Remove uses of .str(), .c_str() and some other methods of SGPath.
Pass SGPath directly where possible, or explicitly convert to the
appropriate 8-bit encoding.
At large search ranges (320 or 640NM range on the 777), the search time can blow up, especially if distant airports are being loaded. Add a time-bounded spatial query, and use it, so performance stays tolerable.
Allow the location of the ND centre to be set from properties instead of always using the acct position.
(I thought I'd supported this option long ago, evidently not)
