Mods and STCs, proven
Modification and STC status review for managed aircraft before a transaction
Business aircraft accumulate modifications faster than most assets: connectivity systems, avionics upgrades, interior changes, and performance STCs, often installed by different shops under different owners. Ahead of a sale or refinancing, this review verifies that every modification the status report claims is matched by its STC or other approval, the permission to use it for this serial number, installation records, and any required ICA and flight-manual supplements. Aircraft-management teams run it before the data room opens so the modification story is coherent when buyers start comparing paperwork to the airplane. Findings arrive as a per-modification substantiation index with gaps assigned to a recovery owner.
When this review is needed
- The aircraft is going to market and its equipment list reflects upgrades installed across several ownership periods.
- An avionics or connectivity installation was done under a prior owner and the STC permission letter has never been located.
- The flight-manual supplements on board do not obviously match the modification list the status report carries.
- A pre-buy is expected and the management team wants modification findings resolved before the buyer's team raises them.
The problem
Each modification on a managed aircraft was a project someone finished and moved on from. The shop kept its work order, the STC holder issued a permission letter to whoever paid, the supplements went into the flight-manual binder, and the ICA obligations landed on a maintenance program someone else maintains. Years later the status report lists twenty modifications, and the substantiation for them is distributed across shops, prior owners, and binders, with no single file proving any one of them end to end.
What gets reviewed
- The modification status report inventoried against logbook entries, work orders, and the physical configuration record
- Each STC matched to its certificate, the holder's permission for this serial number, and installation data
- Field approvals and minor-change records located for modifications done outside the STC route
- Flight-manual supplements and weight-and-balance amendments checked against the installed modification set
- ICA identified per modification and confirmed incorporated into the maintenance program
- Superseded, removed, or partially embodied modifications reconciled so the list reflects the aircraft as it is
Scope this review
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Send a representative, redacted record set and we will scope the review.
What gets validated
- Every listed modification has an approval document valid for this model and serial number
- STC use permissions exist in a form transferable or re-obtainable for the next owner
- Installation sign-offs cite the approval data actually used, at the revision in effect
- Each modification requiring ICA shows those tasks alive in the current maintenance program
- No flight-manual supplement on board refers to equipment the status report says was removed
Evidence normally required
- The modification and STC status report with the equipment list
- STC certificates, permission letters, field approvals, and minor-change records on file
- Logbooks and work orders covering the installation events
- The flight manual with its supplements and the current weight-and-balance record
- The maintenance-program task list for ICA verification
Common discrepancies
- An STC installed under a prior owner with the permission letter addressed to a defunct entity and no copy on file
- A connectivity system upgraded twice, with supplements for both generations still in the flight manual
- ICA from an interior modification never transferred into the maintenance program after a management change
- A modification listed as embodied whose work order shows it was started, deferred, and never completed
What is at stake
At pre-buy, an unsubstantiated modification stops being an asset and becomes a liability: the buyer cannot confirm the installation was approved for this serial number, cannot verify the ICA are being met, and prices accordingly or demands removal or re-substantiation. Interior and connectivity mods, the very upgrades meant to lift value, are the usual casualties. Sellers then chase decade-old permission letters during the diligence window, when leverage and time are both gone.
Move from findings to resolution
Move from findings to a documented resolution path.
How the work runs
Fix the modification inventory
Reconcile the status report to logbooks and the physical configuration so the list itself is right.
Assemble per-mod files
Collect approval, permission, installation, and ICA evidence for each modification into one substantiation set.
Score and chase
Grade each file, then pursue gaps with STC holders, shops, and prior owners while time remains.
Package for the data room
Deliver the substantiation index and cleaned status report keyed to the evidence.
What the buyer receives
- A substantiation index scoring each modification across approval, permission, installation, and ICA evidence
- A gap list with the recovery route per item: STC holder, installing shop, or prior owner
- A cleaned modification status report ready for the data room
- A flight-manual supplement reconciliation note for the crew and the buyer's reviewers
Who uses the output
- Owner representatives and brokers presenting the aircraft with its upgrades fully defensible
- Maintenance-control staff correcting ICA coverage the review exposed
- The buyer's pre-buy team, ultimately, who receive substantiated modifications instead of open questions
How the work fits into the transaction or program
Modification substantiation slots between the decision to sell and the data-room build, and it interlocks with the logbook and weight-and-balance workstreams that share its source documents. Gaps it finds route to remediation early enough that STC holders and installing shops can still respond within the sale timeline.
Jurisdiction-specific considerations
An FAA-registered managed aircraft leans on 14 CFR Part 21 approvals, STCs and field approvals among them, while a buyer intending EASA registration will re-read the same modification set against Part 21 acceptance and validation requirements under Regulation 748/2012. Modifications approved by only one authority are a predictable friction point in cross-register sales, and the review labels each modification with the regimes its approval actually covers.
Regulatory limits
The review verifies documentation, effectivity, and program incorporation. It does not approve modifications, obtain STC permissions, produce approval data, or determine that any installation conforms or is airworthy. Where substantiation is missing, securing it runs through the STC holder, a design organization, or the authority, none of which this review replaces.
What this review does not cover
- Physical conformity inspection of installed modifications
- Procuring new STC permissions or approval data on the owner's behalf
- Avionics functional testing or software configuration verification
Specific to this review
- STC use permissions are the most commonly missing document in business-aircraft mod files because they were issued to the paying entity at installation, often a holding company or prior owner that no longer exists.
- Two generations of the same system, each with its own supplement, is a recurring finding on connectivity installs; the stale supplement misleads both crews and reviewers.
- ICA loss follows management transitions: the tasks live in the old manager's program and never migrate, leaving an approved modification silently out of compliance with its own instructions.
- A modification the seller cannot substantiate is sometimes worth de-listing before market; an accurate shorter list outperforms a longer one that fails sampling.
- Weight-and-balance amendments are the quiet casualty of serial modifications; each install updated the record in isolation, and the cumulative document often fails to match the final configuration.
Sources
U.S. Government (eCFR). Maintenance recordkeeping content and approval-for-return-to-service requirements, including 43.9, 43.11, and Appendix B.
U.S. Government (eCFR). Type certificates, STCs (Subpart E), TSO authorizations (Subpart O), PMA (Subpart K), and export airworthiness approvals (Subpart L).
Federal Aviation Administration. STC application process, certification basis, and continued airworthiness obligations of an STC holder.
European Union / EASA. EASA design and production certification, STCs, ETSO authorizations, and EASA Form 1 release.
U.S. Government (eCFR). Records an owner or operator must keep, including total time in service, current status of life-limited parts, and AD compliance.
Frequently asked questions
The aircraft flies internationally. Which regime's paperwork matters for the sale?
The registry the buyer intends to use decides. A sale staying on the FAA register turns on Part 21 approvals and permissions; a move to an EASA registry brings validation and acceptance questions for each modification. Because the buyer's plans may not be known early, the review records the approval basis per modification so either path can be answered quickly.
Relevant glossary terms
Related pages
Where this fits
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