Current Level of GA Equipage with Avionics required for ADS-B

Under the final ADS-B Out rule, aircraft are required to have the following equipment onboard the aircraft:

1. Navigation (or Position) Source

This component is what determines the position as well as velocity of the aircraft that is then broadcast via the ADS-B message. Contrary to what many pilots think, this doesn’t have to be a GPS. The final rule only states the parameters that have to be satisfied by this equipment; for example the horizontal position accuracy has to be less than 0.05NM and the velocity accuracy has to be less than 10 meters per second. As long as the position source meets these and requirements in the rule, it can be used as for ADS-B.
However, from a General Aviation perspective, this position source will most likely be a GPS. Also, the only stand-alone (that is, non-coupled) navigation equipment today that can satisfy the requirements in the rule is a WAAS enabled GPS in accordance with any revision of TSO-C146.
Current Percentage of TSO-C146 GPS in GA Fleet: 17.86%*

Update: As Henry Billingsley from Free Flight System correctly noted, any revision of TSO-C146 can be used to comply with this requirement. This post has been corrected accordingly. Appendix 2 of Advisory Circular AC-20-165 has more details.

2. ADS-B Avionics

Using the position information from the navigation source, altitude from the altimeter and other hard coded information, this component creates the actual ADS-B message.
For UAT ADS-B avionics, this would be a stand-alone box where for 1090ES ADS-B this function would be performed by the transponder.
As stated in the final rule, this component needs to satisfy TSO-154c (UAT) or TSO-166b (1090ES).
Current Percentage of TSO-154c ADS-B Avionics in GA Fleet: 0%* Current Percentage of TSO-154c ADS-B Avionics in GA Fleet: 0%*

2. Transponder

Though many suggested removing the requirement for a transponder after ADS-B is mandated, the final rule did not adopt that suggestion. One of the reasons the FAA does not want to remove transponders right away is that without them, in case of a GPS or ADS-B outage, ATC would not be able to control traffic were it not for secondary radar.
For ADS-B, you’ll either continue using your existing Mode A/C Transponder alongside with a standalone ADS-B unit, or, you upgrade an existing Mode S Transponder to 1090ES ADS-B.

Current Percentage of Mode A/C Transponder Equipage in GA Fleet: 83.67% Current Percentage of Mode S Transponder Equipage in GA Fleet: 10.51%

3. Antenna: ADS-B and Transponder

ADS-B signals need to be transmitted via an antenna. The proposed rule suggested that everybody install two antennas: one at the top of the aircraft to be used for ADS-B In communications with other aircraft above you as well as one antenna on the belly of the aircraft for transmissions to the ground/other aircraft below you.
(Having these two antennas is called antenna diversity).
After much pushback by the industry, the final rule now only requires ADS-B to be transmitted from a single antenna at the bottom of the aircraft.
To further minimize the cost of an ADS-B installation, the FAA included a technical specification in the UAT ADS-B standard that allows sharing of a single antenna between the transponder and the ADS-B unit. This device is called an antenna diplexer.
Bottom Line: If you have a transponder, you will not have to install a new antenna. All you’ll need is an antenna diplexer.
However, having only a bottom antenna will reduce your visibility to/of other aircraft that fly above you which may result in reduced benefit as some of the proposed ADS-B applications will not work as well without Antenna Diversity.
Current Percentage of Antenna Diplexer Equipage in GA Fleet: 0% Current Percentage of Antenna Diversity Equipage in GA Fleet: 10.51%**

5. Altitude Encoding Altimeter

Lastly, the final rule states that the altitude information transmitted in the ADS-B message has to come from the same source as the altitude transmitted by the transponder. This indirectly results in a requirement for some kind of altitude encoding altimeter.

Current Percentage of Altitude Encoding Altimeter Equipage in GA Fleet: 87.29%***

Note: All percentages are based on the 2007 FAA Avionics survey. In it, some operators reported ADS-B equipment. This equipment is what is called “Legacy ADS-B Equipment” and it is not in accordance with the final rule. It may be possible to upgrade this equipment to the respective TSO’s.

*Standard was published after 2007, I could not find any manufacturers that currently manufacture equipment to this standard (in Aug 2010).
** Based on Mode S Transponder equipage – Mode S usually has antenna diversity.
*** Based on Mode C and Mode S Transponder equipage.