No matter how much you computerize and automate and digitize via pressure-sensing transducers, the pneumatically derived values of pitot pressure (dynamic plus static) come from the same sources. However, courtesy of automation, the engineers are free to determine whether or not they should integrate the port and starboard digitized values and compute an ongoing average value or also incorporate (and integrate) the "pitot-derived static" in order to "iron out" the minor errors at different speeds and attitudes/altitudes related to the static sources (aka position error correction).
As you'll no doubt be aware, the source of the speed display on an ASI is the result of "balancing" (or deducting) the "static source derived" static pressure against that (perhaps slightly different) static pressure that's part of the dynamic input to the pitot heads. That's why, when water in static lines freezes, the ASI will wind back to zero in a climb. It only takes about 2000ft in a 210kt climb as the pitot-derived component of static is overcome by the much greater trapped static line pressure. I've seen that on a number of occasions due to aircraft being parked in rain without static port bungs in place and the "sucked in" rain-water freezing as you pass freezing level in the climb (altimeter stops, VSI reads zero). You're then in POWER + ATTITUDE = PERFORMANCE country. If you're feeling destructive, you can depressurize and smash the glass face of the VSI to get a source of unfrozen static pressure and restore speed display, altimeters and VSI.
When you take into account that there are at least two (sometimes three) pitot heads (e.g. the A330/A340) and multiple static ports, then the engineers are "spoilt for choice" when it comes to sourcing and integrating their data flows to the ADIRU's.
It's never done as simply as you may think. Keep in mind also that normally there will be little difference between port and starboard sources (airplanes being symmetric and normally flying symmetrically). However an inadvertent spin entry from a coffin corner loss of control situation may change that port/starboard equivalence in both pitot and static - and be capable of providing the sort of speed disagreements between ADIRU's that would generate the messages sent by ACARS in the final 4 minute plummet from altitude in a spin/spiral.
Hello,
I was reading your post
1582 and
noticed this term:
"pitot derived static"
Am I to understand that it is possible to extract static pressure from the pitot line?
I'm a curious glider pilot.
Cheers,