Cobham jet caught fire after company failed to properly repair an engine
Crikey, 2 May 2016
On 29 April 2014 a Cobham Aviation Avro 146 RJ100 caught fire over Perth with 93 people on board at the start of a charter flight to Barrow Island. Cobham’s crew of six handled the emergency perfectly, and the small high winged four-engined jet returned to Perth Airport without injury to any person. But the release of the final report by the ATSB investigation of the incident mightn’t be said to have left Cobham’s reputation untouched.
An engine caught fire and was being fed by fuel under pressure because Cobham for whatever reasons failed to properly repair a fault prior to take off. Had the crew not acted promptly and correctly to the crisis, or the jet not been able to set down on an immediately available airport on its long mostly over water flight, the outcome could have been tragic.
The story about this flight is really two stories.
There is the ATSB report, which is thorough but accessible to lay readers-meaning those of us who could end up being killed in such serious incidents-and there is the diligent manner in which the safety regulator CASA has acted in relation to Cobham, no doubt in close consultation with the Minister responsible for air safety.
(Except that apparently it didn’t because it can’t see any reason why an Australian registered airliner trailing flames over a capital city requires it to do anything.)
This is the core of the ATSB report which can be downloaded in full here with added emphasis.
“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.”
The ATSB’s safety message is that:
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.
Enter, CASA, supposedly the guardians of public safety in the skies, in conjunction with fully informed and proactive ministers.
When a spokesperson for CASA was asked what action the safety regulator was taking in relation to this incident the reply was:
The Australian system does not have prosecutions for organisations. We work under a certificate based system. We also have system based on just culture to ensure open reports such as are made to the ATSB and mistakes rectified.
This statement is completely contrary to statements made by CASA about the legal responsibility for safety outcomes by its previous directors of air safety John McCormick. He even sent letters to the senior managements of the major Australian carriers reminding them that they and their boards were personally liable for the safety outcomes of their operations, regardless of where or by whom maintenance on their aircraft was carried out.
A ‘Just Culture’, in this most recent CASA statement, seems to be shorthand for ‘sod off.’ It is supposed to be about protecting confidences in safety reporting, rather than turning blind eyes on dangerous practices by airlines CASA is supposed to audit for compliance with the rules or procedures that keep passengers safe.
The safety outcome of concern in this Cobham incident is the catching fire of an airliner with 93 people on board over a capital city because of incorrect repair procedures.
What does CASA want before it gets it’s head around this incident. Burned bodies strewn over Perth, and casualties among those on the ground below it?
The safety culture in the US is one of naming, fining and shaming airlines for breaking rules and procedures. Think of it as being what Australia does, or intends to do, for the road haulage and construction industries. But when it comes to airlines, transgressions are buried under fairly floss, making them like banks or financial planners perhaps.
The new Minister Darren Chester is meeting the grass roots aviation industry in Tamworth this Friday, one hopes before the government goes into caretaker mode on the calling of a general election.
It is an important meeting. It is also important for the Minister to note that his predecessors were treated with arrogant contempt by his department in relation to aviation matters and public safety, and that taking visible control of his portfolio and remembering he is a representative of the people, not unaccountable bureaucrats or corporate entities, is a prerequisite for being held in respect.