225 cleared to fly in UK & Norway
Gearboxes that transmit heavy loads are not new and neither are failures.
Here we have literally hundreds of specimens in all stages of life, from new to near retirement, so lots of specimens for analysis.
It seems pretty straightforward to establish a set of tear down baselines that evaluate the components and then to do some sustained torture testing. The testing obviously has to include appropriate loads. If there is need to create a new test stand and procedure, I'd think the AH team would be well advised to pioneer it.
Presumably the stresses within the gearbox were evaluated during the certification process. If not, one wonders what design and certification criteria are provided.
Hopefully this tragedy will eventually help remove some of the mysteries of gearbox design. That would be fitting monument to the crews and passengers whose lives were lost because of our ignorance.
Here we have literally hundreds of specimens in all stages of life, from new to near retirement, so lots of specimens for analysis.
It seems pretty straightforward to establish a set of tear down baselines that evaluate the components and then to do some sustained torture testing. The testing obviously has to include appropriate loads. If there is need to create a new test stand and procedure, I'd think the AH team would be well advised to pioneer it.
Presumably the stresses within the gearbox were evaluated during the certification process. If not, one wonders what design and certification criteria are provided.
Hopefully this tragedy will eventually help remove some of the mysteries of gearbox design. That would be fitting monument to the crews and passengers whose lives were lost because of our ignorance.
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"Here we have literally hundreds of specimens in all stages of life, from new to near retirement, so lots of specimens for analysis..."
by reducing the OH cycle, they have done this, although tragically late in this case.
I'm curious if the other manufacturers have used this an an opportunity to re-evaluate their own gears too. I'm not convinced that Airbus is the only one at risk here. Are the other makes and models ticking time bombs as well?
whatever went wrong, you can bet Airbus will solve it at some point. they are at least moving in the right direction in my opinion.
can the 225 model survive though? I'm skeptical but remain positive.
by reducing the OH cycle, they have done this, although tragically late in this case.
I'm curious if the other manufacturers have used this an an opportunity to re-evaluate their own gears too. I'm not convinced that Airbus is the only one at risk here. Are the other makes and models ticking time bombs as well?
whatever went wrong, you can bet Airbus will solve it at some point. they are at least moving in the right direction in my opinion.
can the 225 model survive though? I'm skeptical but remain positive.
.....and will anyone believe them when they say they have solved the issue?
Difficult to forget the Airbrush roadshow of 'smoke and mirrors' after the first separation.
They went to great lengths to convince the user that they had it sorted......
Difficult to forget the Airbrush roadshow of 'smoke and mirrors' after the first separation.
They went to great lengths to convince the user that they had it sorted......
Originally Posted by EESDL
.....and will anyone believe them when they say they have solved the issue?
Difficult to forget the Airbrush roadshow of 'smoke and mirrors' after the first separation.
They went to great lengths to convince the user that they had it sorted......
Difficult to forget the Airbrush roadshow of 'smoke and mirrors' after the first separation.
They went to great lengths to convince the user that they had it sorted......
“Fool me twice, shame on me”
Originally Posted by GrayHorizonsHeli
I'm curious if the other manufacturers have used this an an opportunity to re-evaluate their own gears too. I'm not convinced that Airbus is the only one at risk here. Are the other makes and models ticking time bombs as well?
whatever went wrong, you can bet Airbus will solve it at some point. they are at least moving in the right direction in my opinion.
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whatever went wrong, you can bet Airbus will solve it at some point. they are at least moving in the right direction in my opinion.
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Gearboxes are a common concern and every propulsion manufacturer has the scars to show from it. So there is a basis for a more concerted attack on the problem.
In the turbine business, the USAF periodically funds new technology engine prototypes in order to advance the state of the art. Something similar seems warranted for gearboxes, because evidently our understanding of the technology involved is inadequate.
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A common gearbox design of the Puma family is that the annular gear is part of the gearbox housing. This breaks, so does the gearbox, leading to the rotor assembly leaving the aircraft as the stabilising struts are not strong enough to retain it.
All gearboxes need to be redesigned so that there is a failure path which would stop at the annular gear. You will lose your drive but you are still alive and have some control over where the aircraft is going.
Should you lose the main drive in the gearbox in a Puma remember NOT to shut down the engines in the autorotation or you will lose your hydraulics and alternators. The electric pump cannot cope with the rotor control.
All gearboxes need to be redesigned so that there is a failure path which would stop at the annular gear. You will lose your drive but you are still alive and have some control over where the aircraft is going.
Should you lose the main drive in the gearbox in a Puma remember NOT to shut down the engines in the autorotation or you will lose your hydraulics and alternators. The electric pump cannot cope with the rotor control.
