Apologies for the delay in implementing the additional two and three letter exceptions to the search index. I thought they were being added but it is not quite as simple as that.
Currently PPRuNe uses a default 'full text search' from MySql which uses a limit of 4 characters for searches. This can be changed by rebuilding MySql to allow 3, but will increase its work load by quite a bit. Not good.
The other way to solve this is to change the search type. This is done through settings. Doing this will cause the search engine to use the 'good word'/'bad word' lists. However, before we do this, we will need to rebuild the search index but it will take FOREVER due to the large number of posts in the database. We would have to turn off the forums and then hope nothing goes wrong while the search index is being built (Up to a couple of hours).
Once we have finished researching ways to solve this problem we'll implement what is best for PPRuNe and let you know. Sorry for the delays.