Part 25 communication
Part 25 certification basis support for communication equipment
This support maps a communication installation's evidence onto the Part 25 certification basis of the transport-category aircraft it serves. Suppliers and modifiers installing radios and their antennas use it when the box meets its standard but the installed function has to answer a transport-category basis, where electrical integration into a large distribution system, antenna coexistence across a busy airframe, and radio availability are judged more strictly. The work checks installed radio performance, antenna placement and coexistence, the load against the aircraft's electrical system, and the environmental case for the location, then ties each to the basis paragraph it addresses. You receive a communication basis map, a list of open items, and an ordered plan to close them.
When this review is needed
- A radio installation on a transport-category aircraft needs its evidence tied to the Part 25 basis.
- The new radio has to coexist with a crowded antenna farm and the coexistence has to be substantiated.
- The added load has to integrate into a large electrical distribution system without eroding required margins.
- A finding asks how the installed communication function and its availability meet a named Part 25 paragraph.
The problem
On a transport-category aircraft the communication basis is less about the radio and more about how it lives on a busy airframe. A large aircraft already carries many antennas, so a new radio has to coexist without degrading or being degraded by its neighbors, and its load integrates into a distribution system with load-shedding logic and redundancy rules the box case never saw. Radio availability expectations attach to the function at transport scale, and none of that is answered by the equipment qualification the supplier brings.
What gets reviewed
- The Part 25 basis paragraphs the communication function answers at the aircraft's amendment level
- Installed radio transmit and receive performance in the antenna and cable configuration
- Antenna coexistence across the airframe's antenna farm and the interference budget
- Electrical integration into the distribution system, including load-shedding and redundancy rules
- Environmental qualification against the installed location and its conditions
- The gap between installed performance and the bench performance the package assumes carries over
What gets validated
- Each communication basis paragraph has installed-configuration evidence, including coexistence
- Radio performance is confirmed at the installed antenna and cable, accounting for real cable loss
- Antenna coexistence with the existing antenna farm is substantiated against an interference budget
- The added load integrates into the distribution system without eroding required margins or breaking shedding logic
- Environmental qualification categories match the installed location and its conditions
Evidence normally required
- The certification basis for the transport-category aircraft and its amendment level
- The communication equipment performance and environmental qualification reports
- Antenna placement drawings, the existing antenna farm layout, and cable routing
- The aircraft electrical load analysis, distribution architecture, and load-shedding rules
- Installation substantiation for bonding, interference, and system interaction
Common discrepancies
- Antenna coexistence with the existing farm assumed rather than substantiated against an interference budget
- An added load that integrates without regard to the aircraft's load-shedding logic
- Installed radio performance asserted from bench data without accounting for cable loss on long runs
- Environmental qualification categories that undershoot the installed location on a large airframe
What is at stake
A communication package that answers the radio standard but not the transport-category installation basis leaves coexistence, electrical integration, and availability to surface as findings. A coexistence problem discovered late can force antenna relocation on a large airframe, and an electrical integration gap can reach into load-shedding logic, both of which are expensive to correct once the aircraft is built up and the program is near its certification date.
Move from findings to resolution
Identify gaps against the means of compliance.
How the work runs
Anchor the transport basis
Establish the Part 25 basis paragraphs the communication function answers for this aircraft and its amendment level.
Trace coexistence and load
Point radio, antenna-farm, and electrical evidence at the paragraphs and mark where coexistence or integration is only assumed.
Substantiate the installation
Check installed radio performance, antenna coexistence, and load integration against the actual airframe and distribution system.
Rank the closure
Order the gaps by the rework each forces and hand off a basis map for the matrix.
What the buyer receives
- A basis map linking each relevant Part 25 paragraph to the communication installation evidence
- A gap list emphasizing antenna coexistence and electrical integration
- A closure sequence ordering the gaps by the airframe or electrical rework each implies
Who uses the output
- Certification leads building the communication compliance argument for a transport-category modification
- Engineering teams substantiating antenna coexistence and electrical integration
- Compliance managers responding to a finding on the installed communication function
How the work fits into the transaction or program
The mapping ties the radio performance file to the transport-category installation basis, where coexistence and electrical integration decide compliance on a busy airframe. Its gap list drives the coexistence and load-integration work, and the basis map populates the compliance matrix the applicant carries into review.
Start with a single asset
Confirm requirements trace through verification.
Aircraft-specific considerations
A transport-category airframe carries a dense antenna farm and a structured electrical distribution system, so a new radio has to fit into both rather than sit alone. Long cable runs also make installed performance diverge from the bench more than on a small aircraft. The mapping is scoped to the aircraft's antenna layout and distribution architecture, because coexistence and integration are what the transport-category basis asks about.
Jurisdiction-specific considerations
FAA and EASA communication requirements align on radio performance but differ in some installation, coexistence, and spurious-emission expectations, so a communication install accepted under one basis can need supplement for the other. The mapping notes where the installation and coexistence evidence changes between authorities.
Regulatory limits
The work maps communication evidence to the Part 25 basis and marks the gaps. It makes no compliance finding, issues no radio authorization or approval, and does not determine that the installation is airworthy. Those decisions rest with the applicant and the authority.
What this review does not cover
- Granting any radio station authorization, operational approval, or design approval
- Running the installed coexistence test or the electrical integration analysis itself
- Any airworthiness determination on the installed communication equipment
Specific to this review
- On a transport-category airframe the communication basis centers on coexistence: a new radio has to share a crowded antenna farm without degrading or being degraded by its neighbors.
- The added load integrates into a distribution system with shedding and redundancy rules, so a load that looks small can still break a basis item by upsetting the shedding logic.
- Long cable runs on a large aircraft make installed radio performance diverge from the bench more than on a small airframe, so bench data alone leaves the installed-performance item open.
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 radio meets its standard. Why does Part 25 focus on the antenna farm and electrical system?
The standard covers the radio. The Part 25 basis asks how it lives on a busy transport-category airframe, where it must coexist with many antennas and integrate into a structured electrical system. The mapping shows where meeting the radio standard still leaves those installation items open.
Relevant glossary terms
Related pages
Where this fits
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