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225 cleared to fly in UK & Norway

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225 cleared to fly in UK & Norway

Old 9th Nov 2017, 02:15
  #181 (permalink)  
 
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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.
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Old 9th Nov 2017, 23:50
  #182 (permalink)  
 
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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.
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Old 10th Nov 2017, 08:32
  #183 (permalink)  
 
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.....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......
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Old 10th Nov 2017, 11:07
  #184 (permalink)  
 
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Originally Posted by EESDL View Post
.....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......
“Fool me once, shame on you”
“Fool me twice, shame on me”
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Old 10th Nov 2017, 11:58
  #185 (permalink)  
 
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Originally Posted by GrayHorizonsHeli View Post
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.
.
You raise an important point.
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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Old 10th Nov 2017, 12:34
  #186 (permalink)  
 
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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.

Last edited by Fareastdriver; 10th Nov 2017 at 13:31.
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Old 11th Nov 2017, 00:06
  #187 (permalink)  
 
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Originally Posted by Fareastdriver View Post
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.
I hadn't thought of that but yes a good one to note, although I hope to never have to remember it IF I ever get to fly the 332/225 again.

Si

Last edited by bigglesbutler; 11th Nov 2017 at 02:31.
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Old 11th Nov 2017, 01:20
  #188 (permalink)  
 
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Originally Posted by AnFI View Post
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?
AnFI,

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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Old 21st Nov 2017, 16:34
  #189 (permalink)  
 
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Following the recent loss of a 332L in Japan.

https://ad.easa.europa.eu/blob/EASA_..._2017-0232-E_1
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Old 22nd Nov 2017, 13:30
  #190 (permalink)  
 
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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
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Old 23rd Nov 2017, 01:33
  #191 (permalink)  
 
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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
But plenty of chips and MGB changes in 1982 when the type was introduced, 70 MGB changes in the first year of operation.
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Old 23rd Nov 2017, 16:40
  #192 (permalink)  
 
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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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Old 23rd Nov 2017, 16:58
  #193 (permalink)  
 
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Originally Posted by HeliHenri View Post
.
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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The 225 makes for an excellent SAR platform and the SAR variants are exceptional. The military will be able to live quite happily with the current operational restrictions. They have a very different risk profile to the commercial operators where the safety benefits of the new platform to the SAR mission outweigh lingering concerns over the MGB. I would also image they were cut a very decent deal. It is a good place to start rehabilitating the type's reputation. E&P operations are another matter.

Last edited by birmingham; 23rd Nov 2017 at 17:09.
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Old 23rd Nov 2017, 17:18
  #194 (permalink)  
 
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Originally Posted by birmingham View Post
The military will be able to live quite happily with the current operational restrictions.
No military stuff in both cases here.
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Old 24th Nov 2017, 10:12
  #195 (permalink)  
 
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Originally Posted by HeliHenri View Post
No military stuff in both cases here.
I think that is splitting hairs to be honest. My point was that SAR (military, para military, contract or civilian) plus indeed many other military/para military operators will be much less concerned by the ops restrictions than E&P as your own post clearly demonstrates.
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Old 24th Nov 2017, 15:46
  #196 (permalink)  
 
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Saw this video today.

https://m.youtube.com/watch?v=0ZbTN6...ature=youtu.be
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Old 24th Nov 2017, 17:46
  #197 (permalink)  
 
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70 MGB changes in the first year of operation.
Then BHL reduced the Cruise Power Setting and amazing things happened!
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Old 25th Nov 2017, 05:50
  #198 (permalink)  
 
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70 MGB changes in the first year of operation.
Better than 2 rotor separations
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Old 25th Nov 2017, 06:22
  #199 (permalink)  
 
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Then BHL reduced the Cruise Power Setting and amazing things happened!
The point being too much torque is bad for the box. Should have been a lesson for the 225.
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Old 25th Nov 2017, 08:10
  #200 (permalink)  
 
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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.
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