What is the significance of the identification number 91-08-07 R1?

• A. This AD was issued in 1981
• B. It indicates the eighth biweekly period (15th or 16th week) of 1991
• C. It indicates the first revision of this AD
• D. This is the seventh AD issued during this period

Answer: (C)

The key idea is that the suffix on an Airworthiness Directive (AD) shows revision status. The digits before the slash indicate the issue year and the AD’s internal sequence, but the important part here is the “R1.” The letter R followed by a number signifies a revision, and the number tells you the revision level. So “R1” means this is the first revision of that AD. When an AD has been revised, you must reference the latest revision to know the current requirements, since revisions can change which aircraft are affected, what inspections or repairs are required, and the timing for compliance. The other interpretations don’t reflect how AD numbering conveys revision status: the year here is 1991, not 1981, and the numbers don’t denote biweekly periods or total AD counts.