The Aviation Safety Council （ASC） releases final report on investigation of  an Emerald Pacific Airlines （Emerald Pacific）Bell 206B3（Bell 206） helicopter, registration number B-31019, was loss of engine power and forced landing during insulator washing of high voltage power lines in Changhua area.

On December 18, 2014, Emerald Pacific, a Bell 206 helicopter, took off from temporary airfield to perform insulator washing of high voltage power lines with water in the air in Changhua area. The aircraft was loss of engine power at the last trip and forced landing on grass field. One pilot and one hydraulic nozzle operator aboard were suffered minor injuries. The helicopter was suffered substantial damage.

The ASC is an independent agency responsible for civil aviation, public aircraft and ultra-light vehicle occurrences investigation. According to the Republic of China Aviation Occurrence Investigation Act and referencing to the related content of Annex 13 to the Convention of International Civil Aviation Organization （ICAO）, the ASC launched an occurrence investigation by law. The organization or agency been invited to join the investigation team also included: Civil Aeronautics Administration of Ministry of Transportation and Communications （CAA）, Emerald Pacific Airlines, Transportation Safety Board （TSB）/ Canada, National Transportation Safety Board （NTSB） and Rolls-Royce Corporation / USA. The final report was reviewed and approved by ASC's 40th Council Meeting on December 29, 2015.

Findings related to probable causes:

1. The aircraft loss of engine power was determined the separation of the 3rd stage blade of engine compressor. The probable causes of blade separation are: （1） an airfoil fracture initiating in a corrosion pit, which then progressed in high cycle fatigue until the blade separated in overload, or （2） blade tip rub caused by delamination of the case plastic lining due to corrosion underneath the vane outer band.
2. The probable cause of the corrosion of the compressor is the improper compressor maintenance during operation in a corrosive environment. The M250-C20 Series engine Operation and Maintenance Manual contains warnings that: salt laden humidity and chemicals will corrode compressor blades and vanes and cause them to fail.

Findings related to risk

1. The aircraft operator was not aware that the whole Taiwan island is classified as the severe corrosion operating environment by the Operation and Maintenance Manual and did not follow the manual to perform a water rinse of the compressor after daily flight which allowed the contamination accumulated on the compressor and resulted in corrosion to the compressor.
2. The limit of engine shutdown period prescribed in the aircraft operator's continuous airworthiness maintenance program was not compliance with the engine manufacturer manual. The aircraft operator did not follow preservation procedure and allow the engine shutdown period frequently exceeded 5 days limit. Engine shutdown in long period without proper preservation in corrosive environment would cause the corrosion on the compressor.
3. The aircraft operator did not follow the procedures to inspect the erosion and corrosion of the compressor blades and vanes when performing the 300 Hour inspection of compressor. It missed the chance to detect the serious corrosion of the compressor during the last time inspection before occurrence.
4. The line maintenance personnel was lack of sufficient knowledge and experience of the engine maintenance.
5. The training program related to engine maintenance of the aircraft operator was inadequate and resulted in the lack of expertise of the line maintenance staff in engine maintenance.
6. The oversight of Civil Aeronautics Administration was unable to identify and/or rectify the operator's safety deficiencies including engine maintenance incompliance with appropriate maintenance manual, insufficient training of maintenance personnel, discrepancy of maintenance program, and not properly updating the engine maintenance manual.
7. The aircraft operator did not follow the Operation and Maintenance Manual to adjust the interval of compressor 300 Hour inspection based on the corrosion condition of the compressor.
8. The aircraft operator once exceeded the interval of 300 Hour inspection and 1,750 Hour inspection prescribed in the Operation and Maintenance Manual.
9. The aircraft operator did not properly update and manage the Operation and Maintenance Manual. It would lead to maintenance personnel performing the tasks without the latest updated information.
10. The Civil Aeronautics Administration's maintenance inspector was lack of understanding of aircraft operator's engine maintenance procedure. That deprived the inspector of an opportunity to recognize the operator's maintenance defects during supervision process.

Safety Recommendations
To Emerald Pacific Airline:

1. Enhance the engine maintenance training for maintenance personnel, and ensure the engine maintenance personnel clearly understand the contents of Operation and Maintenance Manual and the job cards.
2. Reevaluate the company's maintenance capability of 300 Hour inspection on Rolls-Royce 250-C20J engine to ensure the inspections to be performed properly.
3. Review and revise the company's continuous airworthiness maintenance program to ensure the contents complied with the engine manufacturer's standard.
4. Enhance the control mechanism of the manuals updating and job cards management to ensure latest maintenance information timely  available for maintenance personnel.
5. Enhance the operation control of performing maintenance and inspection program to ensure the inspection intervals will comply with the engine Operation and Maintenance Manual.

To Civil Aeronautics Administration:

1. Require Emerald Pacific Airlines, to provide proper engine maintenance training for maintenance personnel and ensure the engine maintenance personnel clearly understand the contents of Operation and Maintenance Manual and the job cards.
2. Require Emerald Pacific Airlines, to reevaluate the company's maintenance capability of 300 Hour inspection on Rolls-Royce 250-C20J engine to ensure the inspections to be performed properly.
3. Require Emerald Pacific Airlines, to revise the company's continuous airworthiness maintenance program to ensure the contents are complied with the engine manufacturer's standard, and to enhance control mechanism of the manuals updating and job cards management to ensure latest maintenance information timely  available for maintenance personnel.
4. Review the maintenance supervision of general aviation to enhance the capability of identifying and addressing the systemic failure of the aircraft operator. And require the general aviation maintenance inspectors to be knowledgeable about the type aircraft and engine operated by the assigned operator to identify the maintenance discrepancies during supervision.

Full investigation report is available for download at http://www.asc.gov.tw

Sherry Liu, Engineer
Tel: 89127388-330
Email:sherry@asc.gov.tw