Wahiawa, HI, USA
N632NV
Robinson R44
The pilot and two passengers were in cruise flight in the helicopter when the engine oil light illuminated. The pilot initiated an immediate descent to land and confirmed that the engine continued to produce power (the oil pressure light is one of the indications of an engine failure). As the helicopter approached the ground, the pilot slightly manipulated collective to maintain rotor rpm within limits. The helicopter impacted terrain with some forward speed and slid about 40 ft before coming to a stop. During his postflight examination of the helicopter, the pilot noted oil on the outside of both lower engine inspection panels and on the inside of the engine inspection panel on the pilot's side. The oil level dipstick indicated oil at about the 1/8-inch mark. Review of video from the onboard camera indicated that the red "oil" warning light illuminated in flight, and the oil pressure gauge indicated that the oil pressure had dropped to zero. It also revealed that during the deceleration/flare sequence, the engine rpm dropped to about 80%; however, once the helicopter stabilized on the ground, the engine rpm increased and returned to 102%. According to the R44 Pilot’s Operating Handbook, engine rpm is maintained by a governor, but only above 80%. For the engine rpm to drop to 80% and below, the pilot must manually rotate the throttle. Manual manipulation is not typically required except during start up, shut down, autorotation practice, and emergencies. The handbook also states that the emergency procedure in response to an illuminated oil light is to "land immediately," which the pilot proceeded to do. However, the helicopter did not lose engine power; therefore, there was no need for the pilot to manipulate the throttle. It is possible that, without throttle manipulation, the pilot could have performed a normal landing to a suitable landing area and landed safely under power without damage to the helicopter. A postaccident engine functionality check did not reveal any anomalies; the engine ran for 8 minutes without any apparent oil leaks. However, the next day, fresh oil was noted under the engine oil filter. Further examination revealed that the torque required to rotate the oil filter was significantly less than normal. In addition, the threaded fitting that the filter threads onto the adapter was about 2 threads in, and the filter cavity was empty of any oil. The loss of oil in flight was likely a result of the loose oil filter adapter.
On September 18, 2018, about 0815 Hawaiian standard time, a Robinson R44 Raven I helicopter, N632NV, was substantially damaged when it was involved in an accident near Wahiawa, Hawaii. The pilot and two passengers were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 136 commercial air tour flight. The flight originated from the Daniel K Inouye International Airport (HNL), Honolulu, Hawaii, about 0745. The pilot reported that, during preflight, the oil level was at 9 quarts and the fuel level was at 11 gallons. A note from company maintenance indicated that the 50-hour inspection, as well as a repair to the engine cowl, had been completed the previous night. The helicopter departed HNL. While the helicopter was in cruise flight about 2,200 ft above ground level, the engine oil light illuminated red and stayed illuminated for the rest of the flight. There were no other indications in the cockpit, but the pilot began to execute the emergency procedure of landing immediately. The pilot noted that the helicopter did not lose engine power and he did not need to adjust the throttle or enter autorotation (an oil pressure light is one of the indications of an engine failure). About 4 to 7 seconds after the oil light illuminated, he noted minor fluctuations in engine rpm; however, the allowable limits were never exceeded. The pilot then noted a “major spike” and overspeed of the engine rpm greater than 110%; he later realized that it was the main rotor building and overspeeding. The pilot stated that he continued the descent and, as he approached closer to the ground, began to decelerate as the altitude lowered. As the helicopter neared the end of the descent, the pilot raised the collective; however, the low rotor rpm light illuminated, and the low rotor rpm horn annunciated. He stated that he either kept the collective where it was or slightly lowered the collective and tried to lower the tail into a steeper flare. After the flare, he brought the helicopter to a mostly level attitude and tried to cushion the landing by raising the collective as the helicopter neared touchdown. The helicopter impacted terrain at about 40 knots, after which it slid about 40 ft. During the postimpact sequence, the left skid separated, and the helicopter rotated about 90°. During his postflight inspection, the pilot noted oil on the outside of both lower engine inspection panels, which continued down the tailboom and over the vertical stabilizer and tail rotor. A large quantity of oil was also found on the inside of the engine inspection panel on the pilot's side. The oil level dipstick indicated oil at about the 1/8-inch mark. A review of a video obtained from an onboard camera indicated that the red "oil" warning light illuminated in flight when the helicopter was about 2,500 ft mean sea level. The oil pressure gauge indicated that the oil pressure dropped to zero. During the descent, the manifold pressure indicated 12 inches of manifold pressure and remained at about the same power setting for the duration of the descent; the engine rpm and rotor rpm fluctuated in small percentages (98%-105%). The helicopter flared about 40-70 ft above ground level, and the main rotor was overspeeding. During the deceleration/flare sequence, the engine rpm dropped to about 80%; however, once the helicopter stabilized on the ground, the engine rpm increased and returned to 102%, which is within the normal operating range. The R44 Pilot's Operator Handbook states, in part, the following: "The governor maintains engine RPM by sensing changes and applying corrective throttle inputs through a friction clutch which can be easily overridden by the pilot. The governor is active only above 80% engine RPM and can be switched on or off using the toggle switch on the end of the right seat collective.” The handbook also states that the “electronic engine governor makes minor throttle adjustments by rotating the twist grip to maintain RPM within power-on limits. Manual manipulation of the twist grip is not typically required except during start up, shut down, autorotation practice, and emergencies." In addition, the emergency procedure for an illuminated oil light states, in part, that the oil light "…indicates loss of engine power or oil pressure. Check engine tech for power loss. Check oil pressure gage and, if pressure loss is confirmed, land immediately." An engine functionality check after the accident was performed. About 7.5 quarts of engine oil were added to the engine, which brought the total oil level to 9 quarts as depicted on the engine dip stick. The engine started normally and ran for 8 minutes with no apparent oil leaks or anomalies detected. The next day, maintenance personnel noticed fresh oil in a plastic pan that had been placed under the forward area of the engine near the engine oil filter. As the mechanic attempted to remove the oil filter, he noticed that it required significantly less resistance to rotate than normal. Once the filter was removed, the mechanic noticed that the threaded fitting that the filter threads onto the adapter was only 2 threads in, and the filter cavity was empty of any oil.
Loss of oil in flight as a result of a loose oil filter adapter which resulted in the pilot initiating an immediate landing to an open field. Contributing to the accident was the pilot's manipulation of the throttle that led to a reduction in rotor rpm, which resulted in his inability to perform a normal landing.
Source: NTSB Aviation Accident Database
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