Originally Posted by
vilas
mi68guel
The answer by airbus to your company's strange question is equally strange. First your company's question: This is the question from my company to Airbus (customer email):
"Is it legal and permissible under Airbus recommendations, to have active final approach mode prior to the FAF without proper FMS coding i.e. a defined FPA"
The answer should be it is not possible. Because FINAL APP can only be armed before FAF and only becomes active after FAF or VIP. Perhaps your company meant is it OK to arm the approach. Now the second part of the question, your company wants to know if it's OK to do managed approach without proper FMS coding and again the answer should have been "Hell NO" because before embarking on managed approach it is mandatory to check proper lateral and vertical profile in the MCDU with approach chart and FPA is one of them. FCTM explains all the points that need to be checked. When armed FINALAPP mode will not become active unless you are on track and at FAF altitude before FAF or VIP as it is called.
I really like this reply!
The problem is in the question. They asked something that's not possible..."to have
active final approach mode prior to the FAF". This is not clear, because we can't understand if they mean "armed"( FINAL blue) or "engaged" (FINAL APP green). If they mean armed it's the normal situation, but if "active"means engaged, then we'll have to writte down this defect on the techlog and probably to fill an ASR.
So If we want a proper answer from AIRBUS, the question should have been more precise and using FCOM terms (armed and engaged) and that's the reason I consider they didn't fully understand the question but they tried to help and replied generic things.
I also don't understand from the question where it says "active final apch mode prior to the FAF without proper FMS coding, i.e. a defined FPA". What matters is to check max 0.1 degree of difference between MCDU and the chartered
final vertical path.
Before the FAF when you arm the apch, only lateral mode is engaged: vertical mode is still under FMS that should comply with ALT CSTR's if descend is managed .So there's nothing illegal on it, the only difference is that we are arming FINAL (in blue) to have it ready before the FAF .At FAF in FINAL APP mode the lateral separation is still under NAV control (RNP 0.3 for us) and vertical guidance is different, the primary means of obstacle clearance is then provided by the VNAV system rather than the altimeter, and adherence to the vertical flight path within reasonable tolerance is required. .So this FINAL APCH mode needs an augmented GNSS system (ABAS in A320 and A330) with Baro-VNAV that uses barometric altitude information from the aircraft's pitot-static system and air data computer to compute vertical guidance for the pilot (for RNAV (GNSS) with LNAV/VNAV minima).
Conclusion: if we armed the approach before FAF at intermediate APCH the lateral and vertical profile is gonna be the same as if we wait until reaching the FAF altitude.In the first case, if something goes wrong, we are following official documentation (FCOM, FCTM, Instructor's media..) but in the second case we are relying on an email that has no legal validity (I'm not a lawyer, but I would be ashamed to defend myself against investigators using an email as SOP reference)