The nation’s biggest manufacturer and exporter of light aircraft engines has been savaged by the transport safety regulator, which has found that one in 10 Jabiru engines failed or malfunctioned during flight.
A study by the Australian Transport Safety Bureau found engines built by Jabiru, based in Bundaberg in central Queensland, were more than twice as likely to suffer engine failures, malfunctions, or “spluttering” during flight compared to its competitors.
However, the family-run business, which is a significant player in offshore markets, particularly the US and South Africa, has hit back at the report as “extremely biased”, and misrepresenting key details on numerous fronts.
The ATSB report examined all reported cases of engine failures and malfunctions in light aircraft in Australia in the six years to 2014.
In that time, 322 failures or malfunctions were reported to the ATSB, with 130 involving Jabiru engines, around half due to fractured components, in most cases fractures of “engine through bolt”.
Engine through bolts are bolts which hold together the engine’s crank case, which in turn houses the engine’s pistons.
Jabiru, which builds engines for individual sale as well as aircraft, has been aware of the problems for some time and has stopped using the parts in question.
The ATSB compared Jabiru engine incidents against all other makes which suffered incidents in Australia in the period, but Jabiru and three competitors comprised 94 per cent of engine failures or malfunctions, mainly because they were by far the most popular engine types.
The three competitors in terms of both total incidents and incidents per 10,000 hours flown were Austrian-built Rotax engines, engines built by Textron Lycoming of Pennsylvania and those manufactured by Continental Motors, based in Alabama.
Jabiru general manager Susan Woods, daughter of Jabiru founder and owner Rodd Stiff, said the ATSB report was misleading on a number of fronts.
Jabiru’s “light sport aircraft” engines were compared to more expensive competitors used in heavier aircraft and the report failed to take account of the fact Jabiru’s engines were regularly used in experimental or built-at-home planes and were often more susceptible to backyard tinkering by under-experienced hands.
But a key omission was that based on the ATSB’s own data, Jabiru planes were by far the safest in the market segment based on number of fatalities.
“The report was extremely biased and not up to the standard we expect from the ATSB,” Ms Woods told The Australian.
In the 12 years to December there were 1070 registered Jabiru aircraft and 1092 Cessna 172s in Australia and in that time Jabiru aircraft had seen 0.3 fatalities per 100 registered planes compared with 1.8 fatalities for Cessna 172s.
Planes manufactured by Vans RV, a manufacturer of “kit aircraft” which are put together by owners, were the third most popular in Australia in the “light sport” category.
For each 100 registered planes manufactured by Vans RV there were 2.2 fatalities over the past 12 years.
A US study of light sport aircraft accidents by US publication The Aviation Consumer found Jabiru had the lowest fatality rate there (zero between 2005 and 2012) and the second-lowest overall accident rate behind the Cessna 152.
A key reason for the high engine failure rate but low fatality rate was that lighter planes, such as those using Jabiru engines, were easier to manoeuvre with no power.
Ms. Woods said Jabiru was also upset the ATSB had widened its study to include all single-engine aircraft of up to 800kg maximum takeoff weight when light sports aircraft were defined as planes below 600kg.
That change, a deviation from an earlier study by the ATSB, meant Jabiru engines were compared to more expensive and complex engines which were built to more stringent “general aviation” specifications.
“Rotax engines are water cooled and ours are aircooled,” Ms Woods said.
“Aircooled engines require more diligent maintenance, are cheaper to produce but are less complicated and more inviting for people to tinker with”.
Ms. Woods said she had examined each of the 130 Jabiru malfunctions and found a range of issues related to maintenance or pilot error, including fuel line blockages and cases where planes ran out of fuel.
In December 2014, aviation regulator the Civil Aviation Safety Authority, based on its own investigation, placed a string of restrictions on Jabiru aircraft, including restricting them to daytime use, requirements they not fly low over populated areas and that all passengers and trainees pilots sign a statement acknowledging the “accept the risk of engine failure”.
Ms. Woods said Jabiru had been attempting to have CASA lift those restrictions given it had rectified the “engine through bolt” problem, and that CASA had been impressed with Jabiru’s work but it was waiting on the delivery of the current ATSB report before taking any action.
“It’s a bit rough for us at the moment,” Ms Wood said.
Original article can be found here: http://www.theaustralian.com.au
Aviation safety issues and actions
Through-bolt failures in Jabiru engines
Issue number: AR-2013-107-SI-01
Who it affects: Owners and operators of aircraft powered by Jabiru engines
Issue owner: Jabiru Aircraft Pty Ltd
Operation affected: Aviation: General aviation
Background: Investigation Report AR-2013-107
Date: 09 March 2016
Safety issue description
Thicker 7/16 inch diameter through-bolts, fitted to newer Jabiru engines and some retro-fitted engines, have had limited service to date to confirm early indications that they reduce this risk. Retro-fitting engines with thicker through-bolts has only been recommended for aircraft involved in flight training by JSB031 issue 3. Most light aircraft in service with Jabiru engines continue to use 3/8 inch diameter engine through-bolts which, even after upgrades in accordance with Jabiru service bulletins JSB031 issues 1 and 2, remain at an elevated risk of fracturing within the service life of the bolt, leading to an engine failure or malfunction in flight.
