Accident Details
On September 18, 2018, at approximately 0815 Hawaiian standard time, a Robinson R44 Raven I helicopter, registration N632NV, was substantially damaged during an accident near Wahiawa, Hawaii. The helicopter was operating as a Title 14 Code of Federal Regulations Part 136 commercial air tour flight. The pilot and two passengers were not injured. The flight had originated from Daniel K Inouye International Airport (HNL), Honolulu, Hawaii, about 0745.
Preflight Information
During preflight, the pilot reported an oil level of 9 quarts and a fuel level of 11 gallons. A note from company maintenance indicated that the 50-hour inspection and a repair to the engine cowl had been completed the previous night.
In-Flight Events
While cruising at about 2,200 ft above ground level, the engine oil light illuminated red and remained illuminated for the remainder of the flight. No other cockpit indications were present. The pilot initiated emergency procedures to land immediately. The helicopter did not lose engine power, and the pilot did not need to adjust the throttle or enter autorotation. Approximately 4 to 7 seconds after the oil light illuminated, minor fluctuations in engine rpm were observed within allowable limits. Subsequently, a major spike and overspeed of engine rpm greater than 110% occurred, which the pilot later identified as the main rotor overspeeding.
The pilot continued the descent and began decelerating as the altitude lowered. Near the end of the descent, the pilot raised the collective, but the low rotor rpm light illuminated and the low rotor rpm horn sounded. The pilot then either kept the collective position or lowered it slightly and attempted to flare by lowering the tail. After the flare, the helicopter was brought to a mostly level attitude, and the pilot raised the collective to cushion the landing. The helicopter impacted terrain at about 40 knots, sliding approximately 40 ft. During the postimpact sequence, the left skid separated, and the helicopter rotated about 90°.
Postaccident Findings
During postflight inspection, the pilot observed oil on the exterior of both lower engine inspection panels, extending along the tailboom and over the vertical stabilizer and tail rotor. A large quantity of oil was found on the interior of the engine inspection panel on the pilot's side. The oil level dipstick indicated oil at approximately the 1/8-inch mark.
A review of onboard camera video showed the red oil warning light illuminated at about 2,500 ft mean sea level, and the oil pressure gauge indicated zero pressure. During the descent, manifold pressure remained at 12 inches, and engine and rotor rpm fluctuated between 98% and 105%. The helicopter flared at about 40 to 70 ft above ground level with the main rotor overspeeding. During the deceleration and flare, engine rpm dropped to about 80%; after the helicopter settled on the ground, engine rpm returned to 102%, within normal operating range.
Aircraft Information
The R44 Pilot's Operator Handbook states that the governor maintains engine rpm by sensing changes and applying corrective throttle inputs through a friction clutch, which can be overridden by the pilot. The governor is active above 80% engine rpm. The handbook also states that manual manipulation of the twist grip is not typically required except during start up, shut down, autorotation practice, and emergencies. Emergency procedures for an illuminated oil light indicate that it signifies loss of engine power or oil pressure; the pilot should check engine tech for power loss, check the oil pressure gauge, and land immediately if pressure loss is confirmed.
Engine Examination
An engine functionality check after the accident involved adding about 7.5 quarts of engine oil, bringing the total to 9 quarts on the dip stick. The engine started normally and ran for 8 minutes with no oil leaks or anomalies. The next day, maintenance personnel found fresh oil in a pan placed under the forward area of the engine near the engine oil filter. When the mechanic attempted to remove the oil filter, significantly less resistance than normal was noted. Upon removal, the threaded fitting onto which the filter threads had only two threads engaged, and the filter cavity was empty of oil.