Electric and hybrid propulsion

This category covers electric motors, inverters, controllers and hybrid powertrains for aircraft. The battery or fuel cell that feeds them has its own guide, and so does the aircraft they are installed in. A buyer here is usually an airframer or an integrator, and the question that decides the programme is not power density. It is what the certification basis will be.

The certification basis is written, not looked up

For conventional products, an applicant shows compliance with the requirements effective on the date of application, plus any special conditions the FAA prescribes.¹ For special classes of aircraft, including the engines and propellers installed on them, where airworthiness standards have not been issued, the applicable requirements are drawn from the portions of existing standards the FAA finds appropriate.¹ That is the sentence an electric propulsion programme lives inside. Piston and turbine engines are certificated as products under Part 33, and that part is written around combustion: ratings and operating limitations, materials, durability, rotor overspeed and engine control systems.² On the airframe side, Part 23 now states outcomes and accepts means of compliance against them, which is why light electric aircraft programmes gravitate to it.³ Ask a supplier which of these routes its hardware has actually been through, and how far.

What to ask about the hardware

Ask for continuous and peak power, and the duration of peak at the temperature and altitude you fly, not at sea level on a bench. Ask for the thermal management assumption, because the cooling system is part of the powertrain whether or not it is on the quote. Ask what the failure modes are at the controller and what the aircraft sees when one occurs: torque loss, uncommanded torque, or a shutdown. Ask what the redundancy architecture is, and what the single points of failure are after redundancy. Ask for the qualification evidence: vibration, altitude, thermal, electromagnetic compatibility, and high voltage insulation coordination. Ask what the maintenance concept is and what the expected life is in cycles rather than hours.

The programme risk is schedule, not physics

Ask how many special conditions the supplier expects on its part of the design, and what the last programme's took. Ask who writes the compliance data, who owns it, and what happens to it if the relationship ends. Ask what the manufacturing readiness is: how many units have been built to the current drawing, on what line, and against what quality system. An electric propulsion supplier with excellent prototypes and no production plan is a real risk to a programme, and a candid supplier will say where it is.

Where the record can be checked

The FAA publishes its design approvals with the searches that reach them, so any type certificate, supplemental type certificate or technical standard order authorisation a supplier claims can be confirmed.⁴ Absence from those registers is not evidence of a bad supplier in this category, because much of the field is pre-certification. It does mean the claim in the pitch deck should be described as what it is: a plan, a test article, or an approval.

Questions that sort suppliers

Ask which certification path the programme is on and who at the FAA or EASA has seen it. Ask for the test hours accumulated on the current configuration. Ask what the production unit will cost at your volume, and at a tenth of it. Ask what the supplier needs from you before it can commit to a date.