TCAS warnings not affected.
TCAS procedures strictly prescribe NOT to use the display for avoidance manoeuvres.
ABV/BLW extends the DISPLAY range from 2000 to 6-8000 feet in the chosen direction, the opposite one remains at 2000.
The older units still display targets ONLY +/- 2000 anyway.
The deciding fact is actually the words DURING TAXI = MEL restrictions do not apply, thus:
A) Commander understands the functionality of the system is not degraded (see above) in any way and proceeds with the flight.
B) He reports the status of the switch to MCC at some stage,
C) where the experts decide what happens before the next leg. In accordance with their manuals and Quality Assurance protocols.
Last edited by FlightDetent; 11th Jul 2018 at 18:51.