Accident Details
On May 8, 2013, about 1520 Hawaiian standard time, a Robinson R22 Beta helicopter, registration N5ZK, was substantially damaged when it collided with an unoccupied parked automobile following a total loss of engine power while maneuvering over Honolulu, Hawaii. HLM Aviation owned the helicopter, and Hawaii Pacific Aviation (doing business as Mauna Loa Helicopters) operated it under 14 Code of Federal Regulations Part 91. The certified flight instructor (CFI) was not injured; the passenger sustained minor injuries. The local aerial observation flight departed from Honolulu International Airport about 1455. Visual meteorological conditions prevailed, and no flight plan had been filed.
Engine Failure and Autorotation
The CFI stated the purpose of the flight was to orbit the helicopter over an area known as Punchbowl, about five nautical miles south of the airport. She departed as planned, proceeded to Punchbowl, and completed two orbits before slowing the helicopter to about 35 knots to facilitate the passenger's aerial photography. While maneuvering about 3,000 feet above ground level, the engine suddenly experienced a total loss of power, followed immediately by activation of the low rpm light and horn. In response, the CFI lowered the collective and entered an autorotation, maintaining 60 knots. She maneuvered to land on a street and began the flare at about 40 feet agl. The helicopter touched down on the road and skidded into a parked automobile.
Post-Accident Examination
A Federal Aviation Administration (FAA) inspector performed a post-accident examination of the helicopter. The mixture cable was fracture-separated from the mixture bellcrank control arm on the carburetor. The bellcrank was positioned near the idle cutoff position, rather than the full-rich position. The spring did not drive the arm to the full rich position per design. The inspector noted that the spring was not correctly connected to the mixture arm. The helicopter's maintenance manual states that during inspection the mechanic must "Verify spring moves arm to full rich position."
Maintenance Findings
The mechanic who routinely maintained the helicopter stated that his company completed a 2,200-hour airframe overhaul on April 22, 2013, equating to about 16 flight hours prior to the accident. He recalled that after the overhaul, he inspected the helicopter, which included tracking and balancing of the main rotor, tail rotor, and engine. The mechanic accompanied the FAA inspector during the post-accident examination. They determined that the mixture arm assembly was improperly rigged. The mixture-to-bellcrank hardware stackup was incorrect and did not allow the mixture cable to move freely, and the spring was installed so that the arm was driven to the idle cutoff position. The mechanic opined that repeated stress on the mixture cable caused it to break after a number of operation cycles. When the failure occurred, the bellcrank spring, designed to force the mixture to full rich, instead cut off the fuel by pulling the mixture to idle cutoff. The mechanic remarked that the rigging of the carburetor was accomplished by an apprentice under his supervision. The mechanic did not visually observe the misrigging and reported that if he had performed a tactile inspection, he would have detected the error.