Saturday, February 16, 2019

Loss of Engine Power (Partial): Robinson R44 II, N488AS, accident occurred July 02, 2017 in Bella Vista, Shasta County, California

The National Transportation Safety Board did not travel to the scene of this accident.

Additional Participating Entities:

Federal Aviation Administration / Flight Standards District Office; Sacramento, California
Lycoming Engines; Williamsport, Pennsylvania
Robinson Helicopter Company; Torrance, California

Aviation Accident Final Report - National Transportation Safety Board:

Investigation Docket - National Transportation Safety Board:

Location: Bella Vista, CA
Accident Number: WPR17LA140
Date & Time: 07/02/2017, 1715 PDT
Registration: N488AS
Aircraft: Robinson R44
Aircraft Damage: Substantial
Defining Event: Loss of engine power (partial)
Injuries: 2 Serious, 2 Minor
Flight Conducted Under: Part 91: General Aviation - Personal 


The commercial pilot reported that, while making a left descending turn in the helicopter about 75 to 100 ft above a pond to set up for landing to a field, he heard three "pops," followed by the low rotor horn sounding and the caution light illuminating. The pilot assumed that the engine had lost power, and he immediately and abruptly lowered the collective, pulled aft on the cyclic, and rolled the throttle to full open. To avoid obstructions, he steepened the right turn. Realizing that the rotor rpm was below 50% and that the helicopter would not reach the field, he subsequently landed the helicopter on the pond; it then sank. The pilot was unsure if the engine was running or not.

Postaccident airframe and engine examinations revealed no evidence of any preaccident mechanical failures or malfunctions that would have precluded normal operation. The reason for the partial loss of engine power could not be determined.

Probable Cause and Findings

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
A partial loss of engine power during low-altitude maneuvering for reasons that could not be determined because postaccident examinations of the engine and airframe revealed no evidence of any preaccident mechanical malfunctions or failures that would have precluded normal operation.


Not determined
Not determined - Unknown/Not determined (Cause)

Factual Information

History of Flight

Maneuvering-low-alt flying
Loss of engine power (partial) (Defining event)

Abrupt maneuver
Attempted remediation/recovery


Off-field or emergency landing

On July 2, 2017, about 1715 Pacific daylight time, a Robinson Helicopter Company R44 II helicopter, N488AS, landed in a pond near Bella Vista, California. The commercial pilot and one passenger sustained minor injuries; two passengers sustained serious injuries. The helicopter was substantially damaged. The helicopter was registered to Aero Leasing Inc. and operated by Air Shasta Rotor & Wing Inc. under the provisions of Title 14 Code of Federal Regulations Part 91, as a personal flight. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from Redding, California about 1705 and was destined for a private residence in Bella Vista. 

The pilot reported that the purpose of the flight was to attend a birthday party on private property, and that he would be giving rides. When the flight arrived at its destination, the pilot flew over the property and made a left descending turn into the wind about 75-100 ft above ground level. The pilot centered over a pond at an airspeed of 70 knots indicated with the intention of making a right turn to setup for landing into the wind at the predetermined landing zone. As he started the right turn, he heard 3 "pops", followed by the low rotor horn sounding and the caution light illuminated. The pilot assumed that the engine had lost power and he immediately and abruptly lowered the collective, pulled aft on the cyclic and rolled the throttle to full open. The nose came up and to avoid obstructions, he steepened the right turn. Realizing that he now did not have enough momentum to reach the open field, and that the rotor RPMs were below 50%, he decided to land in the pond. During the descent, the tail struck a tree about 60 ft above the pond which pitched the helicopter nose low. The pilot pulled aft on the cyclic and positioned the collective full down. About 10-15 ft above the water, he pulled full collective and the helicopter hit the water in about a 5o nose low attitude, and slightly left side low. The helicopter subsequently sank.

The pilot believed that the helicopter was traveling about 35-45 mph when it hit the water, and he was unsure if the engine was running or not.

