"We'll start writing the ICA supplement after CDR. It's only a couple maintenance tasks."
When I hear this on some STC projects, I sometimes get alarmed. 🙂
While it is ok to release the ICA towards the end, the engineering team should not feel they they finished the design once the "classical" compliance documents are with the CVE, looking at the Instructions for Continued Airworthiness like an appendix that has not been even started yet. Especially if there is no single line or thought documented anywhere about maintainability! 😅
I will use another perspective to explain why the ICA must be drafted from the start, while still using DOA language: this is the operator's perspective, the actual customer. Under 21.A.120B the STC holder must make complete ICA available to all known operators. On the operator's side, that ICA is not an appendix. It is what their CAMO needs to revise the aircraft maintenance programme before, or alongside, the first embodiment. If the ICA arrives patched together as a Frankenstein at the last minute, the STC is approved but the customer can't use it cleanly.
Under this approach this is also when the ICA "develops a habit" of reopening the design. A new inspection task needs access nobody planned for. A proposed interval doesn't fit the operator's or aircraft check package . A life-limited item needs a tracking entry nobody discussed. Each of these is cheaper to solve while the design can still move. The STC projects I've seen deliver smoothly treat the ICA as a design deliverable with its own reviewer, drafted in parallel with the substantiation, not after it. At what stage of your STC projects does the first ICA draft reach someone on the operator's side?