Interesting little bit of information left out in the new AFI regarding the role of the first sergeant.....
AFI 1-1: 1.7.2........The first sergeant works directly for and derives authority from the unit commander, and serves as the commander’s critical link within the unit for all matters concerning its members.
AFI 36-2113 19 Jan 07 (Certified 4 Jan 10): 1.1....The first sergeant works directly for and derive their authority from the unit commander at home station, deployed commander when deployed, and serves as the commander’s critical link within the unit for all matters concerning enlisted members.
The first sergeant is in no way in charge of or has authority over officers. The position of first sergeant is recognized with respect due to the selection process, tradition, and of course, fear of a good ass chewing by your commander after the shirt goes whining to his boss. However, similar to chiefs and other senior enlisted, there are a lot of first sergeants that believe they have authority over officers and fail to adhere to AFI by not recognizing the superior rank of officers when addressing them.
Also of note is that this new regulation references the older regs but does not supersede them. So in my mind, per AFI 34-1201 8.2.2. Juniors shall stand at attention (unless seated at mess or unless circumstances make such action impracticable or inappropriate) when addressed by an officer senior to them