2- Databases: what is the most used/common third-party aircraft registration information currently available (for spotters, etc)?
Airnav
Another long one, I am sorry. My beef is more about clearing out the aircraft that are departed and the glaring errors which stick out like a sore thumb to us users that access Database explorer daily. Sort the DB3 by field AC and you will find aircraft of many defunct airlines like Pan Am, TWA, ATA, Zoom, EOS, Maxjet, Braniff.
I use
http://www.airlinerlist.com/ They have downloadable spreadsheets which are kept very up to date. It covers commercial and bizjet types aircraft types down to Otter/Cessna 208 size.
To edit, I filter my database explorer AT field for one old aircraft type, then find the registrations one-by-one in the appropriate airlinerlist spreadsheet to ascertain if it is still current or not. Unfortunately it is a manual process which is why I recommended a vacation job would be the best way to do it.
For example just now I sorted the C500 list. I started with 212 DB3 entries. Comparing each one to the production list, I was able to identify and remove 58 airframes that were either scrapped or reregistered (around 1/4). In all it took me around 20 minutes to review all entires for that type.
I also found N501GB. It is a current C500 Citation C/N500-0231 registered in 2002. Your released NavdataDB3 database given to users ascribes it to a Lockheed Tristar of Nordic European Airways deregistered 13 years ago. It is these obvious items that could be seen and cleared up by one of your developers just by scanning through the list. It appears to us users that you trusted the computers to populate the NavdataDB3 and have never cast a human eye on it to find even the most glaring errors.
Other examples of what can easily be cut away. Since 2001 the major US carriers have retired 727s (united, american), B742 (northwest), A306 (american), B737s (united), JS31 (every major feeder airline) etc. Simple sorts by airline name and aircraft type could remove hundreds of these airframes that are still in the DB3. You could use the fleet lists at
http://www.ch-aviation.ch/aircraft.php to confirm which full fleets have been put to grass.
I am not suggesting that you need to fully manually review all 82,000, just pass a manual eye over airline names for defunct airlines and the older fleets like 707s, 727s, Tristars, DC9s, 737-200s, sabreliners, jetstars etc. Through this manual review & deletion process, solely using the delete button on Database explorer, I have got my personal Navdata file under 50,000 entries with less than circa 2 weeks work.