This is news to me... i work for an airline with lots of Airbus Airplanes.
QRH page 123, amended 01, Oct. 16states:
All ADR Off: "BUSS equipped aircraft when require by the ECAM NAV ADR 1+2+3 FAULT procedure."
1. SPD......................................................... .....................FLY THE GREEN
2. MODE SEL......................................................... ..........MAN
3. MAN V/S CTL......................................................... ......AS REQRD
for aprroach
4. SPD......................................................... ......................FLY THE GREEN
5. FOR LNG......................................................... ..............USE FLAPS 3
6. GPWS LDG FLAP 3.........................................................ON
7. landing distance procedures apply
8. APPR SPD......................................................... .............FLY THE BUG
it don't say nuthin about descending to FL 250???
Zaphod, I suspect that's because you are looking at only the ALL ADR OFF situation. Look at the Unreliable Airspeed: It still retains the FL250 caveat.
Lantirn:
My understanding was that FL250 was chosen for certification for the Unreliable Airspeed situation because "most" incidents were caused by icing of probes and most cases this was resolved fairly quickly once probe heat (and maybe descent) overcame the ice and so normal indications would return and could be used However if airspeed was still unreliable below FL250 then issue was most likely not caused by ice (maybe damage) and hence use of BUSS thereafter. One ADR is retained above FL250 if possible for stall warning. Additionally I understand that Airbus were planning certify BUSS use at all altitudes and perhaps they have now but the unreliable airspeed procedure still retains FL250 as they would like you to have normal airspeed indications if at all possible rather than reverting to BUSS immediately.
I also work for an airline with lots of Airbus types.