ADSB?

[L16 Pilot]

Kind of like "aircraft radios". When I had my Cherokee I spent a pile of $$$ trying to keep the (TSO'd) radios working. Now I fly with a $250 handheld that actually keeps working and not TSO'd by the way.

[cub builder]

Yeah, they do. If you read their blog, they've submitted to the FAA twice now - the 2nd time in January. If they didn't believe that they met the standard, they wouldn't have submitted, because the paperwork is a PITA.

From their web site one could deduce that it likely meets performance standards since they submitted for TSO Authorization. However, the TSO testing is with a different GPS puck and different antenna from what is being sold as a "portable" unit. I haven't read their blog as it is closed to those not registered.

Soon is relative :-). They say that it's in the FAA's hands now, and they expect a 2nd round of request for more info, so I'd bet it's many months before approval.

Again, that is for the TSO certification. Their units likely currently meet the TSO performance standard with their current GPS puck and "portable" antenna mounted internally in my wood and glass plane.

I certainly hope you're correct.

I bet my money on it several months ago when I bought one of their units. Once I see a statement on their web site stating that they meet the performance standards, I'll buy a second unit for my Exp SuperCub. Since meeting the performance standard makes it 2020 legal for the E-AB and LSA Aircraft, they may not necessarily even want to get the TSO certification unless their projected sales warrant it. Wish I could say that I foresaw this change in the FAA's interpretation of their rule, but I didn't. I decided I would like to have the weather and traffic data in flight now and would worry about 2020 in 2020. It's been my plan all along to continue using this unit as I don't spend much time in Class B or C airspace anyway.

-Cub Builder

[MEdwards]

People here are assuming the Skyguard unit meets the required TSO performance specifications. There's an easy way to find out. The FAA offers to send users a report showing whether their ADS-B Out transmissions met the specs on a particular flight. All you have to do is send an email asking for one. The email address is:

9-AWA-AFS-300-ADSB-AvionicsCheck@faa.gov

Supposedly, you need to include the N number, date, time, type of installed equipment (navigator and ADS-B solution), as well as departure or nearby airports. I have also heard people say all they gave was their N-number and they got the report back within hours.

[Gunslinger37]

You have touched upon one of the problems with a "portable" ADS-B that could be moved from aircraft-to-aircraft. If someone like Garmin were to make a ADS-B OUT version of their GDL 39, they would need a way for the Broadcast Message Elements to be entered into the device, so that the aircraft N number and base 16 hex code could be transmitted.

BTW did you see that NavWorx just announced a "fully compliant" ADS-B In/Out for $699. The same unit with TSO sells for $2500.

[cub builder]

You have touched upon one of the problems with a "portable" ADS-B that could be moved from aircraft-to-aircraft. If someone like Garmin were to make a ADS-B OUT version of their GDL 39, they would need a way for the Broadcast Message Elements to be entered into the device, so that the aircraft N number and base 16 hex code could be transmitted.

BTW did you see that NavWorx just announced a "fully compliant" ADS-B In/Out for $699. The same unit with TSO sells for $2500.

Imagine that? Navworx reacted to the FAAs change to the market to take advantage.

The portable ADS-B Out units have an app already installed in your GPS software so you can change the Broadcast Message Elements. When my iFly (or iFly software on my Droid) sees one of the many ADS-B out devices it can work with, it enables an app on the GPS that I can select to configure the ADS-B unit. I would assume most of the other GPS softwqaare packages have preloaded ADS-B out control apps in them.

Question on the ADS-B units for someone that knows more about this than me. Flying with ADS-B traffic, I see altitudes reported all over the place and usually incorrectly. My SkyGuard unit is broadcasting WAAS GPS derived altitude. The Navworx unit ties into an altitude encoder so reports pressure altitude. Aircraft broadcasting Mode-C are reporting pressure altitude, but that is picked up by Center's radar and apparently has a Barometric Pressure Correction applied before broadcasting traffic information out via the ADS-B tower. Due to the variable terrain in my part of the country, the corrected Mode C altitudes for the traffic that is rebroadcast from the ADS-B towers is also usually off by 200 - 400'. My observation is that the altitude reporting for traffic seems to be all over the map, usually with errors of 200 - 400'. So how does the ADS-B performance spec say the altitude is to be derived? If it is to be pressure altitude, then the Skyguard unit can't comply. Or does the performance spec even say? We know Skyguard has submitted their equipment for evaluation, so they apparently think they comply. Or perhaps the FAA assumes GPS altitude, pressure altitude and corrected pressure altitude are close enough even though they want to require WAAS III for position??? I'll be curious to see what you guys that like to delve into the regs can derive.

