Aviation safety investigations & reports

Engine failure and forced landing involving Cessna 208B, VH-LNH, 8 km north-west of Solomon Airport, Western Australia, on 16 November 2016

Investigation number:
AO-2016-155
Status: Completed
Investigation completed
Phase: Final report: Dissemination Read more information on this investigation phase

Final Report

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What happened

On the morning of 16 November 2016, a single-engine Cessna 208B aircraft, registered VH-LNH, operated by Aviair Pty Ltd, departed Solomon Airport, Western Australia on a charter flight to Karratha. On-board the aircraft were two flight crew and 11 passengers. Approximately 8 km from the airport, while climbing through an altitude of approximately 4,600 ft, the aircraft sustained an engine failure. The flight crew heard a loud bang and observed smoke billowing from the exhaust.

The flight crew elected to conduct an emergency landing on a nearby dirt road associated with the Solomon mine precinct. The landing was accomplished without injury to the occupants and the aircraft sustained only minor damage.

What the ATSB found

The ATSB found that a compressor turbine blade from the Pratt & Whitney Canada (PWC) PT6A‑114A engine developed fatigue cracking and fractured after approximately 1.8 hours of operation, leading to an in-flight engine failure and forced landing of the aircraft. A repaired compressor turbine vane ring that was fitted to the engine was identified by PWC to contain variations in aerofoil geometry. These variations likely led to an increase in vibratory stresses and the associated development of fatigue cracking and fracture of the compressor turbine blade.

From this and other recent occurrences, the investigation identified that PT6A-114A engines fitted with compressor turbine vane rings that had been repaired in accordance with the United States Federal Aviation Administration (FAA) approved repair scheme STI 72-50-254 had an increased likelihood of CMSX-6 single-crystal compressor turbine blade fracture and subsequent failure of the engine.

The ATSB also found that the flight crew’s handling of the engine failure and subsequent emergency landing reduced the risk of damage to the aircraft and/or injury to the passengers or crew.

What's been done as a result

On 16 March 2017, the holder of the major repair specification for the compressor turbine vane ring, Southwest Turbine Inc. (STI), ceased conducting repairs on CT vane rings for fitment into PWC PT6A-114A engines.

On 29 March 2017, the engine manufacturer, PWC, released Service Instruction Letter (SIL) PT6A-252 to all operators of PT6A-114 and -114A engines. The SIL advised of the heightened risk of CMSX-6 single-crystal compressor turbine blade fatigue fracture when combined with a compressor turbine vane ring that had been repaired using processes that were not approved by PWC.

Pro-active safety action from the aircraft operator, Aviair Pty Ltd, included adopting the recommendations contained in PWC SIL PT6A-252. Their Cessna 208B fleet was reviewed, and any PT6A-114A engines containing compressor turbine vane rings that had been repaired using ‘non-PWC approved processes’, were replaced with CT vane rings produced by PWC.

On 19 August 2019, Transport Canada released airworthiness directive (AD) CF-2019-30 linking the low-time fatigue-fracture of CMSX-6 single-crystal compressor turbine blades and the use of CT vane rings that had been repaired in accordance with repair specification STI 72‑50‑254. The AD required operators to check for, and remove, STI‑repaired CT vane rings from PT6A‑114 and PT6A-34 series engines within a defined period of 9 calendar months, or 250 hours of operation.

The Civil Aviation Safety Authority automatically adopted AD CF-2019-30. This required Australian operators to remove STI-repaired compressor turbine vanes rings fitted to PT6A-114A and PT6A‑34 series engines.

On 17 August 2020, the FAA released a Notice of Proposed Rulemaking advising that they were considering mandating AD CF-2019-030. Public submissions to that process closed on 1 October 2020.

The vibratory effect of repaired CT vane rings on CMSX-6 single-crystal CT blades within PWC PT6A-114A engines was identified as a safety issue by the ATSB. However, due to the significant safety action taken by the directly involved parties since the occurrence, including action from the engine and component manufacturers, as well as the aviation regulatory authorities, the ATSB considers that the risk of CMSX-6 single-crystal CT blade fractures in Australian‑operated PWC PT6A-114A engines has been adequately addressed.

Safety message

This occurrence shows how subtle changes can have a detrimental effect on modern complex turbine engines. In this instance, geometry variations in a repaired compressor turbine vane ring likely led to rapid fatigue cracking and fracture of a compressor turbine blade, and subsequent engine failure.

The incident also reinforces the importance of communication and effective decision-making during an emergency. The crew’s handling of the forced landing minimised the potential for injury or aircraft damage.

VH-LNH Cessna 208B aircraft

Cessna 208B aircraft, VH-LNH .
Source: Jim Woodrow

Source: Jim Woodrow

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The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Sources and submissions

Appendix A: Compressor turbine vane ring measurements

Safety Issue

Go to AO-2016-155-SI-01 -

Compressor turbine blade failure

Pratt & Whitney Canada (PWC) PT6A-114A engines fitted with compressor turbine vane rings that have been repaired in accordance with the United States Federal Aviation Administration‑approved scheme STI 72-50-254 have a significantly increased likelihood of CMSX-6 compressor turbine blade fracture and subsequent failure of the engine compared to those engines fitted with PWC‑manufactured compressor turbine vane rings.

Safety issue details
Issue number: AO-2016-155-SI-01
Status: Open – Safety action pending
General details
Date: 16 November 2016   Investigation status: Completed  
Time: 0751 WST   Investigation level: Systemic - click for an explanation of investigation levels  
Location   (show map): 8 km north-west of Solomon Airport   Investigation phase: Final report: Dissemination  
State: Western Australia   Occurrence type: Engine failure or malfunction  
Release date: 18 December 2020   Occurrence category: Serious Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer Cessna Aircraft Company  
Aircraft model 208B  
Aircraft registration VH-LNH  
Serial number 208B0590  
Operator Aviair Pty Ltd  
Type of operation Charter  
Sector Turboprop  
Damage to aircraft Minor  
Departure point Solomon Airport, Western Australia  
Destination Karratha, Western Australia  
Last update 21 December 2020