Fri Jul 05, 2019 9:08 am
#1703993
I've spun this off from the infingements thread to keep the technical discussion (that I hope will ensue) can be kept separate from the "debate" in the other thread. That way this thread can be linked when this question arises again... it surely will.
One of my fears as an aeroplane renter is that I could be flying along close to the vertical limit of some airspace and a combination of a moment's inattention coupled with a transponder encoder that is reading high but within allowable limits, could deem me a criminal. For example, Coventry's circuit is 1000' with an elevation of 267' - that's only 233' below Birmingham's Class D - I'm sure there are plenty of other examples.
So.... AIUI, some transponders have built in encoders - presumably connected to the static system. Others have a separate encoder (also connected to the static system.)
The software in the encoder works out a FL and sends it out in response to a secondary radar (or TCAS) interrogation.
That FL appears on the ATC radar screen.
So where are the potential sources of inaccuracy in that? I've seen it said that +/- 200' is acceptable from a transponder POV. Is that written down anywhere?
If I'm at 1250' Alt. Would the encoder send FL12 or FL13? What about 1275'?
Is there any processing that is done at the ATC end where error could be introduced?
I know that I could google and spend an hour or more locating and collating different threads, but there's bound to be someone here who just knows! Thanks to them and anyone else who can add to my knowledge (it's not hard)
One of my fears as an aeroplane renter is that I could be flying along close to the vertical limit of some airspace and a combination of a moment's inattention coupled with a transponder encoder that is reading high but within allowable limits, could deem me a criminal. For example, Coventry's circuit is 1000' with an elevation of 267' - that's only 233' below Birmingham's Class D - I'm sure there are plenty of other examples.
So.... AIUI, some transponders have built in encoders - presumably connected to the static system. Others have a separate encoder (also connected to the static system.)
The software in the encoder works out a FL and sends it out in response to a secondary radar (or TCAS) interrogation.
That FL appears on the ATC radar screen.
So where are the potential sources of inaccuracy in that? I've seen it said that +/- 200' is acceptable from a transponder POV. Is that written down anywhere?
If I'm at 1250' Alt. Would the encoder send FL12 or FL13? What about 1275'?
Is there any processing that is done at the ATC end where error could be introduced?
I know that I could google and spend an hour or more locating and collating different threads, but there's bound to be someone here who just knows! Thanks to them and anyone else who can add to my knowledge (it's not hard)
Paul
The forum seems to have stopped logging me out at random intervals. Perhaps they like me after all? (Thanks for fixing it) Our pleasure!
The forum seems to have stopped logging me out at random intervals. Perhaps they like me after all? (Thanks for fixing it) Our pleasure!