1 degree Celsius; altimeter setting 29.97 inches of mercury. The calculated density altitude was 5,214 feet.
According to the Airport/Facility Directory for WJF, the airport elevation is 2,351 feet.
WRECKAGE AND IMPACT INFORMATION
The accident site was at the south end of the airport. The helicopter came to rest upright on a magnetic heading of 250 degrees in a dirt area adjacent to taxiway A. The area was comprised of hard-packed desert terrain with relatively little vegetation near the helicopter. The first identified point of impact was approximately 35 feet to the left and behind the helicopter. The left skid had detached at the forward and aft cross tubes, and was located in the debris field. The right skid also separated from the cross tube supports, but remained underneath the helicopter. Fuselage skin and Plexiglas were also identified in the debris path.
The main rotor blades remained attached to the main rotor assembly atop the helicopter in its normal position. As denoted by the manufacturer, the main rotor blades are color identified as the red, yellow, and blue blades. The red blade exhibited trailing edge separation, as well as chordwise scratching 3 inches inboard from the tip on the underside of the blade. The yellow and blue blades exhibited some downward coning damage. The yellow blade exhibited trailing edge separation with some scratch marks on the underside of the blade. The blue blade had no trailing edge separation and minor scratch marks on the underside of the blade.
The tail rotor assembly remained attached to the tail rotor driveshaft. Both tail rotor blades remained connected via their respective hardware. The tail rotor blades exhibited leading and trailing edge damage, delamination, and torsional twisting. The tip of one of the tail rotor blades was broken and mostly separated from the remaining blade.
TESTS AND RESEARCH
On August 27-28, 2009, the NTSB, LAPD, American Eurocopter, and Turbomeca USA, convened at the Los Angeles General Services facilities at the Van Nuys Airport to perform an airframe and engine examination. Detailed inspection notes for the airframe and engine are in the public docket.
The visual examination revealed that the cabin area had sustained impact damage consistent with a high vertical rate of descent. Both the front pilot and copilot bucket seats were laterally fractured below the seat pan. The left rear seat, where the passenger was seated was deformed in a downward direction. The headliner had also dropped from the ceiling. The majority of the Plexiglas windows had fragmented and separated from their respective frames. The helicopter was equipped with dual flight controls. Both collectives were in between the mid- and high pitch position. Both cyclic sticks were forward and slightly to the right, and the anti-torque pedals were near the neutral position. Flight control continuity was established. The fuel flow control lever was in the OFF position and the fuel cutoff lever was in the aft cutoff position. Continuity was confirmed between the fuel flow control lever and the engine fuel control.
Investigators manually rotated the transmission with no binding noted. They also observed corresponding rotation of the Starflex main rotor head and transmission input flange. The yellow arm of the Starflex had a 45-degree angle fracture mark opposite the direction of rotation, consistent with a powered main rotor blade impact. The other two arms, blue, and red, were intact. The Starflex hardware, all main rotor controls, pitch links, swashplate, hydraulic servos, remained attached and appeared to be properly installed. Investigators observed impact marks between the main rotor blade bolts and the hub, consistent with excessive blade flapping. Examination of the main rotor blades revealed impact damage and rotational scoring near the tips. The manufacturer’s representative attributed the damage to ground impact. The trailing edges of the main rotor blades exhibited splitting consistent with a lower than nominal rotor rpm upon impact.
The fuselage to tail boom junction exhibited compression signatures on the lower side. The left horizontal stabilizer had an impact mark near the tip; according to the manufacturer’s representative, the direction of the scrape mark and dimension of the scrape were consistent with a main rotor blade strike. The right lower vertical fin and tail cone also exhibited compression signatures along with torsional damage. The landing gear skids separated at the ankles, and the cross tubes rolled aft. This condition allowed the belly of the fuselage to contact the ground.
The tail rotor exhibited impact damage consistent with ground impact. Investigators noted that both of the tail rotor strike tabs were bent inward. The tail rotor drive shaft showed rotational scoring forward to the aft tail rotor drive shaft spline coupling, and the spine coupling itself showed rotational scoring. The tail rotor drive shaft hanger bearings rotated freely.
