Part 25 navigation
Part 25 certification basis support for navigation equipment
This support connects a navigation system's evidence to the Part 25 certification basis of the transport-category aircraft it serves. Suppliers and modifiers use it when a navigation unit built to a performance standard has to answer a transport-category basis, where the operational credit, the redundancy expected of the function, and the integrity of the position feeding it are all judged more strictly. The work checks sensor input handling, database currency and integrity, the software level against the failure effect, and alignment with the applicable minimum operational performance standards, then reconciles them to the named basis paragraphs. You receive a navigation basis map, a list of items the evidence leaves open, and an ordered path to close them.
When this review is needed
- A navigation unit built to a performance standard is going into a transport-category aircraft and its evidence has to answer the Part 25 basis.
- The operational credit sought carries a redundancy or availability expectation the transport-category basis imposes.
- The integrity of the position source has to be substantiated for the credit being claimed on the aircraft.
- A finding questions how the navigation function's software level and database handling meet a named Part 25 paragraph.
The problem
The transport-category basis expects more of a navigation function than the performance standard the unit was built to. Part 25 asks about availability and redundancy for the credit claimed, about the integrity of the position through the whole chain, and about how the function behaves when an input drops out, and the performance-standard case rarely reaches those questions. The evidence for redundancy and continuity often lives at the aircraft integration level, outside the unit file the supplier brings.
What gets reviewed
- The Part 25 basis paragraphs the navigation function answers at the aircraft's amendment level
- Sensor input handling and the continuity of the function when an input is lost
- Navigation database currency, integrity, and the response to a stale or corrupt load
- The software level against the failure effect of a misleading navigation output at transport scale
- Availability and redundancy expectations attached to the operational credit being claimed
- Alignment with the applicable minimum operational performance standard for that credit
What gets validated
- Each navigation basis paragraph has evidence assigned, including the availability and redundancy items
- Sensor input handling and function continuity on a lost input are substantiated for the credit claimed
- Database currency and integrity handling is tested, including the response to a corrupt load
- The software level matches the failure effect of a misleading navigation output at transport scale
- The operational credit traces to the minimum operational performance standard and its availability expectation
Evidence normally required
- The certification basis for the transport-category aircraft and its amendment level
- The navigation equipment performance and environmental qualification reports
- The software lifecycle summary and the assigned software level
- The database architecture, currency handling, and integrity design
- The operational credit being sought and the redundancy and availability architecture behind it
Common discrepancies
- An availability or redundancy expectation for the credit with no integration-level evidence behind it
- Function continuity on a lost input assumed rather than substantiated for the transport-category credit
- A software level set below the failure effect of a misleading output at transport scale
- Database integrity handling described but never tested against a corrupt load
What is at stake
A navigation package built on the performance standard alone can satisfy its own bench case and still miss the availability, redundancy, and integrity items the Part 25 basis attaches to the operational credit. When those surface as findings, the fix reaches into the integration architecture or the software assurance, and reworking either on a transport-category program is costly once the installation is otherwise closed.
Move from findings to resolution
Identify gaps against the means of compliance.
How the work runs
Fix the credit and basis
Establish the operational credit sought and the Part 25 basis paragraphs, including availability and redundancy, the navigation function must answer.
Trace continuity and integrity
Follow input handling, continuity on a lost input, and database integrity into the evidence and mark where the trace stops.
Reconcile level and redundancy
Match the software level to the misleading-output effect and the redundancy evidence to the credit's availability expectation.
Order the closure
Prioritize the gaps that gate the credit and deliver a basis map for the matrix.
What the buyer receives
- A basis map linking each relevant Part 25 paragraph to the navigation evidence behind it
- A gap list emphasizing availability, redundancy, and integrity items tied to the credit
- A closure sequence prioritizing the gaps that gate the operational credit
Who uses the output
- Certification leads building the navigation compliance argument for a transport-category submittal
- Engineering teams substantiating redundancy, continuity, and integrity to the basis
- Compliance managers defending the operational credit against a Part 25 finding
How the work fits into the transaction or program
The mapping bridges the navigation performance case and the transport-category submittal, turning a MOPS-based argument into basis-level compliance including the availability and redundancy the credit carries. Its gap list steers the integration and software work, and the basis map populates the compliance matrix the applicant carries forward.
Start with a single asset
Confirm requirements trace through verification.
Aircraft-specific considerations
On a transport-category aircraft the navigation credit usually depends on redundancy that lives in the aircraft architecture, so a unit adequate on its own may still need dual-source or cross-monitor evidence to meet the credit. The mapping is scoped to the aircraft's navigation architecture, because the availability and integrity the basis demands follow from how the function is built up on this type.
Jurisdiction-specific considerations
FAA and EASA reference navigation performance standards that largely align but differ in accepted credits and in the availability and continuity expectations invoked, so a navigation argument accepted under one basis can need supplement under the other. The mapping flags where the credit and its supporting evidence change between authorities.
Regulatory limits
The work reconciles navigation evidence to the Part 25 basis and marks the shortfalls. It grants no operational credit, makes no compliance finding, and issues no approval. The authority grants the credit and the applicant owns the claim.
What this review does not cover
- Granting or approving any operational credit or navigation authorization
- Running the navigation performance or flight-test campaign itself
- Any airworthiness determination on the installed navigation equipment
Specific to this review
- At transport scale the operational credit usually carries an availability or redundancy expectation, so a single-source navigation argument leaves those Part 25 items open.
- Function continuity on a lost input is a distinct basis question the performance standard does not answer, and it lives at the integration level rather than in the unit file.
- The failure effect of a misleading navigation output is weightier on a transport-category aircraft, which can push the software level above what the unit was originally built to.
Sources
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. FAA type certification process, certification basis establishment, and compliance findings.
SAE International. Development assurance process at aircraft and system level, including requirements capture and validation.
Frequently asked questions
The navigation unit meets its MOPS. Why does Part 25 ask for more?
A MOPS sets minimum equipment performance. The Part 25 basis attaches availability, redundancy, and integrity expectations to the operational credit, and those usually depend on the aircraft architecture. The mapping shows where meeting the MOPS still leaves transport-category basis items open.
Relevant glossary terms
Related pages
Where this fits
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