-Cub Builder

[TedK]

Question on the ADS-B units for someone that knows more about this than me. Flying with ADS-B traffic, I see altitudes reported all over the place and usually incorrectly. My SkyGuard unit is broadcasting WAAS GPS derived altitude. The Navworx unit ties into an altitude encoder so reports pressure altitude. Aircraft broadcasting Mode-C are reporting pressure altitude, but that is picked up by Center's radar and apparently has a Barometric Pressure Correction applied before broadcasting traffic information out via the ADS-B tower. Due to the variable terrain in my part of the country, the corrected Mode C altitudes for the traffic that is rebroadcast from the ADS-B towers is also usually off by 200 - 400'. My observation is that the altitude reporting for traffic seems to be all over the map, usually with errors of 200 - 400'. So how does the ADS-B performance spec say the altitude is to be derived? If it is to be pressure altitude, then the Skyguard unit can't comply. Or does the performance spec even say? We know Skyguard has submitted their equipment for evaluation, so they apparently think they comply. Or perhaps the FAA assumes GPS altitude, pressure altitude and corrected pressure altitude are close enough even though they want to require WAAS III for position??? I'll be curious to see what you guys that like to delve into the regs can derive.

-Cub Builder

ADS-B Out is required to be integrated to a Pressure Encoder, and it has to be the same Encoder that is feeding the Mode C transponder.

This requirement will hamstring portable ADS-B Out.

[Marc Zeitlin]

So how does the ADS-B performance spec say the altitude is to be derived?

According to AC20-165, it's Baro pressure, although there's some mention of GPS derived altitude as well. It does say this:

Installation Guidance.(1) The barometric altitude used for the ADS-B broadcast must be from the samesource as the barometric altitude used for the ATC transponder Mode C reply, if analtitude-encoding transponder is installed in the aircraft.

Not sure what Skyguard will do about that.

HOWEVER, the AC alludes to, and the RTCA DO-282B seems to indicate that either the Baro or GPS "Height above Ellipsoid" altitudes may be acceptable, so maybe that's all that Skyguard needs to supply. See:

http://adsb.tc.faa.gov/WG5_Meetings/...-282B-FRAC.pdf

But Navworx has a full solution (and at 1/2 the price, apparently - wheee!).

Progress, and fast!

[Marc Zeitlin]

ADS-B Out is required to be integrated to a Pressure Encoder, and it has to be the same Encoder that is feeding the Mode C transponder.

This requirement will hamstring portable ADS-B Out.

Maybe - it says that IF you use pressure altitude, it must be the same as from the Mode C. But as I indicated above, at least a cursory reading of the DO-282B document seems to indicate that maybe the HAE from GPS is also acceptable. Don't know...

[TedK]

I couldn't do a cursory read of the 670 or so pages of the MOPS without my eyes rolling back in my head, but the advisory circular seems pretty clear that Baro Alt is required and should be the same source as used for Mode C.

Why would anyone go thru the trouble of integrating the ADS-B to Baro Alt if they didn't have to?

[Kyle Boatright]

You have touched upon one of the problems with a "portable" ADS-B that could be moved from aircraft-to-aircraft. If someone like Garmin were to make a ADS-B OUT version of their GDL 39, they would need a way for the Broadcast Message Elements to be entered into the device, so that the aircraft N number and base 16 hex code could be transmitted.

I realize it is part of the regulation, but the question is "Why?". There is no legitimate reason VFR aircraft need to be identified by N-number on whatever system(s) the FAA is running.