TSO navigation
TSO compliance evidence support for navigation equipment
This support maps a navigation equipment item's evidence to the Technical Standard Order it is approved against, with attention to the functional class and accuracy the standard defines. It is run by the navigation supplier assembling a TSO authorization application or answering a finding. The work checks coverage of the invoked minimum performance standard, whether the functional class claimed is supported by the accuracy and integrity evidence, how the DO-178C software level backs the position functions, and the article-versus-installation boundary. You get a standards map to the TSO and its invoked standards, a ranked evidence gap list, and a closure sequence.
When this review is needed
- A TSO authorization application for a navigation unit is being assembled and its evidence needs mapping to the standard.
- An authority questioned whether the functional class claimed is supported by the accuracy and integrity evidence.
- The unit claims a capability the accuracy data does not yet substantiate at the level the class requires.
- Reviewers are folding installation-dependent navigation performance into the TSO article evidence.
The problem
Navigation TSOs are built around functional classes, and the class a unit claims is a promise about accuracy, integrity, and availability that the evidence has to keep clause by clause. The trap is claiming the higher class the marketing wants while the test data supports the one below, or resting an accuracy figure on a bench result that the software level does not underwrite. Because navigation performance shifts with the installation and the signal environment, the article evidence and the installed performance blur together, and the class claim floats above the data that should anchor it.
What gets reviewed
- Coverage of the minimum performance standard the navigation TSO invokes
- Functional class claimed against the accuracy, integrity, and availability evidence
- DO-178C software level supporting the position and integrity functions
- DO-160G environmental qualification matched to the TSO categories
- The boundary between article performance and installation-dependent performance
- Marking and data requirements the TSO article carries
What gets validated
- The functional class claimed is supported by accuracy and integrity evidence at the required level
- Each clause of the invoked performance standard maps to specific test or analysis evidence
- The software level underwrites the integrity the claimed class depends on
- DO-160G categories cover the intended installation environment
- Installation-dependent performance is kept out of the article evidence and flagged separately
Evidence normally required
- The applicable navigation TSO and its invoked minimum performance standard
- Accuracy, integrity, and availability test evidence for the claimed functional class
- DO-178C plans and software level records for the position and integrity functions
- DO-160G qualification test reports for the article
- The article's marking and data plates as designed
Common discrepancies
- A functional class claimed above what the accuracy and integrity evidence supports
- An integrity function whose software level is below what the claimed class requires
- Installation-dependent navigation performance substantiated inside the article evidence
- A clause of the performance standard with no matching test evidence
What is at stake
A navigation unit whose functional class outruns its evidence draws a finding that the claimed capability is not substantiated, and closing it means either downgrading the class or generating the accuracy and integrity data the higher class demands. If installation-dependent performance is carried inside the article evidence, the authorization scope blurs and the supplier absorbs substantiation the installer owns, which surfaces late and costs the schedule.
Move from findings to resolution
Identify gaps against the means of compliance.
How the work runs
Anchor the class claim
Check that the claimed functional class is supported by accuracy, integrity, and availability evidence at the required level.
Trace the integrity software
Confirm the software level underwrites the integrity the claimed class depends on.
Cover the standard
Map each clause of the invoked performance standard to specific test or analysis evidence.
Draw the boundary
Separate installation-dependent performance from the article evidence and sequence the remaining gaps.
What the buyer receives
- A standards map to the navigation TSO and its invoked performance standard
- A ranked evidence gap list tied to the functional class claim
- A closure sequence identifying whether to downgrade the class or generate more evidence
Who uses the output
- Certification leads assembling the navigation TSO application
- Test and systems engineers reconciling the class claim with the accuracy data
- Compliance managers responding to a TSO finding on the navigation article
How the work fits into the transaction or program
This review works at the article level beneath the installation approval a type change or STC will carry. It confirms the navigation unit's functional class is anchored in its evidence and its TSO cleanly covered, so the authorization stands on its own and installed-performance questions are handled where they belong rather than inside the article package.
Start with a single asset
Confirm requirements trace through verification.
Jurisdiction-specific considerations
The FAA TSO and the EASA ETSO for navigation equipment often invoke the same performance standard and functional classes, but their treatment of integrity substantiation and deviation can diverge. The map notes where evidence sufficient for one authorization needs supplement for the other so a dual navigation approval does not stall on the integrity argument.
Regulatory limits
This work maps and checks the article evidence against the navigation TSO and its invoked standards. It does not grant an authorization, set the functional class on the authority's behalf, or make an airworthiness determination on the installed unit. Those decisions rest with the applicant and the certifying authority.
What this review does not cover
- Running the accuracy, integrity, or DO-160G testing itself
- Substantiating installed navigation performance on a specific aircraft
- Any determination that the navigation article is airworthy or approvable
Specific to this review
- A navigation functional class is a claim about accuracy, integrity, and availability, and the class most often outruns the evidence that should anchor it.
- The integrity function is where the software level matters most; a class that needs high integrity cannot rest on software assured below it.
- Navigation performance shifts with installation and signal environment, so the article-versus-installation boundary is easier to blur here than on most equipment types.
Sources
U.S. Government (eCFR). Type certificates, STCs (Subpart E), TSO authorizations (Subpart O), PMA (Subpart K), and export airworthiness approvals (Subpart L).
RTCA. Environmental qualification test categories and procedures referenced by TSO and equipment qualification.
RTCA. Objectives and lifecycle data for airborne software assurance, by design assurance level (DAL A-E).
Frequently asked questions
What happens if the functional class we claimed isn't fully backed by the data?
The choice is to downgrade the class to what the evidence supports or to generate the accuracy and integrity data the claimed class requires. The review sizes that gap early so the decision is made on the supplier's schedule rather than forced by a finding after the application is filed.
Relevant glossary terms
Related pages
Where this fits
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