The fuel tank and system were compromised during the accident sequence. The fuel filter was inspected with no debris observed. Investigators examined the caution warning panel; no filament stretch was observed on any of the bulbs. According to the manufacturer, the vertical acceleration was approximately 12 g’s.
Investigators visually examined the engine. The engine remained attached to the airframe at both the front and rear engine mounts. No fluids were observed leaking from the engine; oil was visible through the site glass, and the level appeared to be within limits. All of the hoses, pipes, and harnesses appeared to be intact and secured to the engine. The engine is comprised of five modules: Module 1 (MO1) – Transmission Shaft and Accessory Gearbox, Module 2 (MO2) – Axial Compressor, Module 3 (MO3) – Gas Generator High-Pressure Section, Module 4 (MO4) – Free Turbine, and Module 5 (MO5) – Reduction Gearbox.
Investigators noted no anomalies with MO1. The chip detectors and the magnetic plug were clear of debris. The starter/generator was removed and the splines examined with no deformation noted. The fuel filter bypass indicator had not popped, and when the fuel control lever in the cockpit was moved through its range, the fuel control lever on the fuel control unit moved accordingly.
Investigators were able to manually rotate the axial rotor with no unusual noises heard or roughness felt throughout the assembly. The axial blades were examined with no rub present. The bleed valve was in the open position and the nozzle guide vanes were not damaged.
Investigators noted no damage to the gas generator turbine casing. A borescopic inspection of the first stage turbine blades showed no damage.
Investigators reported that the containment ring was not damaged and the free turbine wheel assembly moved freely with no binding felt or grinding heard. The blades were undamaged and no blade tip rub was observed. The exhaust pipe was unremarkable.
Investigators stated that the reduction gearbox casing was unremarkable and the magnetic plug was free of debris.
On October 27-29, 2009, the NTSB, LAPD, American Eurocopter, and Turbomeca USA, convened at Turbomeca USA’s facilities in Grand Prairie, Texas, to further examine the engine. The shipping container was unpacked and personnel from Turbomeca USA inventoried the engine. A visual inspection of the engine revealed a dent on the linking tube. When the axial wheel was manually rotated the investigative team heard a grinding noise. The front stage turbine wheel was also manually rotated with no unusual noises heard. A borescopic inspection of the front swirl plate and front stage turbine wheel revealed no anomalies. The investigative team determined that an engine run in a test cell could be performed. A new fuel control unit fuel filter and a factory calibrated ECET torque transmitter were installed on the engine to facilitate the engine run. The engine was run in the test cell for 1 hour 22 minutes; with the exception of the bleed valve, which opened slightly above the opening threshold limit, the engine operated within specifications.
The helicopter was equipped with an AeroComputers UltiChart LE-5000 digital mapping system serial number (S/N 2247). The unit is capable of recording aircraft heading, miles per hour, altitude (agl), and date and time, location.
The initial download of the data was attempted at the General Services maintenance facility. An initial viewing of the data revealed that the first 180-degree autorotation was started at an altitude of 350 feet. The second 180-degree autorotation, the accident, was started at an altitude 300 feet and the airspeed was slower than 60 knots. The box was then taken to AeroComputers facilities in Oxnard, California, for a complete download. During the inspection of the unit, it was determined that the unit had not been updated and that the compact flash was corrupted. Technicians at AeroComputers were able to successfully download the video and it is attached to the public docket for this report. Recovered data showed that the helicopter averaged a 1,747-foot-per-minute descent in 8 seconds.
The passenger opined that due to the extra weight of a third person in the helicopter, which was on one side, it may have made the recovery more difficult in an emergency situation. He stated that it may be more prudent in the future to have only necessary persons in an aircraft during non-standard flights such as the training exercises we were attempting to perform immediately prior to the incident. He also indicated that having increased safety features for the rear seats, such that exist in the front seats, his injuries may have been lessened.