Response to safety issue by Jabiru Aircraft Australia
Jabiru Australia has recently completed an engineering study (Through bolt strain gauge test, Jabiru engineering report AVDALSR109-1, 19 November 2015) that has designed and tested a modified 3/8 inch diameter through-bolt which is believed will address the safety issue.
The report states:
….. [the earlier February 2015 Jabiru engineering report AVDALSR105] established that the natural frequency tendencies of the 3/8” through bolt were such that resonance with the engine was likely to occur and this was the probable sources of abnormal (and previously unanticipated) cyclic loads which would cause the bolts to fail.
This report details further work conducted to confirm this hypothesis using an instrumented through bolt installed in a running Jabiru engine. In the course of testing conducted, the nature of loading in the through bolt has been established, vibrational resonance was detected and another aspect of the failure mechanism was uncovered; the previously unanticipated thermal load cycling.
The final tests conducted were on a revised design to the 3/8” through bolt which incorporated aspects to alleviate the effects of thermal expansion and damp resonant vibrations that were found on the standard through bolt.
The revised 3/8” through-bolt was:
designed featuring a more elastic (i.e. less stiff) spring rate and rubber O-rings in the middle to damp resonate transverse vibrations.
Calculations showed significant reduction in preload tension resulting from a given temperature increase for the new design 3/8” through bolt compared to the standard design.
Engine test runs were also conducted. The resonant vibration mode identified for the standard 3/8” through bolt had visibly disappeared with the addition of rubber O-rings. This suggests that the addition of rubber O-rings significantly damps the otherwise damaging resonant vibrations.
ATSB comment in response
The ATSB recognizes that Jabiru Aircraft have conducted a number of in-depth analyses of the mechanism of the through-bolt failures. Additionally, the ATSB acknowledges that Jabiru consider that both the implementation of the 7/16 inch through-bolt, and the development of a revised design 3/8 inch though-bolt, have the potential to address this safety issue across the fleet of all Jabiru engines.
As noted in the internal Jabiru engineering report AVDALSR105-2, most Jabiru-powered aircraft remain at risk of a through-bolt failure. This risk exists because most Jabiru engines in use are still using older configurations of through-bolts. At the time of release of this report, about 20 per cent of engines were manufactured with the new 7/16 inch through-bolt configuration. Some older engines have been retro-fitted to accommodate the thicker through-bolts. However, the recommendation in service bulletin JSB031-3 to upgrade through-bolts to the newest available configuration of through-bolts only pertained to aircraft involved in flight training. As the use of the new 7/16 inch configuration through-bolts is relatively recent, on-going monitoring of the reliability of these through-bolts across the fleet is required.
Up to 80 per cent of the Jabiru engines in service, which have the older 3/8 inch configuration through-bolts, are still at risk. Although Jabiru have designed and tested a revised 3/8 inch through-bolt which incorporates aspects to alleviate the effects of thermal expansion and damp resonant vibrations, it can only address the safety issue once these new bolts are made available to Jabiru engine owners and fitted to relevant aircraft.
Action organization: Jabiru Aircraft Australia
Action number: AR-2013-107-SR-055
Date: 09 March 2016
Action status: Released
The Australian Transport Safety Bureau recommends that Jabiru Aircraft Australia takes further safety action to ensure that all owners of Jabiru engines that have not been manufactured with new configuration 7/16 inch diameter through-bolts, or modified in accordance with Jabiru Service Bulletin JSB031-3 have access to, and are encouraged to upgrade to:
the 7/16 inch diameter through-bolt configuration, or
any other alternative produced to replace the existing 3/8 inch diameter through-bolt configuration (including newly developed through-bolts incorporating aspects to alleviate the effects of thermal expansion and damp resonant vibrations).
Action organization: Civil Aviation Safety Authority
Action number: AR-2013-107-SR-056
Date: 09 March 2016
Action status: Released
The Australian Transport Safety Bureau recommends that the Civil Aviation Safety Authority continue to monitor the through-bolt failure rate of Jabiru engines to satisfy themselves of the reliability of the:
7/16 inch diameter bolts, and
any other alternative produced to replace the existing 3/8 inch diameter through-bolt configuration (including newly developed through-bolts incorporating aspects to alleviate the effects of thermal expansion and damp resonant vibrations)
to determine if these modifications have sufficiently reduced the risk of an engine failure or malfunction in Jabiru-powered aircraft.
Aviation safety issues and actions: https://www.atsb.gov.au