Unfortunately, I have not found a good tool for maintaining a turnpoint
database. John does have conversion routines that can be run on an
existing database, but periodic updates are problematic. And which
format to use for the master data?

If you keep the database in SeeYou .CUP, there is no field for ICAO
code. So if you want to keep the airport identifiers, you are out of
luck. I have asked about extending the CUP format to add an ICAO field,
but TeamCU does not appreciate the difference between an ICAO code and
an abbreviation.

StrePla does support the ICAO field, and will import .CUP, but will not
export .CUP. Also some data is lost in translation. Airport types in
particular. Also StrePla rounds all lengths and elevations to integer
meters, which is annoying if your base data is in feet.

There also is no standard for waypoint codes. CU has just added a bunch
of new waypoint types, but these do not cross reference between
programs.

You also have to deal with all the different length abbreviations in
the different formats. And some formats restrict the number of points,
like the SN10 can only hold 600 or 900 points.

So I have not found a good way either.