I would like to display data from other objects (e.g. maintenance plan) in the current transaction (e.g. change equipment). Is this possible?

Yes; use a "Call" statement to read the data. The function module that you call can be a SAP BAPI, a self-implemented module or the general database access module /guixt/dbselect. For examples see our "Tips, Tricks and Samples" section "Reading the SAP database" .