Summary
On October 2, 2015, at approximately 11:13 JST, an Aérospatiale AS332L1 rotorcraft, registration JA9678, operated by Aero Asahi Corporation, was conducting external cargo sling operations in Itoigawa City, Niigata Prefecture, Japan. During a flight from the concrete unloading point back to the cargo sling point, the operator unintentionally released the lock on the red cargo hook, causing the empty concrete bucket to fall. No injuries or damage to the aircraft or ground property occurred.
Factual Information
Flight History
The helicopter was equipped with two cargo hooks, colored red and yellow. The operator and captain had visually confirmed that the bucket was slung on the red hook before and after unloading the ready-mixed concrete. The operator noticed that the yellow hook, which was not carrying any load, was locked. To reduce ground staff work, the operator decided to release the lock on the yellow hook during flight. The operator informed the captain of an intention to release a hook lock but did not specify which hook. Operating the switch box, the operator mistakenly released the lock on the red hook, causing the bucket to drop into a mountain forest along the flight route.
Personnel
The captain, aged 38, held a commercial pilot certificate and type rating for the SA330. The operator, aged 51, had started cargo transport work for the company in July 1992.
Aircraft and Equipment
The aircraft, an Aérospatiale AS332L1 (serial number 2231, manufactured February 18, 1988), had a valid certificate of airworthiness. The cargo hooks and switch box, developed jointly by transport companies, had been in use since February 2015. The switch box panel and caution lights were color-coded to prevent confusion. The locks on the hooks automatically engaged under load (approximately 34 kg or more) or from external impact. No abnormalities were found in the equipment's functioning.
Operational Procedures
The company had provided manuals and educated personnel on operating the cargo hooks and switch box. However, specific procedures for timing of operations and mutual confirmation between captain and operator had not been stipulated for tasks involving the switch box.
Analysis
The investigation determined that the operator had likely intended to release the lock on the yellow hook but mistakenly operated the lock release for the red hook. This error was probable because the operator did not visually confirm the hook color and lacked mutual confirmation with the captain. The absence of a stipulated operational procedure for the use of the switch box was considered a contributing factor.