I generally just lurk on the group, but there is enough confusion on this topic that I'm gonna jump in. As an FAA Designated Airworthiness Representative and a provider of ELSA repairman courses, I deal with this subject every day. So, here's the true scoop:
1. From a pure legal standpoint, FAR 91.215(b) requires the use of a transponder with Mode C altitude reporting capability when flying at any altitude within a 30-nm radius of Class B airspace. This is known as the "Mode C ring." It doesn't matter whether you are flying below the floor of the actual Class B airspace--the requirement applies at any altitude within the Mode C ring.
2. An altitude encoder is a device that measures altitude and reports it to the transponder. There are two types of encoders, the "blind" type which has no visible altitude display (it is a small box mounted somewhere behind the instrument panel) and the altitude-reporting altimeter. Either will work and is legal. However, as someone reported, most people use blind encoders because they are much less expensive.
3. FAR 91.215(b) lists an exception that if your aircraft was "originally certificated without an engine-driven electrical system" you don't have to have the transponder and encoder. However, the FAA Light-Sport office interprets that to apply only to engines such as the 65-hp Continental, which never had a generator and where it would be difficult to install one. If you have any modern engine such as a Rotax that has the CAPABILITY of generating electrical power, whether it is connected to the battery or not, the exeption does not apply.
4. If you have an transponder with/without an encoder (whether required or not), FAR 91.413 requires you to have the units tested and certified every two years by an FAA Avionics Repair Station--it generally costs $100-$200.
5. Now, having stated the pure legal stuff, here is the actual real-world situation. If you are operating barely inside the Mode C ring and are staying at pattern altitude, Approach Control may very well not want to be bothered with you. In fact, their radar may not even be able to see you. I based my Piper Colt at Lee's Summit Municipal Airport (LXT), which is two or three miles inside the Kansas City Mode C ring. Since I didn't have a transponder (much less an encoder), I asked the airport manager if I could base the airplane there. He said yes, that Approach Control had said that non-transponder-equipped aircraft could operate from LXT as long as they stayed at pattern altitude and took the most expeditious route out of the Mode C ring.
So, even if you fly within a Mode C ring, my advice is to check with your local airport manager or Approach Control--you may be able to get by without a transponder and encoder.
If you want to learn more about these and many other subjects, I am conducting two fixed-wing ELSA repairman courses, one in the Atlanta area on October 3-4 and another in Yakima, WA on October 17-18. You are welcome to phone or email me about either course. I also invite you to visit my website listed below.
Hope this helps!
Mike
G. Michael Huffman
FAA Designated Airworthiness Representative (DAR)- AP, WS, & PP
Course Provider- ELSA Repairman Inspection- AP, WS, & PP
Course Provider- LSA Maintenance & Inspection for A&Ps
SportAviationSpecialties dot com
sportaviation@gmail.com
904-206-0522
--- In Sport_Aircraft@yahoogroups.com, "Robert D. Taylor" <flydad57@...> wrote:
>
> Is the transponder required regardless?? This IS a bit confusing.
>
>
> ----- Original Message -----
> From: Cy Galley
> To: Sport_Aircraft@yahoogroups.com
> Sent: Wednesday, September 23, 2009 5:06 PM
> Subject: Re: Light-Sport Aircraft Yahoo group Avionics Equipment
>
>
>
> Has to be an engine driven charging system to make you have an encoder.
>
> ----- Original Message -----
> From: Robert D. Taylor
> To: Sport_Aircraft@yahoogroups.com
> Sent: Wednesday, September 23, 2009 2:49 PM
> Subject: Re: Light-Sport Aircraft Yahoo group Avionics Equipment
>
>
>
>
> I believe the "blind" encoder is the device that actually determines the altitude for reporting. Works on static pressure, I think. It feeds the transponder for transmission to ATC.
>
> I will be based just inside the mode C veil surrounding Cleveland class B airspace. Can't get away without one since I'll have a battery and charging system.
>
> Bob Taylor
>
>
>
> ----- Original Message -----
> From: lsotojr1
> To: Sport_Aircraft@yahoogroups.com
> Sent: Wednesday, September 23, 2009 3:39 PM
> Subject: Re: Light-Sport Aircraft Yahoo group Avionics Equipment
>
>
>
> Bob, what's the encoder used for? I too need a transponder. I have a old genave 500 transponder, but i don't know if it will pass a bench test.
>
> --- In Sport_Aircraft@yahoogroups.com, "Robert D. Taylor" <flydad57@> wrote:
> >
> > Mike,
> >
> > Got any good deals on used transponders? I need a cheap one that works. Need the tray, too. And an encoder.
> >
> > Let me know what you might have.
> >
> > Thanks.
> >
> > Bob Taylor
> > Wadsworth, Ohio
> >
> >
> > ----- Original Message -----
> > From: mike
> > To: Sport_Aircraft@yahoogroups.com
> > Sent: Wednesday, September 23, 2009 10:31 AM
> > Subject: Light-Sport Aircraft Yahoo group Avionics Equipment
> >
> >
> > Anyone in need of any New or Used avionics equipment I can be reached here or at 941-360-6877 Ext.131
> >
> > Thanks
> > Mike Swiader
> >
>
>
>
>
>
>
>
>
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