Why do I need to put in my tail number? Isn’t there a 1-to-1 relationship between ICAO 24 bit code and my tail number. Since ICAO 24 bit code is programmed into the ADS-B out device upon installation, it should suffice, no?
In the US, the 24 bit ICAO aircraft ID is related by an alphabetic sorting order to the N number, but for most states, there is no relationship. On the Garmin transponders, you enter either the N number or the ICAO aircraft ID, and the other input is set automatically.The field that contains the N number in alphanumeric coding is called the Flight ID and is your call sign. For air carriers, this is set at pre-flight time by the crew to be the flight number.
I am considering upgrading my old mode C, a Bendix KT-76A, with Bendix ADS-B KT-74. This way I am 2020 compliant, can throw out my old mode-C, yet still can fly international. A UAT solution would not allow me to fly internationally, unless I keep my mode-C around. The KT-74 is much cheaper than the Garmin solutions. I get my whether from a portable solution, such as Stratus 2 hooked up to an iPad Mini. I prefer this, since I don’t want to depend on just one single device and LCD screen for everything.
If you primarily fly in the US, I would not recommend that you do this unless you have an operational need to fly at and above 18000 MSL because all you achieve compliance but do not receive any of the traffic or weather services. With a UAT such as the GDL88, you get both traffic and weather services. If you keep your KT76A, since it is a mode A/C transponder, the UAT solution adds anonymity when you are VFR and not receiving ATC services. A mode S transponder always emits its unique identifier and your N number is always known. With a UAT, there is an anonymous mode that when used generates a “self assigned 24 bit identifier”. A bit is included in the ADS-B broadcast indicates to the GBT that the 24 bit value is self assigned. It is automatically assigned by the UAT unit at the instant the mode is first selected. The value is based on the most significant portions of the latitude and longitude concatenated with the number of seconds since GPS beginning of day and then exclusive or’ed with the actual aircraft ID. This last step assures that two aircraft side by side will get a different self assigned identifier. If you install a mode S transponder and a UAT, anonymous mode is not permitted or you would appear as two targets. With regard to international usage, although I expect other countries to adopt 1090ES because it is the international standard, so far only Australia is mandating its use for IFR. In our hemisphere, Canada does not mandate its use but has adopted the technology and is using it to provide better services for aircraft equipped, but only over the Hudson Bay and only above FL290. Europe has a mandate that will affect aircraft over 250 Kts and more than 5700 KG. For my Bonanza, the only way I will get to 250 Kts is if the wings come off.
However, what I am unclear about is the issue regarding ground determination? I.e. in the case of KT-74, with GNS 430W as an position source, ground determination via GPS input should be good enough, but I read that some add a switch hooked up to the static pitot line to determine speed, or use the landing gear ground safety switch. That seems like unnecessary, and avoidable installation cost.
Even mode S requires ground determination. Garmin does this by various methods including using GS from a GPS. This is frowned on, but not prohibited. For ADS-B, ground mode mostly affects what happens at an airport with surface GBT support. Many aircraft don’t have a weight on wheels that may be used to determine ground status and in the case of the Bonanza line, the squat switch can’t be used for this purpose without extensive rewiring and adding an additional switch. Trig and its variants have adopted using an airspeed switch that is easily installed and costs about $100 plus labor. Labor should not run more than an hour to accomplish this. IMHO, it is an elegant solution that works for most all aircraft types and is in the noise in terms of expense.
Avidyne was showing tail numbers, but only N-reg ones apparently
Presumably because they’re not very interested in the market outside the US…
Others that have an algorithmic mapping include Finland, Turkey, Yugoslavia.
In fairness, algorithmic mapping works for countries with a 15 bit allocation and 3 letter suffixes, and for the US with its 20 bit allocation.
It wouldn’t work for the UK and Germany with an 18 bit allocation and a 4 letter suffix, as encoding all possible registrations would require log2(26^4)=18.8 bits (plus a few codes for gliders which might have numeric registrations). So the UK and Germany were pretty much forced to adopt a database solution.
It wouldn’t work for the UK and Germany with an 18 bit allocation and a 4 letter suffix, as encoding all possible registrations would require log2(26^4)=18.8 bits (plus a few codes for gliders which might have numeric registrations). So the UK and Germany were pretty much forced to adopt a database solution.
Yet they both do. I don’t know the exact algoritme though. Could be that they have limited some combinations in the suffix or something like that. It’s likely based on your calculation that they made some additional rules.
@NCYankee Thank you for your detailed response. Yes, I am flying in the U.S. Due to my proximity to Canada, my solution must work internationally as well.
