Originally Posted by jabberwok
It's irrelevant. All transmitted heights are SPS regardless of actual altimeter setting. TCAS is therefore correctly determining the difference between relative altitudes even though these values are otherwise meaningless below TA.
In the cold light of morning, yes I can see clearly now
Blame it on a late night beer
- and brain stuck in a wee loop.
Of course, what I was confusing it with is when someone sets the wrong pressure setting and my radar display then shows up for example FL064 instead of FL070 - the error is in the input, but the height readout is still correct (based on 1013mb) .....
..... ASSUMING THE MODE C IS WORKING PROPERLY ...... (which is still an unanswered point)