Load Lost Due to Misrigged Under Slung Load Control Cable

On 27 April 2017, a Japanese Airbus Helicopters AS350B1JA9743 of Nakanihon Air Service, lost an under slung crop spraying system while in flight at Toubetsu, Teshikaga Town, Kawakami-gun, Hokkaido.  According to the Japan Transport Safety Board (JTSB) final report, released 31 May 2018, the Captain sat in the left seat and a pilot under training was in the right seat and pilot flying.

At around 11:58, as returning to the loading site in order to load the fertilizer to the empty spraying device, the rotorcraft accelerated from the speed at about 25 kt for spraying to the speed at about 60 kt, then turned to right at the altitude at about 50 m.

The under slung load was seen in the helicopter’s rear view mirror to fall away.

Load From Nakanihon Air Service Airbus Helicopters AS350B1 JA9743 (Credit: JTSB)

Load From Nakanihon Air Service Airbus Helicopters AS350B1 JA9743 (Credit: JTSB)

The Hardware

The JSTB explain that:

The Cargo Swing is hung from the bottom of the fuselage by four steel wires, utilizing the rotorcraft structure.

Configuration of Nakanihon Air Service Airbus Helicopters AS350B1 JA9743 Equipped for HESLO / USL External Load Operations (Credit: JTSB)

Configuration of Nakanihon Air Service Airbus Helicopters AS350B1 JA9743 Equipped for HESLO / USL External Load Operations (Credit: JTSB)

The Handle installed in the collective pitch lever is connecting to the [Control] Cable in order to actuate mechanically the Release Unit of the cargo hook device.

The Maintenance Manual requires the Control Cable is routed via clamps at two locations.  On this aircraft the cable was fastened at three locations.  One was a regular routing position but the other two were fastened at non-standard positions. One location used a nylon tie wrap used instead of a clamp.

AS350 External Load Control Cable with Regular Attachment Left and Tie Wraps Found on JA9743 Right (Credit: JSTB)

AS350 External Load Control Cable with Regular Attachment Left and Tie Wraps Found on JA9743 Right (Credit: JSTB)

No maintenance records could be provided that showed when this alternative routing had been done.  This would generate greater bigger friction, would have stopped the Control Cable smoothly following the movement of the Cargo Swing.  This alternative routing also meant the cable was 10cm short at the Release Unit end, resulting in less cable and therefore free movement when attached to the Release Unit.

Control Cable Routing Nakanihon Air Service Airbus Helicopters AS350B1 JA9743 (Credit: JTSB)

Control Cable Routing Nakanihon Air Service Airbus Helicopters AS350B1 JA9743 (Credit: JTSB)

The Control Cable is a Bowden style cable, with a moving inner actuating cable.  On detailed examination the outer protective cables of the Control Cable had broken, exposing the inner moving cable to damage.  However an outer sheath would have prevented this being detected visually.  It is possible that a large movement of the Cargo Swing, would have resulted in the shortened inner cable opening the Release Unit.

JSTB Conclusions

It is highly probable that the serious incident occurred because when the cargo swing was shaken due to the right turn following the acceleration of the rotorcraft to cause the outer cable of the cargo swing broke, the tension was applied to the inner cable, the release unit was activated to open the hook and the spraying device slung was dropped.

Regarding why the outer cable of the cargo swing broke and the tension was applied to the inner cable, it is highly probable that [this was because] the cable routing configuration was different from the regular routing configuration.

JTSB also comment:

Maintaining the regular configuration is important for the safe operation, and it is necessary to reconfirm the method to maintain the appropriate configuration management, like how to maintain the configuration or how to keep the records of the configuration changes

Safety Action

The operator changed all their cables following special training for maintenance personnel on this equipment. They have also reiterated the importance of configuration management to all staff.

No procedural, continuing airworthiness management or assurance changes are mentioned however.

Other Resources HESLO / USL 

Also see our articles:

Other Maintenance Standards and Practice Resources 

Aerossurance worked with the Flight Safety Foundation (FSF) to create a Maintenance Observation Program (MOP) requirement for their contractible BARSOHO offshore helicopter Safety Performance Requirements to help learning about routine maintenance and then to initiate safety improvements:

mop


Aerossurance has extensive air safety, operations, airworthiness, human factors, aviation regulation and safety analysis experience.  For practical aviation advice you can trust, contact us at: enquiries@aerossurance.com