The Aviation Safety Council （ASC） releases final report on the investigation of a National Airborne Service Corps, Ministry of the Interior （NASC） UH-60M Black Hawk helicopter, number NA-703, during conducted a search and rescue joint training mission, rescuers to fall into the ocean and sustained injury at offshore of Taichung Harbor.

On Jun 30, 2017, the UH-60M helicopter conducted a search and rescue joint training mission. During hoist up rescue process, due to hoist hook inappropriate assembling while doing maintenance process, the hook assembly was separated from the hoist system causing two rescuers to fall into the ocean. One rescuer sustained minor injury and the other sustained serious injury.

According to the Aviation Occurrence Investigation Act of Republic of China （ROC） and the content of Annex 13 to the Convention on International Civil Aviation Organization, the Aviation Safety Council （ASC）, an independent aviation occurrence investigation agency, was responsible for conducting the investigation. The investigation team also included National Airborne Service Corps, Ministry of the Interior.

Findings related to probable causes:

1. During hoist cable replacement maintenance, an unknown external force may led the bearing moved and stuck in the bearing housing when the hook assembly was disassembled
2. When assembling the hook assembly, the mechanic could not properly bottomed the bushing nut to the bearing housing due to the bearing stuck in the bearing housing. A 1.5 mm gap was created between the lower flange bottom surface of the bushing nut and top surface of the bearing housing. The above gap caused the locking screws not properly engaged into the castled slots on the bearing housing.
3. The inspector did not properly check whether the two locking screws were engaged into the castled slots on the bearing housing prior to the completion of the hoist cable replacement.
4. Due to the two locking screws were not properly engaged into the castled slots on the bearing housing, therefore the bearing housing did not lock with the bushing nut. Without lock mechanism, the bearing housing was loosening from the screw threads of bushing nut and separated from the hoist assembly when hook assembly swiveled during hoist retrieving process.

Findings related to the risks:

1. The mechanics and the inspectors neither understood and followed the procedures correctly during assembling nor visually inspected the locking screws were properly engaged into the castled slots on the bearing housing. They misunderstood that the locking screws were properly seated in the castled slots once the cotter pin holes could be seen.
2. The National Airborne Service Corps did not assign a proper quality inspector to perform the hoist maintenance for the occurrence helicopter. The inspector who performed the inspection of the hoist maintenance did not complete the type hoist maintenance training, had limited understanding of the hoist manufacture maintenance manual, and failed to conduct the vital point inspection correctly.
3. Most maintenance manuals adopted by the National Airborne Service Corps （NASC） are in English. The NASC did not establish the English ability requirement and evaluation system of their mechanic.
4. The National Airborne Service Corps （NASC） did not have proper process to integrate/control both technical information from hoist manufacturer and technical manual from aircraft manufacturer regarding the hoist maintenance. The different understanding of how to use the manual existed in NASC different department that disadvantaged the NASC mechanic to use the manual correctly and conduct the training properly.   
5. The National Airborne Service Corps did not record inspection results of vital point onto rescue hoist maintenance log as required by the hoist manufacturer maintenance manual.
6. There are neither Public Aircraft Oversight Act nor regulations related to safety, operations and management of public aircraft. The existing safety standards and management mechanism of public aircraft were all established by the National Airborne Service Corps itself, thus the safety standards and management mechanism of public aircraft might be hindered by the cost, mission requirements or performance consideration.
7. The National Airborne Service Corps established a task force “Aviation Safety Commission” instead of a permanent safety division, because of the proposal of such division made by the Ministry of the Interior was denied during the Central Government Agency reorganization process. After reviewing the job function and operation of the Aviation Safety Commission, it is unable to function effectively as a permanent safety division or external audit agency.
8. There were three National Airborne Service Corps occurrences in the past. The findings related to the probable causes of these occurrence are not only human errors but also systemic issues such as insufficient training, improper management, and lack of safety procedures. The above findings showed that the task force, Aviation Safety Commission, was unable to function effectively and cover the internal safety management and external safety oversight.

Safety Recommendations

To the National Airborne Service Corps, Ministry of the Interior

1. Establish standard procedures and enhance training to prevent the external force damage to the part/assembly from its disassembling to assembling.
2. Ensure all mechanics understand maintenance manual and perform maintenance procedures correctly. Consider to provide mechanics with checklists of complex or easily misunderstanding procedures and vital point inspections. .
3. Enhance training preparations prior to the manufacturer conducting the training to promote effective training result, including: require trainees to pre-study manuals and get familiar with parts diagrams, name and number of parts; prepare diagrams, flow chart or vital point inspections for complex or easily misunderstanding procedures; assign qualified translator or mechanics to assist foreign instructors in course teaching.
4. Evaluate and set requirements for mechanics on adequate English ability to assure procedures understanding and maintenance quality.
5. Review and improve inspectors job assignment procedure and quality control ability.
6. Properly integrate and control the usage of the component maintenance manual and aircraft maintenance manual regarding the hoist maintenance to benefit maintenance practice and training purpose.
7. Enhance the control process of maintenance procedure changes as well as notification of such changes. Activate change management process accordingly when necessary. Provide all related supporting measures and complete required approval process. Lastly, ensure all relevant personnel have common understanding to the scale of change.

To Ministry of Interior

1. Re-exam the organizational structure and operating effectiveness of the task force, Aviation Safety Commission, National Airborne Service Corps. Assist the National Airborne Service Corps, Ministry of the Interior to establish a formal Safety Management Division to enhance internal safety management. 
2. Establish a formal, full time and effective safety oversight system to improve public aircraft aviation safety.

Full Final Report is in Chinese only and available for download at http://www.asc.gov.tw

Sherry Liu, Engineer
Tel: 02-89127388-ext330
Email:sherry@asc.gov.tw