On my initial course I was told the Trent was certified to run at full thrust with a complete loss of engine oil.If it happened all we needed to do was continue to check oil pressure and temperature and as lond as these did not change we could continue to destination.
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RMC, your original post... NO engine will run for any length of time with a "complete loss of engine oil". Either you've misrepresented what was given in your initial course, or the course is dangerously wrong.
I've not worked the Trent in 20 years, but most engine oil tanks have a couple quarts left when the gauge reads zero - so if it's a slow leak you can keep running for a while with "zero indication", even if the quantity is valid. But the oil pump feeds from the bottom of the oil tank - as soon as the pump starts sucking vapor instead of oil, the oil pressure will start fluctuating and you have a serious problem - all of that oil left in the system is no longer pressurized and won't be doing what it's designed to do.