Aviation safety investigations & reports

Main rotor blade crack and precautionary landing involving Robinson R22 Beta, VH-HPH, 12 km south-west of Labelle Downs Station, Northern Territory, on 16 December 2016

Investigation number:
AO-2016-174
Status: Completed
Investigation completed
Phase: Final report: Dissemination Read more information on this investigation phase

Final Report

Download final report
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What happened

On the afternoon of 16 December 2016, the pilot of a Robinson Helicopter Company (Robinson) R22 Beta, registered VH-HPH and operated by North Australian Helicopters, was conducting mustering operations at Labelle Downs Station in the Northern Territory. About 12 km south‑west of the station property, the pilot was alerted to the onset of vibrations and conducted a precautionary landing. The landing was accomplished without incident. A subsequent ground inspection revealed the presence of a large crack through one of the main rotor blades.

What the ATSB found

Laboratory analysis of both main rotor blades (part number A016‑6) at the ATSB’s facilities in Canberra identified that a significant fatigue crack had propagated almost entirely through the blade chord at rotor station 61.3, which led to instability and vibrations of the aerofoil structure during the occurrence flight. The analysis identified that the fatigue crack initiated at the trailing edge bond line, and propagated through both the upper and lower blade skins until terminating at the leading edge D-spar.

It was possible that a number of variables influenced the initiation of the blade cracking, including the component’s design, manufacture and operation. The ATSB was unable to determine conclusively which factors, either individually or in combination, contributed to the crack initiation.

A search of aviation defect databases found no other examples of fatigue cracking in R22 A016-6 main rotor blades. The helicopter manufacturer reported to the ATSB that they were only aware of one other instance of A016-6 blade cracking.

What's been done as a result

Following the occurrence, on 22 December 2016, Robinson issued a Safety Alert ‘A016-6 Main Rotor Blade Crack’. It detailed the crack location, and recommended particular attention from pilots and maintainers when visually examining the trailing edges of blades during the daily or pre-flight inspection.

Robinson also redesigned the A016-6 main rotor blades to allow for a longer trailing edge doubler in order to eliminate potential stress gradients from stiffness variations along the trailing edge. A prototype A016-6 blade containing the extended doubler was test flown in January 2017, before entering production as Revision AV blades in February 2017.

The Australian Civil Aviation Safety Authority issued an Airworthiness Bulletin (AWB) 62-006 ‘R22 Main Rotor Blade Cracking’ to alert R22 operators and maintainers of the occurrence. The AWB was released on 23 December 2016 and highlighted the need for particular vigilance during the daily or pre-flight checks of the main rotors, and for pilots to be alert to sudden and increased vibrations.

Finally, North Australian Helicopters reinforced with staff the manufacturer’s recommended procedures for conducting the daily and pre-flight inspection of the main rotor blades and the need to land immediately should unusual vibrations increase or develop during flight.

Safety message

The ATSB reminds helicopter pilots, operators and maintainers that fatigue cracking can occur on critical flight components. Particular vigilance should be applied during the daily or pre-flight inspections as they represent an important opportunity to detect cracking. As recommended by Robinson in their Safety Alert, ‘A016-6 Main Rotor Blade Crack’, any form of damage such as paint blistering, denting, and corrosion to the main rotor blade surfaces is cause for further investigation. Pilots are also reminded to heed Robinson’s advice contained in Safety Notice 39 ‘Unusual vibration can indicate a main rotor blade crack.

A catastrophic rotor blade fatigue failure can be averted if pilots and mechanics are alert to early indications of a fatigue crack.

If main rotor vibration rapidly increases or becomes severe during flight, make an immediate precautionary landing. Do not attempt to continue flight to a convenient destination.

Robinson R22 Beta, VH-HPH

Robinson R22 Beta, VH-HPH.
Source: North Australian Helicopters

Source: North Australian Helicopters

Download final report
[Download  PDF: 2.39MB]
 
 
 

The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Appendix A: R22 safety alert

Appendix B: Airworthiness bulletin

Sources and submissions

General details
Date: 16 December 2016   Investigation status: Completed  
  Investigation level: Defined - click for an explanation of investigation levels  
Location   (show map): 12 km south-west of Labelle Downs Station   Investigation phase: Final report: Dissemination  
State: Northern Territory   Occurrence type: Propeller/rotor malfunction  
Release date: 06 May 2020   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer Robinson Helicopter Co  
Aircraft model R22 Beta  
Aircraft registration VH-HPH  
Serial number 3988  
Operator North Australian Helicopters  
Type of operation Aerial Work  
Sector Helicopter  
Damage to aircraft Minor  
Departure point Labelle Downs (ALA)  
Last update 07 May 2020