Transponder TT21 versus TT22 - Considerations

This is the best answer on this thread.

Having flown a turbocharged airplane equipped with TCAS in the teens and low FLs around the west, I missed a lot of aircraft visually that came up In the screen. Flying without it feels like I'm flung blind.

--bob

Here's the reply to my question from Trig. The TT21 does not comply with ADS-B for the 2020 Mandate.
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Dear Walter,

Thank you for your enquiry and for considering Trig.

1. There is no real practical reason to need a TT22, but there is unfortunately a regulatory reason; Our TT21 and TT22 transponders are certified to TSO-C112c and therefore the DO-181D document applies. DO-181D paragraph 1.4.5 states:

Two minimum peak output power levels are supported by this version of these MOPS, 125 watt (21.0 dBW), which is designated as Class 1 equipment, and 70 watts (18.5 dBW), which is designated as Class 2 equipment. For more information on output power levels, see §2.2.3.2.
Class 1 equipment is intended for use in aircraft that operate at altitudes above 15000 ft, or have a maximum cruising true airspeed in excess of 175 kt (324 km/h).
Class 2 equipment may be used in aircraft that operate at altitudes not exceeding 15000 ft, and have a maximum cruising true airspeed not exceeding 175 kt (324 km/h).

Given that you are flying above 15,000ft frequently, the Class 1 TT22 would be more suited to your needs.
2. Cost wise, it may vary slightly depending on the supplier, but the TT22 is usually about $200 more expensive. I would agree with you , I do think collision avoidance is worth being involved in.
3. Not a great deal more power consumption for TT22;
Typical Consumption (at 14 V) TT21 idle: 0.15 A active: 0.28 A
TT22 idle: 0.15A active: 0.34 A

4. To comply with the FAA's 2020 mandate for ADS-B Out a certified Class 1 transponder is required after 2020, so a TT21 would not give a certified ADS-B Out solution. If the FAA decide gliders need to transmit ADS-B out, the TT22 will meet all the requirements. You will need to connect a GPS to the TT22 which provides the positional information and the type of GPS will depend on what the FAA decide is required for gliders.
I would therefore conclude that the Trig TT22 would better satisfy your requirements. I hope this is helpful, but if you have any further questions please do not hesitate to ask.


Bruce Grammon
Trig Avionics Technical Support
Mid-Continent Instruments and Avionics
9400 E. 34th Street North
Wichita, KS 67226
(800) 821-1212 ph
(316) 630-0723 fx
www.mcico.com
www.trig-avionics.com