(9) Gyroscopic direction indicator (directional gyro or equivalent).
Note that, while it is required that the transponder equipment meet the performance and environmental requirements of the applicable TSO, it is not required that the equipment be manufactured under a TSO authorization.
In theory, this means that you could actually build your own transponder, so long as you can document that it meets the requirements of the applicable TSO.
When someone says an article is “TSO’ed”, what they really mean is that the unit was manufactured under a TSO authorization.
Section 21.601(b)(2) says, “A TSO authorization is an FAA design and production approval issued to the manufacturer of an article which has been found to meet a specific TSO”.
You’ll note that the TSO and TSO authorization deal specifically with design and manufacture, and have nothing to do with installation or operation.
Now we have an idea what a TSO is, but we still haven’t answered the question of whether or not our instruments and avionics in a homebuilt need to be “TSO’ed”.While this is true, our current airspace system as well as the advantages for use in both IFR and VFR operations makes a transponder a popular choice for builders when outfitting their aircraft.The requirements for transponder equipment and operation are found in 91.215, which has this to say: (a) For operations not conducted under part 121 or 135 of this chapter, ATC transponder equipment installed must meet the performance and environmental requirements of any class of TSO-C74b (Mode A) or any class of TSO-C74c (Mode A with altitude reporting capability) as appropriate, or the appropriate class of TSO-C112 (Mode S).Transponders and related equipment; One item that will be high on the list of desired equipment will be a transponder.It’s interesting to note that 91.205 does not list a transponder as required in order to operate under IFR.Minimum requirements The operation of a homebuilt aircraft is most directly governed by its Operating Limitations.