WSC is a default spell-checker in FCKeditor 2.6.5. To make SCAYT a default spell-checker in FCKeditor 2.6.5 please follow the instruction below:

1) Open ckconfig.js (…\FCKeditor_2.6.5\fckeditor\fckconfig.js) for edit
2) Change the value of parameter “FCKConfig.SpellChecker” to “SCAYT”

It should look like:

FCKConfig.SpellChecker = 'SCAYT'.