18 Wheeler
As the OP of this topic these comments are directed to you.
You have certainly started a lively discussion here with thread drift that is unbelievable - to the point of some members slagging each other in a rather rude way.
Next time you post you might want to be more specific as it took until page 3 for you to post the real question that you wanted.
Which appears to be:
There was no procedure for dealing with either loss of oil quantity or pressure. Metro 3 type, Garrett TPE-331 engine.
Why?
Had you posted that question in the first page then the answer would have been a lot easier to give you.
The short answer to your question lies in the original certification of the aircraft - in this case SFAR 41. This was a number of exemptions for this type of aircraft to be operated in commercial service without having to be built and certified to "Big" airplane standards.
Ed Swearengen was the original designer and everything about the San Antonio Sewer Pipe was done on the cheap. I would suspect that the flight manual meets the minimum standard for the type but probably not much more.
Back in the day this aircraft was built the authorities still believed in a "Common Sense" approach to flying aircraft - nowadays they not only have to make it "Fool Proof" but have to make it "Damn Fool Proof" as well. Thus newer aircraft have a lot more in the flight manuals.
So the real reason is - because that is how the flight manual was approved in the first place.
Google SFAR 41 and Wiki for the Metro 3 and read.
Regards,
Mx