Aux tanks: I personally can't see either the tanks or the sector length having an effect on the filter studs.
Vibration's a funny thing, with sometimes nonlinear effects ... but who would have required an analysis during design of "filter bowl vibe/wear if the torque on the nuts isn't right?" The simple answer to that is "Torque it properly and it won't be an issue."
Oil filtering: 212man, yes perhaps some operators choose to pre-filter their oil. However if that was essential it shuld have been in the Maintnance Manual!
Whose maintenance manual: operator or manufacturer? The decision on how much impact/nuisance/trouble a clogged bowl or popped filter button represents isn't the manufacturer, it's the operator. Pre filtering seems to me an operational decision made based on the number of sorties/missions/trips/legs lost due to such events balanced against typical leg/sortie/mission/trip general factors: over land? Over mountains? Over sea? Twenty minute leg? Two hour leg?
The Manufacturer might not be the best at assessing this for a given operator. Given the variability of oil suppliers, any operator may have
a) best supplier, and no need to filter
b) variable suppliers, and maybe a standing need to filter
Titanium: No matter what reason, gaulling makes titanium a poor material choice and this should have been considered in the FMEA.
Given the cost alone it might have raised an eyebrow ... unless lots of them are used for a variety of applications in numerous production aircraft?
Don't know.
Studs are critical: Two events of oil loss now show that the studs are what FAR29 defines as 'Critical Parts', irrespective of what material they are.
AFAIK they are still not subject to the enhanced critical parts control regieme required by FAR29 for such parts.
It was very instructive (and in hindsight, tooth gritting) to see the TSB analysis of the decision chains after the incident in Australia and before the Cougar mishap.
Blackhawks: Great info guys! A contact in Australian Army tells me that their aircraft have steel bolts (not studs) - highlighting another difference. If the US Army documents are correct in saying the its MGB can operate for 30 minutes without oil then the S-92 is a massive retrograde step and by no means the wonder that some made it oput to be.
I recall some talk (late 90's) that perhaps once S-92 was fielded, its transmission could be backfitted to some of the SH-60 models and allow greater advantage to be taken of the power available from the engines ... acft being torque limited in two eng operation ...