The Metro 3 (SA227AC) has no procedure in the AFM for a low oil pressure.
The Metro 23 (SA227DC) does have a procedure in the AFM for a low oil pressure.
i just took the time and looked again at the AFM of the two types i currently operate in our company :
PA42-720 cheyenne III
PA34-200 seneca II
the cheyenne with the PT6A-41 has a procedure like i wrote some time ago for low oil pressure ans splits it :
- when all other parameters normal and engine response normal reduce power as practicable and land soon as possible
-when engine response and/or other parameters abnormal shut down the engine.
the interesting thing : the small seneca with its turbo charged pistons
(TCM TSIO-360)
indeed also has no statement for low oil press in its abnormal checklist.
i must say i never noticed this
but when you read further and go to the engine limits section you
have a minimum oil pressure for operating. i am pretty sure that the metro3 somewhere in its engine limits section has also a minimum oil pressure for operating.
so here you have it indirectly- when you loose oil pressure and go below the minimum operating limit you must not operate the engine and switch over to single engine procedures.
both mentioned planes have NO procedure for low oil quantity inflight, but both
have a minimum allowed quantity for departing when you do your preflight checks .
hope this helps a little.