What certification basis are you doing these inspection/repairs under ? Is this part 23 , part 25, DOD ? More information will get you a better answer. "On condition", can range from a daily inspection/ Pre flight to 100 hour, to Annual inspection. If at annual it is in a " Pass " condition, then it is good for one more year. Is this what you really want?
B.E.

You are judged not by what you know, but by what you can do.

@Berkshire

The authority asked us to develop a general (Part 23, 25, 27 & 29) procedure on how to develop the inspection limits and intervals for modification/repair (minor).
For an example: installation of an antenna on the fuselage (part 27) of the rotorcraft. We put 'on condition' for the visual inspection of the antenna. Or we might put perform visual inspection of the installation as per AMM which the manual stated to perform it annually (example). But they refused to accept this saying that the Para on the AMM is for without the modification.

Another example:

Part 25 Appendix H
(a) The Instructions for Continued Airworthiness must contain a section titled Airworthiness Limitations that is segregated and clearly distinguishable from the rest of the document. This section must set forth--
(1) [Each mandatory modification time, replacement time, structural inspection interval, and related structural inspection procedure approved under § 25.571.

For minor modification usually it does not requires to comply with FAR 25.571. Does this means that for minor modification it is not necessary to have detail inspection interval, as 'On Condition' is sufficient?

for you antenna installation, did you create a fuselage penetration ? add an external doubler ?? or maybe you installed an antenna on existing OEM provisions ???

If you've done a DTA of your installation and shown no inspections are required then why do you need a section in the ICA ? ACtually it sort of makes sense, to give visibility to the fact that analysis was completed and no inspections are required (rather than to have people wonder).

another day in paradise, or is paradise one day closer ?

its.me.lah [whateverthatmeans]...

The General FAA/DOD guidance to ensure that structural mods allow for ease of interior and exterior inspections... that will ensure incipient damage [cracking, loose/missing fasteners, distortion, etc] is readily apparent is a wise-way-to design the mod.

Also...

One thing I discovered about mods like this... especially involving small electronic stuff that may be grounded-to/poking-thru the fuselage skin... is poor attention to corrosion-protective finishes that eventually cause structural corrosion... or worse... electrical grounding-point corrosion. A well designed structural mod [repair, retrofit, replacement, etc] with poor integration of corrosion protection is why many structures problems begin... or become aggravated.

Regards, Wil Taylor

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