"Finally, it seems astonishing to me that SAC has not yet retrofitted a transmission oil quantity gauge to the S-92. How hard could it be? That's all it would take to eliminate another accident of this type."
FH1100 Pilot,
The oil volume turnover rate in an MRGB like the S-92's is probably about 20 seconds at most. This means the total volume of oil in the lube system circulates from pump-to-sump at least 3 times per minute. If there is a large leak path in the main, single-path circuit (like a dislodged filter housing), then virtually the entire oil supply could easily empty out in less than a minute's time. For such a failure mode, an oil level sensor would not be of much additional benefit.
However, if the leakage was due to something like a shaft seal, and the leakage rate was much less, then an oil level sensor would be of benefit.
If you look at any current aircraft gearbox design (MRGB, AMAD, EMAD, etc.), one thing you'll notice is the absence of external oil lines. The elimination of any potential point of leakage in the lube circuit is something designers strive for. The oil pipes are integrated into the housing casting wherever possible, which makes the casting very expensive, but also greatly improves reliability.
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