Pilot Information

Certificate: Commercial
Age: 50, Male
Airplane Rating(s): None
Seat Occupied: Front
Other Aircraft Rating(s): Gyroplane; Helicopter
Restraint Used: 3-point
Instrument Rating(s): None
Second Pilot Present: No
Instructor Rating(s): None
Toxicology Performed: No
Medical Certification: Class 2 With Waivers/Limitations
Last FAA Medical Exam: 06/30/2017
Occupational Pilot: Yes
Last Flight Review or Equivalent:
Flight Time:  (Estimated) 502 hours (Total, all aircraft), 350 hours (Total, this make and model), 350 hours (Pilot In Command, all aircraft), 1 hours (Last 24 hours, all aircraft)

The 50-year-old pilot held a commercial pilot certificate with ratings for helicopter and gyroplane. His most recent second-class medical certificate was issued on June 24, 2017, with the limitation the he must have available glasses for near vision. The pilot reported a total flight time in all aircraft of 502 hours. A total flight time of 350 hours had been accumulated in the make/model helicopter involved in the accident.

Aircraft and Owner/Operator Information

Aircraft Make: Robinson
Registration: N488AS
Model/Series: R44 II
Aircraft Category: Helicopter
Year of Manufacture: 2008
Amateur Built: No
Airworthiness Certificate: Normal
Serial Number: 12538
Landing Gear Type: Ski;
Seats: 4
Date/Type of Last Inspection: 06/01/2017, Annual
Certified Max Gross Wt.: 2500 lbs
Time Since Last Inspection: 26 Hours
Engines: 1 Reciprocating
Airframe Total Time: 2143.82 Hours at time of accident
Engine Manufacturer: Lycoming
ELT: Not installed
Engine Model/Series: IO-540-AE1A5
Registered Owner: Aeroleasing Inc
Rated Power: 205 hp
Operator: On file
Operating Certificate(s) Held: Pilot School (141); Rotorcraft External Load (133); On-demand Air Taxi (135)

The helicopter, serial number 12538, was manufactured in 2008 and was equipped with an IO-540-AE1A5, six-cylinder, direct drive, horizontally opposed, normally aspirated (fuel injected), internal combustion engine rated at 205 horsepower. The last annual inspection was accomplished on June 1, 2017, at a total airframe time of 2,117.74 hours. At the same time, the engine was signed off for a 100 hour inspection. Total time since new for the engine, that was installed in the airframe on June 5, 2008, was 2,117.74 hours. At the time of the accident, both the airframe and engine had accumulated a total time of 2,143.82 hours.

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual Conditions
Condition of Light: Day
Observation Facility, Elevation: KRDD, 505 ft msl
Distance from Accident Site: 11 Nautical Miles
Observation Time: 1653 PDT
Direction from Accident Site: 9°
Lowest Cloud Condition: Clear
Visibility:  10 Miles
Lowest Ceiling: None
Visibility (RVR):
Wind Speed/Gusts: 14 knots /
Turbulence Type Forecast/Actual: /
Wind Direction: 150°
Turbulence Severity Forecast/Actual: /
Altimeter Setting: 29.8 inches Hg
Temperature/Dew Point: 38°C / 13°C
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: Redding, CA (RDD)
Type of Flight Plan Filed: None
Destination: Redding, CA (RDD)
Type of Clearance: None
Departure Time: 1700 PDT
Type of Airspace: Class G

The nearest official weather reporting facility was in Redding, California, about 11 nautical miles north of the accident site. 

At 1653, the sky was clear, and visibility was 10 miles. The temperature was 100o F, dew point was 55o F. The altimeter setting was 29.80 in. Hg.

Wreckage and Impact Information

Crew Injuries: 1 Minor
Aircraft Damage: Substantial
Passenger Injuries: 2 Serious, 1 Minor
Aircraft Fire: None
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries: 2 Serious, 2 Minor
Latitude, Longitude:  40.669722, -122.178333 (est)

Investigators from the Federal Aviation Administration (FAA), Robinson Helicopter Company (RHC), and Lycoming Engines examined the wreckage at the operator's facility. A full report is contained within the public docket for this accident.


The collective and cyclic frictions were found off, the governor was on, the clutch switch was engaged, and the mixture control knob was positioned in the full rich position. The collective was positioned in a nearly full up position. The pedals were positioned with the left pedal forward of the right. The transponder and governor circuit breakers were found up (out). The filaments of all the warning lights appeared normal. The engine and rotor rpm gages were on the bottom peg; the console remained attached.

