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What happened

On 29 April 2014 an AVRO 146-RJ100 aircraft, registered VH-NJI and operated by Cobham Aviation Services Australia (Cobham), was on a charter flight to Barrow Island Airport from Perth Airport, Western Australia. The aircraft sustained a mechanical failure of the No. 2 engine shortly after take-off that resulted in an in-flight fuel-fed engine fire.

The flight crew extinguished the engine fire by shutting down the No. 2 engine and activating the fire suppression system. The aircraft was flown back to Perth Airport, having sustained significant damage to the No. 2 engine and cowling. There were no injuries.

What the ATSB found

The Honeywell International Inc (Honeywell) LF507-1F (LF507) engine has four combustion liner locating pin welded bosses (welded boss) in the combustor turbine module (CTM) combustor housing (housing). The ATSB found that the welded boss located at the 2 o’clock position had cracked and fractured adjacent to the weld as a result of fatigue. The boss separated from the housing, allowing high-pressure combusting fuel to escape radially through the CTM housing, burning through the engine cowling.

The ATSB also found that localised grinding of the inner and outer surfaces of the CTM housing, adjacent to the welded boss, had reduced its wall thickness from 0.050 to 0.035 inches. The reduced wall thickness increased local stresses and hence the likelihood of crack formation. The crack accelerated at an unpredictable rate until penetrating the full thickness of the housing. It is likely that the grinding was associated with a weld repair conducted during a CTM heavy maintenance visit. The grinding repair was not an acceptable repair to Honeywell for returning the component to the original design strength.

Finally, the ATSB found that the normal scheduled visual inspection of the housing, which was designed to find cracks before they developed into a fracture, was ineffective in this case. This was because the reduced wall thickness invalidated the original crack growth rate predictions.

What's been done as a result

In response to this occurrence Cobham proactively inspected all of their LF507 engines, focusing on the welded bosses. Of those engines, one spare engine had grinding at one of the welded bosses, similar to the occurrence engine, and was withdrawn from the availability pool. Although no cracking was found at the combustion liner location pin welded bosses, Cobham did find seven cracks at the location of the ignition bosses that had not been previously identified. These cracks were managed in accordance with the Honeywell maintenance manual.

Honeywell also instigated several actions in response to this occurrence. These included amendment of the LF507 engine maintenance and overhaul manuals to address crack limits and weld repair specifications, and the issue of a Service Bulletin to alert operators of possible welded boss cracking.

Safety message

This occurrence highlights the importance of repairing aircraft components in accordance with the manufacturer’s specifications and ensuring that the repair meets the design intent of the manufacturer.

VH-NJI in-flight fire damage

VH-NJI in-flight fire damage
Source: Jason Grimmett

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The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Sources and submissions

 
 
 

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Published: 5 December 2014

The occurrence

On 29 April 2014 an AVRO 146-RJ100 aircraft, registered VH-NJI and operated by Cobham Aviation Services Australia (Cobham) on a on a charter flight from Perth Airport to Barrow Island, Western Australia, sustained an in-flight fuel-fed fire in the No. 2 engine during or shortly after take‑off (Figure 1). The flight crew shut the engine down and activated the fire suppression system before returning to Perth for landing.

Figure 1: No. 2 engine showing fire damage (looking forward)

No 2 Engine Fire Damage
Source: Cobham (edited by the ATSB)

Initial examination

Engine damage

Initial examination by the Australian Transport Safety Bureau (ATSB) found that a portion of the Honeywell ALF‑507-1F engine’s combustor housing fractured at about the two o’clock position, looking forward, and was ejected from the engine. The fracture occurred at a welded boss that facilitated one of four combustion liner locators per engine. A portion of the combustion liner adjacent to the damaged area of the combustor housing also failed (Figure 2).

Figure 2: No. 2 engine showing combustor housing and combustion liner (looking forward)

No. 2 engine showing combustor housing and combustion liner
Source: Cobham (edited by the ATSB)

The breach of the combustion liner and engine combustor housing created a radial escape path for the fuel–fed, high pressure combusting gases. These gases quickly burnt through the engine cowling in that location.

Engine and other recorded information and documentation

Recording devices that captured the No. 2 engine parameters prior to and during the occurrence were retained for further analysis. All of the operator’s maintenance documentation related to the No. 2 engine, including its overhaul and engine trend condition monitoring records, have been secured for further analysis.

In addition, the cockpit voice recordings have been reviewed and the flight crew interviewed. At this stage, no operational factors have been identified that may have contributed to the occurrence.

Failed components

The ejected section of the engine combustor housing was recovered from inside the No. 2 engine cowling for technical examination at the ATSB’s facilities in Canberra, Australian Capital Territory.

The engine was removed from the aircraft and sent to an approved maintenance repair and overhaul facility in the United Kingdom (UK) for technical examination under the supervision of the UK Air Accidents Investigation Branch. This disassembly and subsequent examination of the engine’s ‘hot section’ found that, in addition to the fractured welded boss in the combustor housing, there were three other areas of damage on the housing. The combustion liner was also found to have failed in several locations. Further analysis is planned to establish if the damage to the hot section was a result of the failure, or contributed to the failure.

A number of components from the engine hot section, together with the ejected section of the engine combustor housing have been shipped to the engine manufacturer’s facilities in the United States for further analysis under the supervision of the National Transportation Safety Board. This will include destructive testing of a number of components.

The forward, section of the engine has been quarantined in the UK for possible further analysis.

Safety action

Cobham Aviation Services Australia

At this stage of its investigation, the ATSB has not identified any organisational or systemic issues that might adversely affect the future safety of aviation operations. However, Cobham has advised that it has inspected all combustor housings in their ALF‑507-1F engine fleet in the area of the combustion liner locating pin boss welds.

No other cracks in the welds in this area were identified in any of the engines.

Ongoing investigation

The investigation is continuing and will include examination of the:

  • recorded data
  • No. 2 engine maintenance documentation
  • No. 2 engine trend condition monitoring records
  • history of the ALF‑507-1F engine for previous similar occurrences
  • recovered hot end components and ejected section of the combustor housing.

_____________________________

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.

 
General details
Date: 29 April 2014 Investigation status: Completed 
Time: 10:45 WST Investigation type: Occurrence Investigation 
Location   (show map):Perth Airport Occurrence type:Engine failure or malfunction 
State: Western Australia Occurrence class: Technical 
Release date: 02 May 2016 Occurrence category: Serious Incident 
Report status: Final Highest injury level: None 
 
Aircraft details
Aircraft manufacturer: British Aerospace PLC 
Aircraft model: AVRO 146-RJ100 
Aircraft registration: VH-NJI 
Serial number: E3265 
Operator: National Jet Express 
Type of operation: Air Transport High Capacity 
Sector: Jet 
Damage to aircraft: Substantial 
Departure point:Perth, WA
Destination:Barrow Island, WA
 
 
 
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Last update 02 May 2016