What the item is, where it sits, which tasks call it out
REFERENCE ONLY — not authorized for maintenance, repair or return-to-service. A FIN identifies an item on the drawings of a family of aircraft, not a part fitted to yours: what is actually installed is a question of MSN effectivity and of what the parts catalogue says for that MSN. Two part numbers under one FIN with the same description are not automatically interchangeable. Zones, panels and grid positions here are where the item was recorded, not where it must be.