225 cleared to fly in UK & Norway

[Concentric]

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?