AlexTB20 wrote:
the TRX-1500A GPS signal is Source Integrity level 0 (SIL=0)So it won’t show on any certified TAS/TCAS equipment. I can leave the transponder connected to the existing GNS530, as it makes no difference.
To clarify, the SIL level affects being shown on ADS-B in devices. The small number of airliners with ADS-B in will not be able to see you and nor will ATC (currently) offer any sort of ADS-B services to you – not that they offer to anyone right now. Your mode-S transponder will still show on TAS and TCAS systems. These essentially have nothing to do with ADS-B at present.
Peter wrote:
For a start, supposedly, displaying anything below SIL=3 on certified avionics is illegal.
I believe that SIL not equal to zero allows certified avionics to display target. SIL equal to 3 is required in order for the position data to be used by ATC.
SIL is a probability that the broadcast containment radius may be exceeded without anyone knowing. So 0 means that it is unknown or unknowable. SIL of 1 is 1 in 1000 flight hours, SIL equal to 2 is one in 100000 flight hours, and SIL equal to 3 is one in 10,000,000 flight hours.
Your mode-S transponder will still show on TAS and TCAS systems
What is really showing up on TAS and TCAS systems is one’s Mode C transponder.
The extra Mode S data is not evidently used by any GA active-TAS product – except a long-obsolete Avidyne MFD which displayed tail numbers of N-reg targets, when fed from a TAS6xx TAS box.
JasonC wrote:
any sort of ADS-B services to you – not that they offer to anyone right now
I got left wondering yesterday, after amsterdam gave us an absolute heading to fly (vs relative heading e.g. turn 15 degress right), how did they have the information of our present heading (we hadn’t been on radar heading either).
Is it from ADS-B, another system, or would they just have guessed our heading given that we were pretty much directly into the wind (thus had very little drift)
Well, it’s actually simpler to give an absolute heading, as you only need the current position for that, as opposed to a relative one, where you need to know the current heading as well.
AlexTB20 wrote:
Well, it’s actually simpler to give an absolute heading, as you only need the current position for that, as opposed to a relative one, where you need to know the current heading as well.
When ATC gives you a heading it’s presumably to alter your trajectory (or to just put you under radar vectors so you don’t change your trajectory when you hit your next waypoint).
Whey they want a small adjustment of your trajectory, say 15 degress, how can they do so optimally (without giving you an excessive correction) if they don’t know the heading you are flying currently?
Are we criss crossed on the absolute vs relative?
For me absolute is they tell you “Fly heading 215”. Relative is “Turn right 15 degress”. Unless they know your starting heading, they won’t actually know what the effect of an absolute heading instruction will be.
I must be too tired, or oxygen deprived :) Now matter how many times I read it, I still think absolute will only need position and relative needs current heading also.
Maybe someone else care to join with an opinion?
ATC in the US assigns headings to fly on vectors and does not know my precise heading. They most likely have issued a previous heading to you or another aircraft and as long as your compliance with the heading gets you going within +/- 10 degrees of where they want you to be tracking, that will probably be good enough. If it isn’t, they will usually adjust your assigned heading. If you are totally off the track they wan’t, you may get a “say heading” request to figure out what is going on. It is possible for ADS-B to provide your heading if it is available in the data provided to the ADS-B Out system, but it is not a mandated item.
Noe wrote:
Is it from ADS-B, another system, or would they just have guessed our heading given that we were pretty much directly into the wind (thus had very little drift)
They will often just match your heading to that of an aircraft they are trying to separate your from.
Sometimes air traffic will ask your heading when they ask you to follow present heading. Changes are then made from that. Sometimes they see you converging and guess the right adjustment and ask you to do it.
I’d have to go in the books but since mode-s (ehs) at least on the self loading freighters atc can see everything dialed into the mcp (mode control panel) and much more. No more cheating on the speed on approach.
Maybe the citation is the same Jason?
