The access modes can be any relevant combination of (except N which must stand alone):
R read access W write access A append access C common access permitted D directory access N no access permitted
Directory access means that the file may be deleted, or that access mode may be changed.
Norsk Data Document ND–60.050.06 SINTRAN III USERS GUIDE section 3.4.2
Norsk Data Document ND–60.128.03 SINTRAN III REFERENCE MANUAL (printed February 1983), page 1-187