Power supply equipment STC installation certification support

When this review is needed

• New equipment adds meaningful load and the aircraft's electrical load analysis has not been updated for the worst-case bus condition.
• The unit sits in a bay with limited cooling and its thermal performance at that location is unconfirmed.
• Circuit protection and wire sizing for the new feeder have not been substantiated against the bus.
• The applicant needs to know which installation findings the equipment's TSO data covers and which are new to this airframe.

The problem

Installing a power supply is as much an electrical-system question as an equipment question. The added load has to fit inside the aircraft's generation and distribution capacity under the worst-case bus configuration, the unit has to stay within thermal limits wherever it is bolted, and the new feeder needs protection and wire sizing that the aircraft's electrical scheme supports. Modifiers often hold clean equipment data but have not closed the load analysis, the cooling substantiation, and the wiring findings that the installation itself raises.

What gets reviewed

• Electrical load analysis updated for the added equipment under worst-case bus and generation conditions
• Thermal and cooling substantiation at the actual installed bay and its airflow
• Circuit protection, wire sizing, and feeder routing for the new load
• Bonding and grounding of the equipment to airframe structure
• Installation effects on the electrical system, including load shedding and abnormal bus configurations
• A trace from each electrical-installation requirement to the analysis or test that closes it

What gets validated

• The load analysis reflects the worst-case bus configuration, including a generator-out condition, not just normal operation
• Thermal substantiation reflects the airflow and ambient of the actual installed bay
• Circuit protection and wire gauge match the load and the aircraft's electrical scheme
• Bonding path and impedance to structure are substantiated for the installed location
• Each installation finding names the analysis, drawing, or test that closes it

Evidence normally required

• The modification's certification basis and any special conditions carried by the target airframe
• The power supply's TSO or qualification data package
• The aircraft's electrical load analysis and generation capacity data
• Installation drawings, mounting bay details, and cooling provisions
• Wiring diagrams, circuit protection scheme, and bonding data for the aircraft

Common discrepancies

• A load analysis updated for normal operation but not for the generator-out or emergency bus case
• Thermal performance assumed from the bench rather than substantiated for the confined installed bay
• Feeder wire sizing or circuit protection that does not match the aircraft's electrical scheme
• Bonding to structure left unsubstantiated where the mounting sits on a painted or composite surface

What is at stake

A power supply STC filed without a complete load analysis or cooling substantiation stalls when the authority asks whether the electrical system tolerates the new load under a generator-out case, or whether the unit stays within limits in its actual bay. Reopening those after filing can force a load survey, a thermal rework, or a feeder redesign on a program with a booked installation slot, and the downtime moves with the approval.

How the work runs

What the buyer receives

• A gap list of the open electrical-installation findings, ordered by their effect on the schedule
• A trace map from each installation requirement to the substantiating analysis, drawing, or test
• A closure sequence ordering the electrical, thermal, and wiring work still owed

Who uses the output

• Certification engineers building the power supply installation compliance package
• Electrical systems engineers scoping the load and wiring work still required
• Program managers fitting the closure work to the aircraft's booked installation slot

How the work fits into the transaction or program

The review connects the equipment's qualification to the aircraft's electrical system. It substantiates the added load, the cooling, and the wiring against the modification's certification basis, so the STC package the applicant files already answers the electrical-system questions an authority raises rather than surfacing them during review.

Jurisdiction-specific considerations

FAA and EASA can differ on how the electrical load analysis must treat abnormal bus configurations and on the acceptable means for wiring substantiation, and a validation can reopen a load or wiring finding the first authority accepted. The review flags the findings most likely to be read differently so one evidence set can serve both paths.

Regulatory limits

This work assesses whether the installation evidence supports the STC's findings. It does not issue an airworthiness determination, grant or hold the STC, or approve the modification, and it does not replace the authority's review.

What this review does not cover

• Producing the electrical load analysis or the wiring design
• Running the thermal or electrical installation tests
• Acting as the STC applicant or holding the design approval

Specific to this review

• The load a power supply adds is judged against the worst-case bus, not normal operation, so a generator-out case usually drives the load finding.
• A unit within thermal limits on the bench can exceed them in a confined bay with poor airflow, so cooling is an installation finding, not a box-level one.
• Feeder wire sizing and circuit protection are properties of the aircraft's scheme, so the same equipment can need different protection on different airframes.
• Bonding to a painted or composite mounting surface is a frequent open finding because the impedance path back to structure is not obvious.

Sources

Frequently asked questions

Relevant glossary terms

Related pages

Where this fits