Originally Posted by Bearfoil
Ahhh.... So the a/c flies for ten seconds on one read? Is that the ten second interval I suss @ 2:10:16 "so.....we've lost the speeds, Alternate Law?" (PNF?).
Am I close? If the a/c was ten seconds into flight calculated on one airspeed, what could the PF/PNF be seeing when the reads update?
NO again, you are far!
Autopilot disengages and ALT2 is triggered immediately without waiting for 10 seconds confirmation.
CAS_System is used by aircraft avionics systems (autoflight, flight controls); it is NOT displayed on PFDs.
* Captain's PFD: CAS1 = ADR1 = real value displayed if > 30 kt.
* F/O's PFD: CAS2 = ADR2 = real value displayed if > 30 kt.
* Standby: CAS3 = ADR3 (not displayed, in replacement for CAS1 or 2)
* ISIS: CAS3bis = same probes as ADR3, but analogical values (no ADMs computation) = real value displayed if > 30 kt.
Consequently, if Captain's Probe-Pitot becomes clogged and ADR1 airspeed drops immediately from 275 kt to 60 kt, Captain's PFD will actually display 60 kt even if the system CAS will retain the last valid value of 275 kt for monitoring all ADRs output during 10 seconds following the fall of ADR1. Same for F/O, ISIS with their respective ADRs.
That's how RTLU would retain the last valid airspeed if the 10 seconds airspeed test failed but, if the test is passed, it will function normally.