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Update

Summary

Updated: 27 June 2017

Since the occurrence, the ATSB has been working closely with the engine manufacturer, GE Aviation, in order to establish the factors that led to cracking and fracture of the main propeller shaft from the Regional Express (REX)-operated SAAB 340B aircraft, VH-NRX.

The engine manufacturer’s preliminary metallurgical analysis of the fractured shaft has identified that fatigue cracking in the propeller main shaft originated within a dowel pin bore that was located on the forward face of the propeller flange from the propeller reduction gearbox (PGB). Their analysis indicates that the initiation of fatigue cracking within the hub flange may be associated with a combination of factors that include:

  • the accumulation of significant operational hours for each propeller reduction gearbox
  • the development of pitting corrosion damage within the dowel pin bore and at the front face of the propeller flange
  • progressive wear and subsequent surface damage of the hub flange at stress-critical regions surrounding the dowel pin.

GE Aviation have released two service bulletins (SBs) to help understand the potential fleet risk for fatigue cracking in other CT7 PGB main propeller shafts.

GE Aviation SB 72-0530 ‘Introduction of fleet leader on-wing inspection of PGB shaft’

On 16 May 2017, the engine manufacturer released SB 72-0530 to four main operators of the
CT7-5A2/-5A3/-9B/-9B1/-9B2 series engines. The intent of the service bulletin was to conduct a detailed inspection of the propeller reduction gearbox (PGB) shaft, for the detection of cracking, corrosion, wear damage, and other abnormalities to the propeller hub flange for high-time PGBs. The inspection addressed 12 ‘fleet-leader’ PGBs from each operator and included the following criteria:

  • non-destructive fluorescent penetrant inspection for cracking and corrosion of the PGB hub flange region that surrounded the dowel pins
  • wear measurements of the hub flange
  • detailed visual inspection and documentation of the PGB hub flange physical condition.

The inspection results were to be forwarded to GE Aviation for assessment, with a requested timeframe for completion of one calendar month.

GE Aviation reported to the ATSB that no other instances of cracking were identified through the ‘fleet-leader’ inspection program.

GE Aviation SB 72-0531 ‘Introduction of special on-wing inspection of PGB shaft’

On 22 June 2017, the engine manufacturer released SB 72-0531 to all operators of CT7-5A2/9B/-9B1/-9B2 series engines. The SB applied to all PGBs that had accumulated over 30,000 hours’ time-in-service if the PGB main propeller shaft had not been replaced within 10,000 hours.

The SB is focused on the hub flange region and requires an inspection for cracking, corrosion and wear damage using both detailed visual and non-destructive methods. The following compliance timeframes were recommended for operators to follow:

  • for PGBs that have accumulated over 46,000 hours service, compliance should be within one month, but before accumulating an additional of 150 flight hours
  • for PGBs that have accumulated between 40,000 and 46,000 hours, compliance should be within four months, but before accumulating an additional 500 flight hours
  • for PGBs that have accumulated between 30,000 and 40,000 hours, compliance should be within eight months, but before accumulating an additional 1,000 flight hours.

The ATSB continues to work with GE Aviation and other agencies to determine the factors surrounding this occurrence. The investigation is continuing.

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The information contained in this web update is released in accordance with section 25 of the Transport Safety Investigation Act 2003 and is derived from the initial investigation of the occurrence. Readers are cautioned that new evidence will become available as the investigation progresses that will enhance the ATSB's understanding of the accident as outlined in this web update. As such, no analysis or findings are included in this update.

 

 
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