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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.

 

 

Preliminary report published: 13 April 2017

The occurrence

On 17 March 2017, a Saab 340B aircraft, registered VH-NRX (NRX) was being operated as RXA768 on a routine passenger flight from Albury, New South Wales (NSW) to Sydney, NSW. On board the aircraft were 16 passengers and 3 crew.

About 55 nautical miles south-west of Sydney airport, the crew noticed uncommanded engine indications and began the necessary checklists. While undertaking the checklist items, the crew experienced minor vibrations from the right engine. These vibrations worsened as the checklist progressed and became visually evident to the First Officer. As a result the crew commenced the engine shutdown procedure. During the engine shutdown procedure, the propeller separated from the aircraft. The crew made a Pan-Pan[1] call to air traffic control, and completed the engine shutdown procedure. The aircraft landed without incident at Sydney airport.

Figure 1: The aircraft, VH-NRX, at Sydney airport after the incident
Figure 1: The aircraft, VH-NRX, at Sydney airport after the incident

Source: Grahame Hutchison

An inspection of the aircraft by the ATSB at Sydney airport identified that the propeller shaft had fractured, leading to the separation of the propeller.

On 21 March 2017, the NSW Police Aviation Support Branch (PolAir) undertook a search operation for the separated propeller. The propeller was located in an area under dense forest about 8NM south-west of Sydney airport.

Figure 2: The propeller that had separated from VH-NRX as found by PolAir about 8NM south-west of Sydney airportFigure 2: The propeller that had separated from VH-NRX as found by PolAir about 8NM south-west of Sydney airport.

Source: ATSB

The propeller was found with the flange section of propeller shaft secured to the propeller assembly and a fracture through the propeller shaft. ATSB subsequently removed the remaining propeller shaft and integral flange section (Figure 4) for examination at its facilities in Canberra.

Propeller shaft examination

The recovered part of the propeller shaft is highlighted in figure 3. The propeller was found properly secured to the forward-facing flange by bolts and the dowel pins pictured. The examination was conducted with representatives present from the Civil Aviation Safety Authority (CASA), SAAB, GE Aviation (engine manufacturer) and Regional Express (REX). Initial observations revealed cracking that appeared to run between the main shaft and the flange region. The part was sectioned in order to expose the crack’s fracture surface.

Figure 3: Propeller gearbox schematic highlighting the recovered section of the propeller shaft

Figure 3: Propeller gearbox schematic highlighting the recovered section of the propeller shaft

Source: GE Aviation, modified by ATSB

The crack was found to be a fatigue fracture that had initiated within the propeller mounting flange, and then transitioned into the shaft section (see figure 4). The crack originated at the bore of a dowel pin near the forward face of the propeller hub flange. The dowel pin bore was corroded in parts (shown in figure 5), and corrosion pitting was found near the fracture. Further work is ongoing to ascertain whether the corrosion or other factors contributed to the fracture initiation.

Figure 4: Section of the propeller shaft showing the fatigue crack originating at the dowel hole and progressing into the shaft itselfFigure 4: Section of the propeller shaft showing the fatigue crack originating at the dowel hole and progressing into the shaft itself

Source: ATSB

This is the first known critical failure of this type initiating within the propeller hub flange of a GE Aviation CT7-9B engine. The same propeller gearbox (PGB) is fitted to multiple variants of the CT7 engine (5A2, 7A1, 9B, 9C, and 9C3) on SAAB 340 and EADS CASA[2] CN-235 aircraft. There is currently no maintenance requirements specified in existing maintenance manuals for routine inspection within the dowel pin bores. Any corrosion or cracking within the bore may go undetected until it progresses to the surface of the flange. Other than a visual inspection of the flange during propeller removal, inspection for surface defects (via magnetic particle inspection or dye penetrant inspection) only occurs when the PGB is disassembled for maintenance at a workshop specifically approved by the engine manufacturer.

Figure 5: Corrosion observed within the bore of the dowel pin hole
Figure 5: Corrosion observed within the bore of the dowel pin hole

Source: ATSB

Safety advisory notice

AO-2017-032-SAN-001:

The ATSB advises that those responsible for the operation and maintenance of SAAB 340 and EADS CASA CN-235 aircraft fitted with the GE Aviation CT7 engine type variants 5A2, 7A1, 9B, 9C, and 9C3 should note the facts presented in this preliminary report with a view to addressing any risks to their own operation.

