Air forces.

Chinook?
 

Surely once the pax lose faith in the aircraft to the extent seen in the N Sea it's effectively finished for the scheduled work? i know the chinook was a very different aircraft to the other aircraft in service at the time, and it didn't have many fans before the sumburgh incident, but aren't there parallels here where pax no longer want to fly in the 225 - despite it continuing service elsewhere and in the military - as did the chinook.

That would be the 725 then and doesn't count in the context of this thread. Military is not engaged in passenger carrying public transport long range high utilisation operations.

That would be the H225M then - do keep up;-)

Ah yes, it would be now I suppose. But a new badge maketh not a new helicopter.

I am very well aware of the differences in operating and maintenance between civil offshore and military operations.
But if the military type would loose a head, I think it would be eagerly included in the Safety statistics by the criticasters of the mother type.
(Not that I am a fan of the type).
Are all losses of the military type been clearified?
I recall the loss of a Spanish one above sea off the Canary Islands?

SLB

Surely the way to resolve this issue is by running the power train under sustained stress.

The 225 gear box has a graceless failure mechanism which was unexpected.
That should be reproducible, given all the clues we have. Running the system full out for 6 months would be ample to hit all the life limits afaik.
What has been learned from such efforts or has nothing such been attempted?

Nope. Almost never.

Unless it crashed, caused life or injury, or the assets itself is new or damn expensive.
"little incident" like inflight flame out, hydraulic leaking, undercarriage collapsed, almost but did not shake off the rotor head due to loose blade pin, window panel falling off, hot start without cranking, APU on when cowling slided back, TR cowling inflight dangling, slice the wheels half while landing with brakes on, glycol injection due to"pressing the wrong button", OEI take-off... unless it is officially reported to OEM, OEM cannot use it in their statistic, at least not the ones published.

Whilst some testing is appropriate and I would hope has been undertaken, I think just running the power train under sustained stress alone might not be the way to replicate the conditions that led to either of the 2 planet gear/bearing premature failures occurring. There are probably many H225 and L2 MGBs that have reached their full service life limit on planet gears without incident.

What you might have to start with is introducing a deliberate surface imperfection, then run the bearing under typical service conditions and examine it at periodical intervals to monitor the growth of any cracks and/or spalling. All that will tell you of course is the rate of growth, not what caused the process to begin by creating the initial imperfection.

This paper describes such a test programme by a well known bearing manufacturer. It also describes the different spalling growth behaviour of ball bearings to roller bearings. The planet gear spherical bearings would approximate to the ball bearing behaviour. Unfortunately the paper only tests a setup where the indentation exceeds the Hertzian width in the rolling direction. It would be interesting to find any testing where the indentation is smaller than say the Hertzian width at typical mid-flight loading.

In my opinion the key area to be investigated is how micro-pits came to be created on the outer raceway. Was it corrosion due to moisture? Was it indentation from fine (or not so fine) metallic particles suspended in the lubricant? Was it a failure of the lubricant to provide or maintain an elastohydrodynamic film between roller and raceway? Was it related to long-term storage rather than operation?

You are correct that the 225 gearbox has a graceless failure mechanism. Part of that is due to the architecture, which Airbus may be unable to change due to certification limitations.

Anyone know of a 225 out there at the moment flying on contract?

Out where? I believe there are at least two in Vietnam that have never stopped.

How many different lubricants are approved for this gearbox?

Perception of "better" is open to interpretation.

From the same manufacturer an example is on some (not all) of the AS350 series you have the option of using a range of mineral and synthetic oils.

All are "approved" yet in this particular case experience dictates that the use of mineral oil will get you much better service life from gearbox components come overhaul.

The difference in the lubricant and their characteristics do have significant effect on all the points that Concentric quotes.

In years past many manufacturers used turbine oils in their main gearboxes. Mostly that has all changed as it worked but not that well in hindsight.

There are much better options available today. More common these days are synthetic industrial or agricultural lubricants and in a lot of cases automatic transmission fluids.

RVDT,

I have been wondering the same since reading your post from 10 years ago.

I do think the lubricant is a very important and possibly overlooked part of this puzzle. The ‘Full Flow Magnetic PLUG’ as Airbus is calling their newfangled magnetic particle ‘detector’ sounds to me like it is in fact more of a Full Flow Magnetic FILTER. These are common enough in terrestrial engineering and manufacturers claim they can remove particles down to sub-micron level.

Despite all the gearbox issues Airbus have had over recent years with the 225 and L2 I am curious as to why they never improved the oil filtration but stuck with a 25 micron traditional filter. As most people on here will be aware, the Sikorsky S-92A has always had 3 micron filtration (while it remained attached, that is) and 3, 5 or 10 micron filtration is now pretty common on industrial transmissions.

Is the introduction by Airbus of what is effectively a fine magnetic filter actually recognition that they needed to purify the oil to a better quality to reduce the risk or rate of micro-pitting, which appears to lie at the root of the bearing failure? It might be embarrassing for them to call it a 'filter' for a couple of reasons including the wording of existing certification that is based on 'detection' of spalled particles. Prevention is always better than cure (or even just detection). Would that have convinced the UK and Norwegian regulators?

