KBT
Sorry,
I did a google search and a search of the NATS web site and totally failed to find the link.
May I suggest that you use the contact form on the NATS web site to ask them, which is what I did originally when I saw it mentioned in an NBAA document. I lost the contact details I had when I changed employers.
If you can wait a fortnight or so I will look on the DVD copy I have at home for a contact and post it here then if there is one.
MM