Most of the avionics I see have a label that says "Mods" and then various numbers checked 1-15.

enter image description here

Image source.

What does this information relate to?


1 Answer 1


This indicates the "mod level" of the hardware in the unit. When a piece of equipment is designed and then certified, it is likely that none of the boxes will be marked.

Then say the product design has a hardware change made to it. Whatever that change consists of is then incorporated into new production units at "mod level" 1. Any units still out in the field won't have this change unless they are reworked to include the modifications. Once the rework is done, the mod plate is then updated to mark the "1" box.

Some installations may require all versions of that equipment to be at a certain mod level in order to meet the certification requirements of that installation.

  • $\begingroup$ Pretty much. I think some equipment may not have all of the mods. Like having mods 1, 2, and 4 if mod 3 wasn't required for whatever reason, but that can be a big headache to manage from a unit configuration standpoint $\endgroup$ Commented Sep 27, 2021 at 19:19
  • 3
    $\begingroup$ Each manufacturer will do it differently as well. Often the mod state is a letter suffix after the Part No or Serial No. $\endgroup$
    – John K
    Commented Sep 27, 2021 at 22:14
  • 4
    $\begingroup$ "Mod" comes from modification. it is also common to refer to different mod levels as revs, short for "revision level" as in rev 1 (as issued), rev 2, rev 3, rev 4 as more revisions are incorporated into the original design. $\endgroup$ Commented Sep 28, 2021 at 4:14

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .