It is possible the airplane is capable of a coupled approach (e.g., VNAV and LNAV), but the company and/or FAA don't allow it. For example, our 747-400s are not allowed to do VNAV final approaches due to FAA Operations Specifications limits. However, we CAN do coupled approaches down to certain limits (not to landing) using LNAV and Vertical Speed (e.g., VOR, LOC, or NDB/GPS overlay approaches).