Does FLARM meet TABS requirement?

On Saturday, August 8, 2015 at 11:44:09 PM UTC-7, wrote:
Darryl, I don't know how you can manage to keep on top of all this ADS-B stuff without your head exploding but thank you for doing so! Whenever I try to make sense of it all it makes me want to give up flying and take up Tiddlywinks or something.

Out of curiosity, what performance parameters in the PowerFLARM system make it a "degraded" GPS source unsuitable for ADS-B out? I assume the system must be accurate enough for airborne traffic awareness and collision warnings as it has proven satisfactory in FLARM to FLARM situations.

Everybody keeps thinking first about GPS accuracy, accuracy is just a small part of what makes a high-end aviation GPS like a TSO-C145c device. It's reliability, failure detection and predictability of that reliability that separate these from consumer devices.

A TSO'ed/IFR GPS source used to meet the FAA 2020 Mandate such as TSO-C145c has to support RAIM for reliability purposes. PowerFLARM's consumer chipset based GPS source cannot do that.... and RAIM and other goodies are not transmitted over NMEA. TABS/TSO-C199 Class B GPS sources do away with the RAIM requirement (it's actually one of the big good things in that TSO).


TABS/TSO-C199 Class A (the transponder/1090ES Out part) use HFOM (Horizontal Figure of Merit) and VFOM (Vertical Figure of Merit) for "GPS health", but NMEA does not send HFOM or VFOM data. That is why the TSO allows the Class A TABS device to calculate HFOM and VFOM from HDOP and VDOP which NMEA does provide (in $GPGSA). Or course a TSO-C199 Class B device might use NMEA, Aviation serial, NexNav serial binary, etc.

It's worth noting that the first GPS product announced that is targeted at TABS Class B GPS source use is the NexNav Micro-i, and few details are available so far, but I expect it will transmit GPS data on both NexNav serial binary and NMEA serial links as their similar products do, and it does include RAIM support (which would require use of the NexNav binary serial link.... which the Trig TT-21/22 already support) even though that is not required for TABS... NexNav have likely largely just repackaged another of their products at reduced price.