Both fuel cells remained intact and both fuel caps were secured on their necks. The fuel vent lines were found to be clear. The main fuel shutoff valve was on, and the fuel selector knob turned freely. The gascolator screen had a small amount of lint on the screen. Approximately 28 gallons of fuel mixed with water was removed from the tanks. 

The Sprag Clutch bearing rotated smoothly and operated properly. The distance between the clutch actuator assembly anti-rotation scissors was 1.1". All four V-belts were intact but were displaced from their grooves. 

The main rotor mast appeared straight, however the whole shaft assembly had a slight forward tilt. The main rotor gearbox was intact and secure on its mounts. The forward flex coupling was straight and intact. The intermediate flex coupling was intact but exhibited a bend and score marks from contact with the upper fan scroll. There was continuity and freedom of rotation in the drive line from the main rotor shaft to the disconnect in the tail rotor drive shaft. Continuity and freedom of rotation was noted in the tail rotor drive shaft from the disconnect to the tail rotor blades. The aft flex coupling was intact and straight. 

The tail rotor gearbox was intact. The teetering bolt and both coning bolts on the main rotor head were secure. There was a defined crush line across the elastomeric portion of both teeter stops. The droop stops, and droop stop tusks were in place. 

Main rotor flight control continuity was confirmed. All main rotor flight control connections were found secure. 

The right pedal Push-Pull Tube was disconnected near the bellcrank end of the tube. The rod end was pushed through the fiberglass chin of the helicopter by the impact. The right pedal Push-Pull Tube remained secured to the Pedal Assembly. All other tail rotor flight control connections were found secure. The C121-17 Push-Pull Tube was intact. The tail rotor pitch change slider was free to slide along the tail rotor gearbox output shaft.


No evidence of contact between the starter ring gear and oil coolers was found. The forward side of the fan scroll was crushed and fractured from impact. A light score mark was visible on the inside of the fan scroll where the fan had contacted the forward side of the scroll. The paint on the outer lips of the forward and aft sides of the fan was rubbed off from contact with the scroll. The upper scroll had a jagged tear and score marks from contact with the intermediate flex plate. The A185-1 bracket was found loose with one end detached. Rivet holes on the detached end were visibly elongated. 

The crankshaft rotated easily by hand utilizing the cooling fan. The bottom spark plugs were removed, and "thumb" compression was observed in proper order in all six cylinders. Valve train continuity was established, and normal lift action was observed at each rocker assembly. Clean, uncontaminated oil was observed at the exposed rockerbox areas. Mechanical continuity was established throughout the rotating group and accessory section during hand rotation of the crankshaft. The combustion chambers of each cylinder were viewed through the spark plugs holes utilizing a borescope. The chambers were undamaged, with no evidence of foreign object ingestion or detonation was observed. The spark plugs, although contaminated with postaccident water emersion displayed coloration consistent with normal wear signatures.

The left and right magnetos remained securely clamped at their respective mounting pads. The ignition harness was secure at each magneto. Due to water emersion, magneto to engine timing could not be ascertained. The magnetos were removed for further examination. A set of right magneto contacts that had been removed and replaced prior to the accident were also retained.

The magnetos were manually rotated, and both produced inconsistent spark. Follow-up examinations of the magnetos at Robinson Helicopter Company and Continental Motors Inc. discovered corrosion on some parts, which was likely due to the time between removal of the helicopter from the water and the examinations. After cleaning the parts, satisfactory test results were obtained. (Complete examination reports are contained in the public docket)

NTSB Identification: WPR17LA140
14 CFR Part 91: General Aviation
Accident occurred Sunday, July 02, 2017 in Bella Vista, CA
Aircraft: ROBINSON R44, registration: N488AS
Injuries: 2 Serious, 2 Minor.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed. NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

On July 2, 2017, about 1715 Pacific daylig
ht time, a Robinson Helicopter Company R44, N488AS, crashed into a pond near Bella Vista, California. The commercial pilot and one passenger sustained minor injuries; two passengers sustained serious injuries. The helicopter sustained substantial damage. The pilot was operating the helicopter under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The local personal flight departed Redding, California, about 1700. Visual meteorological conditions prevailed, and no flight plan had been filed.

The pilot reported that he was making a low pass over a pond. As he pulled up and initiated a turn, the engine sputtered. The pilot made a 180° turn toward the shoreline as he initiated an autorotation. The helicopter could not make it to shore, and the pilot landed in the water.

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