Proactive safety action taken by GE Aviation

GE Aviation is actively involved in supporting the Australian Transport Safety Bureau in this investigation. The propeller flange and all required hardware has been transported to GE Aviation laboratories in Cincinnati for further metallurgical analysis. GE Aviation is inspecting additional PGBs from the fleet and recommends that all operators follow existing maintenance and inspection procedures. As the investigation progresses GE Aviation will release additional maintenance and inspection recommendations if they become necessary.

Proactive safety action taken by Regional Express

Regional Express has quarantined all propeller gearboxes with propeller shafts of the same series as that installed in VH-NRX.

Further investigation

The investigation is continuing and the ATSB will focus on:

  • maintenance procedures associated with the PGB shaft
  • factors that may have contributed to the fatigue fracture at the propeller mounting flange, possibly including:
    • design and manufacturing of the dowel pins, bores, and overall assembly
    • corrosion protection on the surface of the part
    • opportunities for crack detection.

Should any critical safety issues emerge during the course of the investigation, the ATSB will immediately bring those issues to the attention of the relevant authorities or organisation. This will allow those authorities and organisations to consider safety action to address the safety issues. Details of such safety issues and any safety action in response will be published on the ATSB website at www.atsb.gov.au .

 

______________________

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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  1. A Pan-Pan call is used to declare an urgent situation on-board the aircraft that is not immediately life threatening, but requires assistance from the ground.
  2. In this instance, CASA refers to the aircraft manufacturer EADS CASA and not the Australia Civil Aviation Safety Authority.
 

Updated: 23 March 2017

The ATSB investigation into the in-flight propeller detachment involving SAAB 340 VH-NRX, 19 km SW of Sydney Airport, NSW, on 17 March 2017 is continuing.

With assistance from the NSW Police at Bankstown and NSW Police Air Wing, the investigation team yesterday recovered the propeller assembly in bushland at Revesby in Sydney’s South West. ATSB investigators have also interviewed flight and cabin crew.

The team are now:

  • consulting with the engine and aircraft manufacturers and the aircraft operator
  • reviewing the aircraft’s maintenance requirements and records
  • examining the aircraft’s flight data recorder
  • examining physical components, including the propeller assembly and engine, in consultation with relevant parties.

Updates will be provided as significant information comes to hand.

A preliminary factual report is expected to be publicly released within a month.

 NSW Police prepare to winch the propeller from bushland

 

 

 

Published: 17 March 2017

The Australian Transport Safety Bureau (ATSB) is investigating an incident involving a Saab 340, registration VH-NRX, about 19 km from Sydney on 17 March 2017.

It is reported that the right propeller assembly detached in-flight during the Regional Express (REX) flight from Albury to Sydney, with 16 passengers and three crew on board. The aircraft landed safely at Sydney.

The ATSB is deploying a team of three investigators with expertise in materials failure engineering, recorded flight data analysis, and human factors.

Over the next few days, investigators will examine the aircraft, interview the flight and cabin crew, collect maintenance records and recorded flight data.

Important: The ATSB urges anyone who finds a piece of suspected aircraft debris NOT to handle it. Please call the local police or the ATSB on 1800 020 616.

 

 

Safety issue

AO-2017-032-SI-01 -  

GE Aviation CT7 engine type variants 5A2, 7A1, 9B, 9C, and 9C3

The ATSB advises that those responsible for the operation and maintenance of SAAB 340 and EADS CASA CN-235 aircraft fitted with the GE Aviation CT7 engine type variants 5A2, 7A1, 9B, 9C, and 9C3 should note the facts presented in this preliminary report with a view to addressing any risks to their own operation.

Safety issue details
Issue number:AO-2017-032-SI-01
Who it affects:Those responsible for the operation and maintenance of SAAB 340 and EADS CASA CN-235 aircraft fitted with the GE Aviation CT7 engine type variants 5A2, 7A1, 9B, 9C, and 9C3
Status:Safety action pending

 
General details
Date: 17 March 2017 Investigation status: Active 
Time: 11:49 EsuT Investigation type: Occurrence Investigation 
Location   (show map):Sydney Airport, 19 km SW Occurrence type:Propeller/rotor malfunction 
State: New South Wales Occurrence class: Technical 
Release date: 27 June 2017 Occurrence category: Serious Incident 
Report status: Preliminary Highest injury level: None 
Expected completion: March 2018  
 
Aircraft details
Aircraft manufacturer: Saab Aircraft Co. 
Aircraft model: 340B 
Aircraft registration: VH-NRX 
Serial number: 340B-291 
Operator: Regional Express 
Type of operation: Air Transport Low Capacity 
Sector: Turboprop 
Damage to aircraft: Unknown 
Departure point:Albury, NSW
Destination:Sydney, NSW

Media Release

Statement on Preliminary Report

 
 
 
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Last update 01 August 2017