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Do I need a transponder on my Rotax powered aircraft?

I am often asked if a Rotax powered airplane needs to have a transponder, in accordance with 14 CFR 91.215. This also applies to ADS-B equipment requirements, in accordance with 14 CFR 91.225.

Some people think that the Rotax engine does not have an "engine driven electrical system" as defined in 14 CFR 91.215(b)(3). Some people think the regulations state that the electrical system must be "belt driven", or think it doesn't apply to us because we have a "lighting coil". That is not what the regulations say. The regulations only say that the system must be "engine driven". The regulations do not care what kind of engine-driven device you have (such as an alternator, generator, or a lighting coil).

If you "use" the lighting coil in your Rotax to power electrical equipment on your aircraft (starter, lights, radio, etc.), then yes, you are required to have a transponder, to fly in those areas where one is normally required.

The regulations exempt "any aircraft which was not originally certificated with an engine-driven electrical system or which has not subsequently been certified..."

If you had an electrical system on your airplane the day you received your airworthiness certificate, then your airplane was "originally certificated" with an electrical system, and you are required to have a transponder if you want to fly in the areas where they are required.

If your airplane did not have an electrical system when it received its airworthiness certificate, but you later install one, you are still required to comply. On an experimental, you (self) certify the transponder installation, when you proclaim the aircraft airworthy with a logbook endorsement showing the installation. This satisfies the "subsequently been certified" portion of the regulation.

Here is a letter from the FAA, dated August 22, 2005, clarifying the transponder/electrical system definitions: View the letter here. You can also confirm the FAA's position on this, by contacting the FAA Light Sport Aircraft Branch in Oklahoma City, OK., at (405) 954-6400.

There are provisions for the ATC facility manager to issue waivers to the rule, if they choose to do so. Guidance can be found in FAA Order 7210.3Z.

Besides being legal, it's equally important to be safe. The FAA mandates transponders in certain airspace, for a reason. Without one, many small aircraft (especially the "ultralight-like" ones) are just not visible on radar. Why wouldn't you want to do everything you can, to make yourself visible to ATC and other aircraft?

Note: Although I reference Rotax on this page, the rules apply to any manufacturer of engine.


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This page updated on: February 24, 2019
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