Regarding UAT versus 1090ES, my rational is the following:
I like the 1090ES solution over UAT because I end up with one less device, because I don’t need to keep my old KT-76A around, that can break and takes panel space. I have a GNS430W, and the display is quite small to display weather and traffic. So I prefer displaying weather and traffic on a high resolution display, such as iPad Mini, using a portable ADS-B IN receiver, such as the stratus 2. I get other UI advantages, such as showing NEXRAD looping, instead of only the last static image. This solution adds redundancy, i.e. in cases such as power loss, LCD screen breakage, etc… The GNS430W becomes the center of everything, which I don’t like. With a stratus 2, I keep most of the functionality of the GNS430W (moving map, weather, traffic, database) completely independent from ship power. Besides that KT74 is half the price of the Garmin transponder.
The lack of an anonymous mode is an issue, which I don’t like, but I’d say for half of my flights I do request ATC services, and I am willing to swallow this disadvantage.
Regarding ground determination, do you know why using GPS GS is frown upon? The GNS430W knows my groundspeed, altitude, the airport I am located at, and the airport altitude. Even if I am at a private strip, too small to be in the GPS database, and ground determination would be wrong, nobody would really care in this case.
As a side note, I am not yet sold on ADS-B installation, and may wait a few more years. I get already weather, and the probability of a mid air collision is too small outside the traffic pattern, where ADS-B traffic would not help much anyways. I calculated the minimum install cost, which is upgrading my KT-76A with a KT-74 at $3700. Too much, for almost no benefit.
Canada states they do not plan to require ADS-B as mandatory and will rely on voluntary adoption for those users who see a benefit. The cost of a GDL88 is within a thousand dollars of a transponder upgrade.
Yet they both do.
Do you have any reference for this?
I browsed G-INFO a bit, and it looks to me more like they went through their database, and just allocated ICAO ID’s sequentially to the “active” aircraft.
Furthermore, you can request a specific tail “number” if you newly register an aircraft in the UK. If there was a fixed algorithmic ICAO ID mapping to registration, then about half of these requests would have to be turned down because they hit an unencodable registration. But that’s not what I heard. It seems like every owner of aCessna in the german registry registers his tail “number” with D replaced by G these days, and from what I heard this was fairly painless.
do you know why using GPS GS is frown upon?
Maybe because if you experience a headwind about as strong as your airspeed, your transponder would suddenly report “on ground”?
Maybe because if you experience a headwind about as strong as your airspeed, your transponder would suddenly report “on ground”?
I assume that this is the reason, but in my opinion this is rather hypothetical. Such a slow airplane won’t be allowed to land at a busy international airport where ground determination matters. It just changes from one set of problems to another. If you use an airspeed switch, you add another mechanical component that can fail (corroded contacts, micro-switch breaks, pitot tube partially clocked).
Canada states they do not plan to require ADS-B as mandatory
I understand, but with a GDL88, I need to keep my old mode C around, whereas with a KT-74, I don’t. So one less old device.
Such a slow airplane won’t be allowed to land at a busy international airport where ground determination matters.
That wouldn’t be a valid assumption in the US, because there is no such prohibition. For instance I believe you can rent a J3 Cub at John Wayne Airport, an international airport where ten scheduled airlines plus FedEx and UPS operate in Class C airspace. I understand on that plane the radio and Mode C transponder are battery powered, minus generator.
If you use an airspeed switch, you add another mechanical component that can fail (corroded contacts, micro-switch breaks, pitot tube partially clocked).
The big plus of the airspeed-static differential switch is that the installer doesn’t need a brain. He just needs a knife to cut the existing tubing, get some crappy plastic stuff from an acquarium shop, and cable-tie it all together. In fact, just like this EASA 21 + EASA145 + well known major-brand dealer 
And if you get the cable tie just right, it will come off in flight 
Whereas to make a connection to the landing gear needs a brain to understand how it is wired, which is why this EASA 21 + EASA 145 installer told me he used the pressure switch.
Also, on a fixed gear plane you can’t use the gear.
The GPS GS switching fell out of favour in Europe a few years ago when EASA made this dodgy ruling which one UK avionics shop (EASA 21 + EASA 145 too but not the same one) said in a posting that they “had to” rip out the connection on a large number of aircraft because it made them illegal. Garmin later brought out new firmware which ignored the GS input for the purposes of radiating the data. Also the GTX330 never worked with King GPSs for this purpose, despite Garmin showing the connection in their IM. They appear to have fixed that only recently, about 10 years later.
ADS-B trials in UK GA aircraft
Anyone participating ?
That looks like a late 80’s TB model.
From IAOPA newsletter:
“See and Avoid” equipment trial planned
http://www.iaopa.eu/contentServlet/iaopa-enews-february-2015#More3