The revelation (AIBN report 1.6.9) that 44% of particles in Airbus' spalling test programme were found still in the gearbox must raise questions as to the drainage and internal flow patterns within the casing and/or whether those 44% of particles were finer than 25 microns and were being re-circulated through the filter. If the flow pattern to the lube oil pickup is not ‘full flow’ then the effectiveness of the new ‘FFMP’ or magnetic filter is questionable.

An interesting paragraph (1.18.3) of the AAIB report 2-2011 on G-REDL relates to later findings of particles on another aircraft G-REDN, particularly the 2011 discovery. Quite why, after identifying a particle as 16NCD13 steel, that aircraft was authorised to fly under ‘close monitoring’ for 25 FH then resumed routine flight for a further 87 FH is something that today might be considered unwise. But that isn’t my main point. It is that after finding some particles on the main module MCD, removal of the sump plate found more which were not captured by the MCD. Disassembly of the MGB then recovered "numerous" other metallic particles which had come from a 2nd stage planet gear, and notably silica.

Those findings suggest that not only were the MCDs quite ineffective but that numerous particles were not being flushed down to the sump or picked up by the lube pump (at least not the main lube pump, the one that feeds the 25 micron filter and this new FFMP).

If Airbus is installing this magnetic filter to enhance the existing filter then they ought to look at the internal flow streams within the MGB casing. They previously improved jetting of the vertical shaft bore but the whole gearbox really needs to be looked at for flushing effectiveness, perhaps even off-line flushing on the ground.

They should also remember that silica is not magnetic but it is actually harder than bearing steel. I would not be surprised if the filter pore size is reduced sometime soon as an ‘unrelated’ enhancement.


In other news… whilst everyone’s attention has been on the lifting of the H225 ban by CAA and CAA(N) on 7th July 2017, Airbus and EASA have recalled planet gears of 2 types for the Dauphin family (SA365, AS365 and EC155) according to AD 2017-0116 dated 5th July 2017 citing similar differences in contact stress to the H225 findings. Whatever next?

Regardless of what and how much it was retained in the gearbox, chipping criteria is based on calculation and backed by statistical data. Same goes to damage tolerance on the gearbox. Silica related to 2nd stage gear however, is new to many including me. Can you elaborate more?

Dauphin bearing recall is an AH initiative. If anything is to take away from it, is that they are obviously singling out OEMs. The bearing and gear are totally different from puma. Unlike Puma, dauphin never had the power to hurt the its MGB, It's said in a way that AH might not take my good intention gracefully.

Obviously there should be no silica inside the gearbox. If it does get in there as contamination during gearbox module or mast installation, or during lubricant filling, its hardness might be a factor in starting the creation of micro-pits by causing surface asperities. Is it an Airbus requirement for lubricant to be pre-filtered and piped into the MGB or is it just poured? Is the air breather protected?

The statistical data is:
G-REDL, one chip detected, misinterpreted, catastrophic failure.
G-REDN, several chips detected, one confirmed as 16NCD13, aircraft allowed to fly, numerous more chips detected, planet gear spalled (669FH).
LN-OJF, zero chips detected, catastrophic failure.
What calculations can you perform on that?

If chips have previously been found to be left in the casing and on the sump plate without being detected, how can Airbus be sure the main lube pump sitting higher off the sump will pick them up and deliver them to this FFMP? The standby pump would be more likely to pick them up but that flow will not pass a detector. That is why I think this modification is more about filtering oil that is then delivered to the planetary spray nozzles than detecting macro particles after spalling.

Maybe a stupid question but what is the TBO on the planet gear as in the case of REDN which effectively failed at 669FH, or is it more a case of the whole gear box not an individual component?

Your last paragraph I completely agree with, and brings me back to the 'smoke and mirrors' comment I made earlier, this FFMP sounds a looks good, which in effect I think its :mad: useless

There you completely missed the point and cherry picky what you would like to hear.
And some fact:
REDL did have just one chip.
REDN had numerous chip after "close monitoring" and still flying, nuff said. and I would appreciate if you would quote the conclusion in the report as well.
OJF, until the norwegian can explain why did they drawn up conclusion before they have a clue and been taking hindsight finding like opening christmas present is beyond me.

BTW, rarely seen a gearbox could survive the heavy hover after initial finding. But in the money world, even a rock fell off is acceptable.

Imho I'd be amazed if it returned to the North Sea in any shape or form. The only industry people I've spoken to who think it should and could come back seem to be 99% Airbus personnel or the odd die hard 225 pilot. The loss of confidence in the 225 in the offshore workers is a done thing, it's happened and it ain't coming back. I get that the 225 was a very capable aircraft and better in some ways than the S92, but the confidence has gone. Etched forever in the brain when you think of the 225 is that horrible shot of the windmilling rotor head falling down to the ground. It's finished guys.

I am afraid you have got me there.:rolleyes::confused:

Mee3's message sounds like something Google translate might generate? If however he's a native English speaker, then :eek::eek::eek: