Aviation safety investigations & reports

Rescue hoist cable failure involving AS 350 B3, VH-UAH 1 km south west of Bulga New South Wales, 5 February 2020

Investigation number:
AO-2020-013
Status: Completed
Investigation completed
Phase: Final report: Dissemination Read more information on this investigation phase

Final

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What happened

On 4 February 2020, an Airbus Helicopters AS 350 B3 was being operated in support of New South Wales National Parks and Wildlife Service activities. Winching of personnel and equipment was being conducted when the operating crewman detected a technical issue with the load cable of the hoist system fitted to the helicopter. The outer strands of the cable toward its termination into the hook assembly had loosened in respect of the inner core.

During a subsequent hoist operation to restore the cable integrity, the cable fractured at the hook assembly while under load, releasing the weight bag and hook assembly to the ground. There was no damage to the helicopter or injuries to personnel.

What the ATSB found

The ATSB found that variations in the operator’s stowage practices over an extended period of winching operations led to inadequate compression of the hook assembly and subsequent wear to the load cable. The wear damage was due to vibration and movement of the hook assembly during periods of helicopter operation. This led to a significant reduction in the cross-sectional area of the cable, fatigue and fracture of the strands and an associated reduction in cable strength.

It is likely that specific post-flight inspection requirements for the Breeze Eastern rescue hoist required in the Civil Aviation Safety Authority (CASA) Airworthiness Directive AD/SUPP/10 were not being adequately completed by the operator. The inspections were targeted at minimising wear damage to the load cable by ensuring correct stowage of the hook assembly at the end of each flight.

Finally, the operator’s method of cycle counting during operation of the rescue hoist led to an accumulation of cycles that significantly exceeded the helicopter manufacturer’s recommended life-limit. That exceedance probably compounded the level of wear damage sustained to the load cable.  

What has been done as a result

The New South Wales National Parks and Wildlife Service (ParkAir) implemented a range of pro‑active safety actions since the occurrence, including:

  • In July 2020, ParkAir provided Breeze-Eastern Flight Line maintenance training for all staff including pilots, maintainers and rescue hoist crewman.
  • A measurement gauge is now used by crewman to determine whether the hoist has adequate compression in accordance with the pre- and post-flight requirements listed within CASA Airworthiness Directive AD/SUPP/10.
  • In January 2021, a revision of the ParkAir Flight Manual Supplement was accomplished to ensure cable inspection procedures requirements are now completed in accordance with CASA Airworthiness Directive AD/SUPP/10.
  • ParkAir have adopted the more conservative Airbus Helicopters method for hoist cycle counting and all hoist cables now have a 500 cycle life-limit.

Additionally, as a direct result of this occurrence and the release of ATSB’s Safety Advisory Notice SAN-2020-013-001, the following pro-active safety advice was released by organisations responsible for the design, manufacture, and regulation of helicopter rescue hoist systems:

  • Breeze-Eastern Service Information Letter (SIL 14 Maintenance) Breeze-Eastern Rescue Hoist Maintenance & Flight Line Inspections for BL-29700 Series, release date 6 April 2020
  • CASA Airworthiness Bulletin (AWB) 25-034 Helicopter Rescue Hoist Wire Rope – Wear, Fatigue and Failure, release date 22 April 2020
  • Airbus Helicopters Safety Information Notice (SIN) 3507-S-25 Fatigue failure of a BREEZE 450 Lbs hoist cable, release date 4 June 2020
  • European Aviation Safety Agency (EASA) Safety Information Bulletin (SIB) 2020-11 Helicopter Rescue Hoist Cable Failure, release date 11 June 2020.

Safety message

The ATSB advises all helicopter operators and flight crew involved in rescue hoist operations to review their current operational practices to ensure hoist operation and hook stowage are in accordance with the manufacturers’ published procedures.

In addition, it is recommended that the pre- and post-flight inspection requirements of the hook and cable assembly, along with any recurring scheduled maintenance of the hoist system are closely reviewed, to ensure that they are completed in accordance with the manufacturers’ instructions. Improper stowage of the hoist hook assembly can lead to excessive movement and accelerated wear of the cable, which if undetected, could have a fatal outcome.

Should any load cable exhibit an increased frequency of outer strand loosening requiring a condition operation, operators should be particularly mindful to check for narrowing or ‘necking’ of the cable at the ball end within the swivel hook assembly. This can signify that the cable has become damaged due to extreme wear and may no longer be safe to use.

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The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Glossary

Sources and submissions

Summary

The ATSB is investigating a cable failure from a rescue hoist fitted to an Airbus AS 350 helicopter, registered VH-UAH, Bulga, NSW, on 5 February 2020. 

The helicopter crew were conditioning the cable during the conduct of maintenance on the rescue hoist when the cable failed. There were no injuries.

As part of the investigation, ATSB investigators will interview the crew, examine the rescue hoist and fractured cable, and collect other evidence including maintenance records and technical data.

Should any safety critical information be discovered at any time during the investigation, the ATSB will immediately notify operators and regulators so appropriate and timely safety action can be taken.

A final report will be published at the conclusion of the investigation.

Safety Issue

Go to AO-2020-013-SI-01 -

Compliance with AD SUPP 10

It is likely that specific post-flight inspection requirements for the Breeze Eastern rescue hoist listed in Airworthiness Directive AD/SUPP/10 were not adequately completed by the operator. The inspections were targeted at ensuring correct stowage of the hook assembly at the end of each flight.

Safety issue details
Issue number: AO-2020-013-SI-01
Status: Closed – Adequately addressed
General details
Date: 05 February 2020   Investigation status: Completed  
  Investigation level: Defined - click for an explanation of investigation levels  
Location   (show map): 1 km south west of Bulga   Investigation phase: Final report: Dissemination  
State: New South Wales   Occurrence type: Infrastructure - Other  
Release date: 21 October 2021   Occurrence category: Serious Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer Airbus Helicopters  
Aircraft model AS 350 B3  
Aircraft registration VH-UAH  
Serial number 7861  
Operator Aviation Utilities Pty Ltd  
Type of operation Aerial Work  
Sector Helicopter  
Damage to aircraft Nil  
Departure point Bulga, New South Wales  
Destination Bulga, New South Wales  
Last update 21 October 2021