Last edited by Fareastdriver; 10th Nov 2017 at 12:31.
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Originally Posted by Fareastdriver
Should you lose the main drive in the gearbox in a Puma remember NOT to shut down the engines in the autorotation or you will lose your hydraulics and alternators. The electric pump cannot cope with the rotor control.
Si
Last edited by bigglesbutler; 11th Nov 2017 at 01:31.
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Originally Posted by AnFI
riff raff
just a hypothetical question
How many gearboxes would you have to run and for how long under what conditions to demonstrate a catestrophic in service failure rate of < 10^-9 per hour?
what is the acceptable catestrophic failure rate for a gearbox? is there one?
just a hypothetical question
How many gearboxes would you have to run and for how long under what conditions to demonstrate a catestrophic in service failure rate of < 10^-9 per hour?
what is the acceptable catestrophic failure rate for a gearbox? is there one?
Sorry for the tardy response.
The answer to your first question is that for single path flight critical systems/components, an example of the FAA threshold for catastrophic failure events is "extremely improbable" as defined in AC 25.1309-1A section 7d. Compliance with this requirement is normally demonstrated entirely by analysis, and the acceptable approach is described in section 8d of the document noted. To demonstrate by test that a complete main gearbox system has a catastrophic failure rate below the "extremely improbable" threshold of 1x10^-9/flight-hour, you would need to test a statistically relevant number of type-confoming gearboxes to their design TBO. And then calculate the failure rate based on the number of catastrophic failures and total accumulated test hours.
One thing you need to consider is the huge number of test hours that might be required to produce a valid result for a very high reliability rate. And each gearbox build would only provide maybe 2000 hrs of test, so you would need to test a very large number of gearboxes. There is some work being done on methods for accelerated life testing, like this example.
Regarding the speed/load conditions used for this type of test procedure they are defined by a "mission profile", which is a representation of the speed/load/time intervals during a typical flight cycle. You can read more about reliability testing in MIL-HDBK-781.
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Confirmation (as was pretty much understood) that this was not a similar incident to those discussed in this thread.
My understanding is that these machines have different MGBs and there have been no MGB incidents on AS 332 C, AS 332 C1, AS 332 L and AS 332 L1 machines that show similarities to the Norwegian 225 incident
My understanding is that these machines have different MGBs and there have been no MGB incidents on AS 332 C, AS 332 C1, AS 332 L and AS 332 L1 machines that show similarities to the Norwegian 225 incident
My understanding is that these machines have different MGBs and there have been no MGB incidents on AS 332 C, AS 332 C1, AS 332 L and AS 332 L1 machines that show similarities to the Norwegian 225 incident
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Back to topic : https://www.verticalmag.com/press-re...5-helicopters/
Second order of the SAR version in few months after the one from the Japan Coast Guard : Japan Coast Guard orders three additional H225 helicopters | Jane's 360
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Back to topic : https://www.verticalmag.com/press-re...5-helicopters/
Second order of the SAR version in few months after the one from the Japan Coast Guard : Japan Coast Guard orders three additional H225 helicopters | Jane's 360
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Originally Posted by HeliHenri
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Back to topic : https://www.verticalmag.com/press-re...5-helicopters/
Second order of the SAR version in few months after the one from the Japan Coast Guard : Japan Coast Guard orders three additional H225 helicopters | Jane's 360
.
Back to topic : https://www.verticalmag.com/press-re...5-helicopters/
Second order of the SAR version in few months after the one from the Japan Coast Guard : Japan Coast Guard orders three additional H225 helicopters | Jane's 360
.
Last edited by birmingham; 23rd Nov 2017 at 16:09.
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Originally Posted by HeliHenri
No military stuff in both cases here.
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Then BHL reduced the Cruise Power Setting and amazing things happened!
But the 225 was the greatest thing since sliced bread according to some at Bristow....far better machine than the very inferior 92 as some told us at great length.
Brand loyalty is fine up to a point....then reality has to be considered.
Did Bristow Engineering not ever raise questions about the possibility of Gearbox issues in the 225 in light of the earlier problems or did they just enjoy the EC/AB Tea and Cookies and sign on the dotted line?
How did that turn out for them?
I mention BHL as they were the Operator with the largest fleet of EC/AB aircraft but the question applies to all of the Operators.
Brand loyalty is fine up to a point....then reality has to be considered.
Did Bristow Engineering not ever raise questions about the possibility of Gearbox issues in the 225 in light of the earlier problems or did they just enjoy the EC/AB Tea and Cookies and sign on the dotted line?
How did that turn out for them?
I mention BHL as they were the Operator with the largest fleet of EC/AB aircraft but the question applies to all of the Operators.
