Avionics work on an aircraft and when an upgrade is required

01 What avionics work actually involves

Avionics is the collection of electronic systems an aircraft carries: communications, navigation, surveillance, flight instruments and the automatic systems that tie them together. When people in the industry talk about avionics work, they mean two different jobs at once. One is the bench and line work of installing, wiring, testing and repairing that equipment. The other is the paperwork that proves the installation is approved for the aircraft it sits in. Both have to happen before a single new screen lights up in a cockpit. The requirements that govern the second job are the ones that push an aircraft toward an upgrade, and they come from the Federal Aviation Administration.

02 Communication, navigation, surveillance, and instruments

The equipment itself breaks into families. Radios handle voice and data communication. Navigation systems guide the aircraft along a route. Surveillance equipment tells others where the aircraft is. Flight instruments show the crew what the aircraft is doing. On top of those, an increasing share of the work concerns software and airborne electronic hardware, which the FAA treats as its own category of concern. Automatic systems that control or assist flight sit in the same bucket, because they depend on the same wiring, power and data buses that the other systems use.

03 Under what approvals does that equipment fly?

An avionics item rarely reaches an aircraft as a finished product approved on its own. The FAA's design approval routes give it a place to sit. A Technical Standard Order is one such route, and the FAA publishes a search tool for the TSOs already issued. A Parts Manufacturer Approval is another, with its own searchable list. Some equipment is approved as Non-Required Safety Enhancing Equipment under 14 CFR 21.8(d), a route for items that go beyond what the regulations require. Others arrive through the broader design approval process covered on the FAA's design approvals page, which gathers the pathways an applicant can follow.

04 How an alteration becomes an approved change

Putting a new system into an existing aircraft is an alteration, and alterations live under the same design approval structure as the original aircraft. A Supplemental Type Certificate is the standard route for a change that departs from the type design. Field approvals handle smaller cases. Where the change touches the original design itself, an amended Type Certificate comes into play. The FAA also points applicants at its product issues lists and at FAA Order 8110.4 on type certification, which describes the original approval process in detail. None of these routes is casual: each asks the applicant to show that the altered aircraft still conforms to an approved design.

05 The company that holds the approval

The holder can be an operator, a repair station, or a specialist shop. The FAA keeps a guide to product certification written jointly with industry, aimed at people on both sides of the application. It also keeps a technical training program for the staff who work certification questions, and a program of senior technical experts for cases that need deeper review. That machinery exists because the approval is not a one-time event. It attaches to a design and to a holder, and both are expected to answer questions for as long as the product stays in service.

06 Where conformity and inspection fit in

Approval of a design is only half the story. The FAA runs a National Automated Conformity Inspection Process, which speaks to the other half: showing that the physical article matches what was approved. Type Certificate Data Sheets record the approved characteristics of an aircraft type. On the maintenance side, a repair station approval under Part 145 governs who may perform work on the installed equipment, and a major repair or alteration is recorded on Form 337. A bench test that passes means little if the installation record does not line up with the approved design.

07 What pushes an aircraft toward an upgrade?

Three forces tend to move an owner or operator off the current fit. The first is a regulatory requirement that changes what the aircraft must carry, whether that lands as an airworthiness directive or as a rule that alters the certification basis. The second is equipment that can no longer be supported, where a manufacturer stops producing or repairing a box that the aircraft still needs. The third is a capability the operator wants but the current installation cannot deliver, often because the old wiring and data paths will not carry the newer systems. A single upgrade can trigger all three at once, because changing one system on a shared bus affects everything else connected to it.

08 Why the smallest change can pull in the whole panel

A new radio does not fly alone. It needs power, a place in the panel, an antenna, and a path to the other systems that will use its data. If the new unit speaks a different data format, the boxes around it may need to change as well. The FAA's design approval categories reflect this: airships, engines and propellers including auxiliary power units, piloted balloons, rotorcraft, small airplanes, transport airplanes and unmanned aircraft each carry their own set of expectations. The category sets the baseline, and the alteration adds to it. That is why an owner who sets out to replace one instrument sometimes ends up with an approved change touching several systems.

09 Where to look for the approval behind a piece of equipment

An owner, a buyer or a maintenance planner who wants to know whether a given item is approved for a given aircraft has public entry points. The FAA publishes search tools for Supplemental Type Certificates, for Parts Manufacturer Approvals and for Technical Standard Orders, and it publishes Type Certificate Data Sheets. An application for an airworthiness certificate goes on Form 8130-6, and an authorized release for a part travels on Form 8130-3. Before any of that, an applicant who wants to add or change a design starts from the information the FAA addresses to applicants and design approval holders, and from the list of designees and delegations who can act on the agency's behalf.

10 The approval outlasts the install

Design approval work does not end when the aircraft flies. The FAA keeps its design approval resources open for the life of the product, and it points readers at its human factors work in aviation safety, at software and airborne electronic hardware guidance, and at the training routes built around certification. A shop that installs avionics is really maintaining a chain of documents: the approved design, the conformity record, the release tag, the entry in the aircraft log. Break that chain and the equipment may be installed and still not approved. The FAA's federal programs that shape aviation work carry the wider context, and the agencies that regulate United States aviation set the rules the chain has to satisfy.

Federal Aviation Administration, Design Approvals (faa.gov/aircraft/air_cert/design_approvals): this is the agency page that gathers the routes for approving aircraft designs and their changes.

It collects the original type certification process, amended type certificates, supplemental type certificates, field approvals, parts manufacturer approvals, technical standard orders, and the approvals for non-required safety enhancing equipment, with a search tool for each of the last three.

It also groups the aircraft and product categories, from small airplanes and transport airplanes to rotorcraft, balloons, airships, engines and propellers, and unmanned aircraft, and lists resources for applicants, designees and delegations.

11 Where to continue

The pages below take avionics work on an aircraft and when an upgrade is required a step further inside operations and upkeep, beginning with What a Part 135 operator is and how it is structured, then move on to the next trade. Each one names the agency that holds the rule it describes.