Shell:
I'm not sure there is any logic in the contention that the quantitative value of 'Extremely Remote' can be 'established' by a manufacturer independently of AC 29.1309. There just cannot be 'n' values of the term - each relevant in its own context. Thus the implication that the value is somehow qualitative is, frankly, laughable.
It would be quite surprising if the failure modes of the lubrication system could be limited to some subset which would leave the oil intact in the gearbox. Reading of the text in FAR 29.927(c)
"Unless such failures are extremely remote,.." would appear to indicate that the test is only required if the FMEA indicates that the failure could occur to a lesser probability than 'Extremely Remote'. The fact that the test was carried out at all appears to indicate that there was a serious situation which had to be managed. Surely testing - if it is called up following an assessment of failure other than Extremely Remote - had to call up the procedure for testing in AC 29.927A!
An extract from the text of the AC appears to be unambiguous and it is not clear how any testing other than with a dry gearbox would suffice:
"The transmission lubricating oil should be drained while the transmission is operating at maximum normal speed and nominal cruise torque (reacted as appropriate at the main mast and tail rotor output quills). A vertical load should be applied at the mast, equal to the gross weight of the rotorcraft at 1g, and the lubricant should be at the maximum temperature limit. Upon illumination of the low oil pressure warning required by § 29.1305, reduce the input torque for Category A rotorcraft to the minimum torque necessary to sustain flight at the maximum gross weight and the most efficient flight conditions. To complete the test, apply an input torque to the transmission for approximately 25 seconds to simulate an autorotation. The last 10 seconds (of the 25 seconds) should be at the torque required for a minimum power landing. A successful demonstration may involve limited damage to the transmission, provided it is determined that the autorotative capabilities of the rotorcraft were not significantly impaired."
Mars