Can you show that?
Nope, the reason I said “it appears” to be the case, with two question marks added (??) was to indicate that while the link I’ve already provided is fairly clear in stating that Mexican airspace over 10,000 ft is Class E, I recognize that like any similar article it may be incorrect – based on long experience and physical proximity, I know anything in Mexico tends to be poorly documented and unclear. I have no time nor interest to pursue it further right now, but would welcome any clarification. Maybe PM if you learn anything, to keep it off EuroGA.
In the meantime I’ll mentally file what I’ve learned for future reference, and maybe research it further when my plane has 12 inch N-numbers and could thereby fly to Mexico.
I’d like to fly to Mulege BCS (MX76) and to Alamos Sonora (MM45) at some point, I could make it to either non-stop from the ports of entry at San Felipe or Rocky Point (Puerto Penasco) so what was more interesting to me personally is the link’s more clearly stated requirement for Mode S based ADS-B on the Mexican “coast” above 3,000 ft, because I know the flights I might make to Mexico are likely to follow the shoreline. Even that is unclear because I’m not sure there are any current Mexican charts that would clarify whether the requirement includes the Gulf of California shoreline or just e.g. the Pacific coast shoreline to the west. Welcome to Mexico, where rules are created by one group, enforced by another and documented nowhere.
LeSving wrote:
I know too little about the details, but mathematically I don’t see a problem. The solution is two points, but you don’t know who is who. If two signals arrives at one sensor at the exact same time, then perhaps there is a problem? However, the requirement is Mode A and Mode C. That is, you have to enter a code, and the responder has to be triggered.
That IS the problem – they both return 7000 in Mode-C at approximately the same time. In Mode-S it is the same 7000 times two plus each return the individual HEX ID. And yes, ADS-B is great as that does not require an interrogator – it just broadcasts it all the time…
Silvaire wrote:
I had a moment to take a look at this mostly off topic issue today, and it appears that Mexican airspace between 10,000 and 18,000 feet is all Class E
Can you show that? I don’t see anything but G below 19500 with some exceptions for Class D airspace. Please provide a reference from a Map or AIP.
arj1 wrote:
If you don’t know which one is which, then how would you do the triangulation, aka MLAT?
I know too little about the details, but mathematically I don’t see a problem. The solution is two points, but you don’t know who is who. If two signals arrives at one sensor at the exact same time, then perhaps there is a problem? However, the requirement is Mode A and Mode C. That is, you have to enter a code, and the responder has to be triggered.
In a Mode S/ADS-B environment, the triggering is not necessary. The WAM/MLAT can be 100% passive. This is not possible for Mode A/C, and interrogators are needed.
An additional benefit is that an MLAT/WAM system also can/will calculate altitude, and will do this with an accuracy of about 10-25 feet. Even though Mode C is only 100 feet, when used in a WAM network, the accuracy is still up to 10 feet, and is independent of the transponder in the aircraft (which could be way off). This accuracy requires GPS clock synchronization of all the receivers, which could be a bad thing if GPS is jammed. In those cases it would have to rely on the altitude reported by the transponder in the aircraft.
Clearly ADS-B + WAM is the best of all worlds here. It’s the “final solution” for the foreseeable future (as we know it). Mode S is more of a stop gap for poor Mode C performance (due to poor radar performance), and had perhaps a place 30-40 years ago? But today?
I haven’t found any usage of class E in Mexico. They use D and G, but D does not require ADS-B Out. There is a mode C veil of sorts around Mexico City. Other than that is seems that throughout Mexico, the only airspace that is ADS-B Out is A which is above 19,500, so it seems to me the mandate does not affect UAT because none of the airspace outside of Mexico City seems to require it. They may add more airspace in the future or designate some E airspace areas, but not currently. Do you know of any areas that use E or that will end up requiring ADS-B Out?
I had a moment to take a look at this mostly off topic issue today, and it appears that Mexican airspace between 10,000 and 18,000 feet is all Class E (??) and more clearly all airspace within 12 nm of the coast and over 3000 ft requires (Mode S based) 1090 ADS-B OUT and UAT isn’t compliant. Reference here
I would think the Mode S and ADS-B requirement for shoreline surveillance would be an issue for many pilots and planes in that navigating to many places in Mexico means following the shoreline for a couple of hundred miles and then landing at an airport near the shoreline. Not unlike e.g. Croatia, ‘everywhere’ interesting is near the shoreline. Of course you can do it at 2500 ft if you like but that might mean crossing several Class D airports, which is a hassle given that you are unlikely to be talking to ATC otherwise.
LeSving wrote:
arj1 wrote: Mode-A/C got no way of determining which one is whichADS-B has. But why is it important to know which is which?
See A_A’s post re: ADS-B & 1967 below.
Why important? Sorry, don’t understand your question.
You have two signal coming to a station from two a/c both squawking 7000.
If you don’t know which one is which, then how would you do the triangulation, aka MLAT?
Peter wrote:
So, yeah, somebody identified a tech issue in 1983 but nowhere does it say that this turned out to be a real problem.
You didn’t read properly. The “tech issues” were identified already in 1967 and the FAA commissioned the development of what eventually became mode S in 1970.
The issues were not theoretical. A US Department of Transportation committee wrote, around 1970, that “After examining the existing system, the committee determined that ATCRBS as it stood was too limited to handle the predicted increases in traffic. It lacked accuracy and reliability of position data and had limited capabilities. The frequencies they used were overloaded, which resulted in data loss and garbling. Garbling occurred when there were timing conflicts between two planes replying to different interrogators, when planes within a certain range replied to the same interrogator and their signals overlapped, or when multipath reflections occurred that distorted the signals.” Source.
I repeat: In hindsight, it would have been better to go for ADS-B straightaway, but you could hardly fault people for not realising that in the 1970’s.
if you have two a/c with 7000 sending ADS-B out, Mode-A/C got no way of determining which one is which.
ADS-B provides the tail number of the aircraft to ATC in either 1090 Mode S or UAT Mode C form, unless (available in UAT only) the pilot has selected autonomous mode, which in the US (where UAT is deployed) is not authorized when under ATC control – something which like Mode S and ADS-B itself is optional in all or most US airspace for VFR traffic.
arj1 wrote:
Mode-A/C got no way of determining which one is which
ADS-B has. But why is it important to know which is which?
LeSving wrote:
Both Norway and Finland has finished transforming their airspaces to almost 100% cover of ADS-B/WAM. With radar it was 20-30% perhaps at lower altitudes. Mode S transponders doesn’t do any harm in this system I guess, but offers no real benefits either as far as I can see. None of the benefits that ADS-B would offer.
I’m afraid it does – if you have two a/c with 7000 sending ADS-B out, Mode-A/C got no way of determining which one is which.
You need some Hex ID, which Mode-S provides.
Although I have to say, I was impressed by ADS-B+MLAT/WAM precision, comparing to radar.
