REX SF34 near Sydney on Mar 17th 2017, propeller detached in flight

Last Update: October 10, 2018 / 13:52:07 GMT/Zulu time

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Incident Facts

Date of incident
Mar 17, 2017

Classification
Incident

Flight number
ZL-768

Aircraft Registration
VH-NRX

Aircraft Type
SAAB 340

ICAO Type Designator
SF34

A REX Regional Express Saab 340B, registration VH-NRX performing flight ZL-768 from Albury,NS to Sydney,NS (Australia) with 16 passengers and 3 crew, was descending through about FL120 towards Sydney cleared to descend to 8000 feet when the crew declared PAN reported they just had had uncommanded engine (CT7) operations, the right hand propeller had sheared off, they still were able to fly with normal handling of the aircraft. Air Traffic Control stopped departures and sent arriving traffic into holds advising a runway inspection was needed, only one runway would remain available and they couldn't estimate when the second runway would become available again due to the landing with one propeller sheared off. A second PAN aircraft (medical emergency), that had earlier been assigned to runway 16R, too, was reassigned runway 16L. The Saab continued for a safe landing on Sydney's runway 16R about 25 minutes later.

Australia's TSB reported the occurrence was rated a serious incident. Three investigators with expertise in materials failure engineering have been dispatched on site. The ATSB urged: "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."

Sweden's Statens Haverikommission (SHK) assigned an accredited representative to assist the investigation by the ATSB.

On Mar 21st 2017 the ATSB reported the separated propeller assembly weighing about 100kg/220lbs was found by a police helicopter at the Georges River National Park about 8nm west of Sydney Airport.

The airline grounded 5 more Saab 340s in order to secure propeller gear boxes and shafts of the same production series for detailed examination.

On Apr 13th 2017 the ATSB reported that the recovered propeller was still securely fastened with the bolts and dowel pins to the forward facing flange of the propeller shaft. Initial inspection showed cracks that appeared to run between the propeller shaft and the flange. Further examination revealed the crack was a fatigue crack that started within the propeller mounting flange and then propagated into the shaft section. The crack initiated at a bore of a dowel pin near the forward face of the flange. The dowel pin bore was corroded in parts and corrosion pitting was found near the fracture. The ATSB stated that this was the first critical failure of this type originating within the propeller flange. REX have quarantained all propeller gear boxes with the same flange as VH-NRX. Further examinations are under way at the engine manufacturer.

On Jun 27th 2017 the ATSB provided an update stating:

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.

The ATSB continued the first of the two service bulletins, SB 72-0530 released on May 16th 2017, which intended to conduct detail inspections of the PGB shaft for detection of cracking, corrosion, wear damage and other anomalies. The second service bulletin, SB 72-0531 released on Jun 22nd 2017 and applicable to all PGBs with more than 30,000 hours in service if the main propeller shaft had not been replaced within the last 10,000 hours in service, requires inspections of the hub flange region for cracking, corrosion and wear damage employing visual non-destructive methods.

A Saab 340A, registration N146CA, had lost the right hand propeller on Nov 21st 1991 following engine (CT7) vibrations. The NTSB concluded in their final report then: "A FATIGUE FRACTURE ON THE PROPELLER SHAFT, THAT ORIGINATED AT A SUBSURFACE SLAG INCLUSION, WHICH REMAINED IN THE MATERIAL USED TO MANUFACTURE THE SHAFT."

On Oct 10th 2018 the ATSB released their final report concluding the probable causes of the serious incident were:

Contributing factors

- The propeller shaft failed as a result of a fatigue crack that had initiated at the dowel pin hole and propagated through the shaft until it could no longer transmit the required loads.

- The engine manufacturer did not have specific inspection procedures in the maintenance documents of the propeller shaft to detect a fatigue crack originating from the dowel pin hole. [Safety Issue]

Other safety factors

- The form used by Regional Express during a propeller removal and installation, HM-26 Revision 5, included the task to inspect the propeller gearbox, but did not provide for recording of inspection findings as defined within documented procedures. Consequently, this did not provide for the best opportunity to ensure potential defects were identified, recorded and monitored.

Other findings

- The flight crew used checklist management and crew resource management effectively. These factors combined to contribute to a positive outcome for the aircraft.

- The ATSB and the engine manufacturer, General Electric, were unable to determine conclusively the reason for the fatigue crack initiation and propagation.

The ATSB praised the crew in their analysis:

The in-flight loss of propeller involving Saab 340B VH-NRX at 10 NM south-west of Sydney, New South Wales (NSW), on 17 March 2017, was the result of the fracture of the propeller shaft on the right engine propeller reduction gearbox (PGB). The shaft fracture led to the separation of the propeller from the aircraft. The flight crew performed an uneventful single-engine landing at Sydney Airport. The crew showed a high level of professionalism in their response to the engine failure and loss of a propeller. The crew demonstrated high levels of communication and coordination, and promptly applied checklists and procedures.
Aircraft Registration Data
Registration mark
VH-NRX
Country of Registration
Australia
Date of Registration
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Airworthyness Category
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TCDS Ident. No.
Manufacturer
S.A.A.B. AIRCRAFT CO
Aircraft Model / Type
340B
ICAO Aircraft Type
SF34
Year of Manufacture
Serial Number
Maximum Take off Mass (MTOM) [kg]
Engine Count
Engine
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Main Owner
H i jAipkmlplhkbilpfblqcmmfdicegjpjlm AdgjpfcAAcmbjAlmmqm jbglieqqdqmejlcgpAmfklcqknh Subscribe to unlock
Main Operator
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Incident Facts

Date of incident
Mar 17, 2017

Classification
Incident

Flight number
ZL-768

Aircraft Registration
VH-NRX

Aircraft Type
SAAB 340

ICAO Type Designator
SF34

This article is published under license from Avherald.com. © of text by Avherald.com.
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