Robinson Helicopter R22 BETA N5ZK accident near Honolulu, Hawaii

Probable cause

The mechanic’s failure to properly inspect the helicopter following maintenance performed by an apprentice, which resulted in a total loss of engine power due to the improper rigging of the mixture control assembly.

NTSB analysis

The pilot reported that, while he was maneuvering the helicopter about 3,000 feet above ground level (agl), the engine suddenly experienced a total loss of power, which was immediately followed by the activation of the low rotor rpm light and horn. In response to the engine failure, the pilot lowered the collective and entered an autorotation. She began to flare the helicopter at an altitude of about 40 feet agl. The helicopter touched down on a road and skidded into a parked automobile.

A postaccident examination of the helicopter revealed that the mixture cable had fracture-separated from the mixture bellcrank control arm located on the carburetor. The bellcrank was positioned near the idle/cutoff position, and the spring was inserted in the wrong direction. The helicopter airframe had undergone an overhaul about 16 hours of flight time before the accident, and, during that overhaul, a mechanic's apprentice installed the mixture hardware. The apprentice improperly rigged the mixture-to-bellcrank hardware, which prevented the mixture cable from moving freely. The repeated stress on the mixture cable resulted in it breaking after a number of operation cycles. When the failure occurred, the bellcrank spring, which is designed to force the mixture to the full-rich position, instead pulled the mixture to the idle/cutoff position, which cut off the fuel. The mechanic overseeing the apprentice reported that he did not visually observe the misrigging and that, if he had performed a tactile inspection, he would have detected the error.

Text from the NTSB. Open the NTSB docket for WPR13LA222 for the full record.