On Tuesday, June 16, 2015 at 1:44:47 PM UTC-4, Steve Leonard wrote:

On Tuesday, June 16, 2015 at 12:19:19 PM UTC-5, son_of_flubber wrote:

Is it reasonable to argue that a Trig TT21 (130 watt) should be acceptable for glider use due to my lower speed, rather than just the TT22 (250 watt)? Is there any chance that the FAA would grandfather in TT21s in any new regulations?


Son, your transponder (TT21) is already acceptable. No need to "grandfather" it.


My limited understanding... Due to the 130 watt output, the TT21 is not 2020 compliant, so even if I invested in a TSO'd GPS source, I could not use the TT21's ADS-B out capability. The 250 watt 2020 requirement is based on the closing speed of two aircraft and since a glider is slow (or stationary in wave) I'd conjecture that it was not needed. ADS-B out at 130 watts is much better than no ADS-B out.

From Trig website:

What are the differences between the TT21 and TT22?
Both models have the same physical dimensions and advantages of size and ease of installation. The TT21 is a 130 watt Class 2 transponder; this makes it ideal for light sports and regular GA use. The TT22 is a 250 watt Class 1 transponder, ideally suited to higher performance and/or high altitude performance types.
In the U.S. the FAA has stated that Class 1 transponders must be used to be '2020 complaint' For U.S. customers Trig recommends the TT22 unit for this reason.