I noticed during a VOR/DME approach that once I dipped below a thousand feet or so ALT ACQ (Altitude Acquire) appeared on my PFD. What exactly does it mean, and what does it do?

When you get close enough to the altitude in your MCP, the vertical channel mode will change to ALT ACQ from LVL CHG and VS, not sure about VNAV. This means that the FCC signals will try to achieve and hold the selected altitude (and will command either AP or FD to either do so, or show you how to do so)

When you get close enough to the altitude in your MCP, the vertical channel mode will change to ALT ACQ from LVL CHG and VS, not sure about VNAV. This means that the FCC signals will try to achieve and hold the selected altitude (and will command either AP or FD to either do so, or show you how to do so)

 

This is true, also in VNAV. SOP's (at least our says so) states that you select the MDA (rounded up to the nearest 100ft) 2.0NM prior to the FAF. When at least 300ft below the missed approach altitude, you can select missed approach altititude on the MCP (this prevents the ALT ACQ/ALT HOLD). Be aware to turn the altitude up to the missed approach altitude in time and do it fast enough, otherwise the plane has a habit of catching the altitude currently turning in the MCP corresponding with the actual altitude passing (even the real plane). Last but not least, non-precision approaches are fun!

In simple terms it means "Altitude Acquired." Pretty self explanatory. Have fun!