[rotorwrench]

I've read in several descriptions from Ford employees and from historians about release dates for updated parts. Each individual part for the vehicles had to be released for service by engineering after they passed testing. Those parts generally show a production change either in the prefix or the suffix by an alpha letter change.

In my experience with aircraft parts which go through similar engineering changes over time, they use dash numbers to indicate the changes or at least that is the standard I'm accustomed to. The part, as it was originally released, would have no dash number. Some service bulletins refer to them as the part number followed by the term "basic" in parenthesis when there is a directive to change that part for the new dash number part. Ford may or may not have used an abbreviation of this in the service bulletins but I haven't had a chance to go through the bulletins and find any examples so I don't know for any certainty. It's just the only thing that makes sense to my way of thinking. When they obsoleted a part, only the latest revision part number was included in later editions of the parts catalogs. Obsoleted parts were no longer put into the parts catalogs. This practice can lead to confusion when trying to find out what part you need and the number doesn't match the old part. Some times they will indicate "replaces part number such and such" in the description column but not always.

Currently, most helicopter parts catalogs use an "AR" abbreviation in the part quantity for each assembly column and it stands for "as required". They use this a lot where shim washers are required and there is no way to know exactly how many will be necessary. In other books I've also seen the term "As Revised" to indicate a current revision or later future revisions. These items don't really fit with the term we are discussing or at least they wouldn't make as much sense.