Airbus FCU technique w/RNAV
 

Regarding RNAV approaches, what are you guys doing


Prior Company, LCC all-Airbus operator (USA). Training department was basically "Airbus factory curriculum"

"Cleared for approach" (APPR is green/active in MCDU by now)

Push APPR pushbutton, arm the approach
Set "bottom altitude" FAF/FAP altitude in altitude window FCU
PUSH altitude knob
Set missed approach at FINAL APP

Current Company, mix of Boeing and Airbus

"Cleared for the approach"

Push APPR pushbutton, arm the approach
Do nothing else
Set missed approach altitude at FINAL APP

Both "work" but....

Thanks

We managed descent until FDP altitude. When FDP waypoints is the « to waypoints » we arm the approach. That’s Airbus SOP by FCOM. But some guys will arm it way earlier and it works just fine. But if too high on profile, I noticed it does some aggressive nose down inputs which can be problematic if you already have flaps.

What does setting the bottom altitude and pushing the button do for you after you arm the approach? And what your current company does works too if you are on vectors for the approach, HDG and ALT till FINAL APP, don't change the altitude window till then.

Setting the FAF altitude on the FCU with altitude constraints on the way will work in principle when:

- flying a full procedure that comes with stepdown altitudes correctly coded in the database,
- flying in DES, not any selected mode.

However, bear in mind that ATC only sees Your FCU altitude and does not know whether or not You are going to keep the higher altitude constraints. There are airports where there is a major separation issue behind those: consider LLBGs RNAV Visual GAVRI 30 or the RNP X where You are to maintain 5000´until REBDO to keep clear of possible go arounds that will climb 4000´and cross below You and also 26 departures.

So I would strongly advise using either selected descent or, at the very least, keeping the FCU altitude synchronised with the currently cleared altitude. In LLBG, this is even a requirement.

When cleared for approach and flying a procedure with many intermediate step altitudes, I simply put the FDP (or FAP) altitude and fly descent mode. I think it’s the easiest and less workload required technique. Then inbound fdp (ie fdp to point) arm approach

Seems like that's the hard way to do it. Why not just verify with the aircraft that they're descending as published on the STAR?

Because only 99% of aircraft will comply. The remaining one will be on its way to a repetition of the Washington collision.

On a STAR and approach with multiple stepdown altitudes that a constant flow of arriving aircraft is fed into, it is simply not feasible to ask every aircraft about their intention to keep its upcoming altitude constraint. This would completely clog up the frequency. Instead, having aircraft show their next intended level off altitude via their FCU window and Mode S transponder is a low-workload method to ensure everyone has the right picture. If some traffic was to proceed to a waypoint with a constraint of 5000´+ while showing a FCU altitude of 2300´ already, questions will be asked - there might even be an automated altitude alert showing up on the controllers screen.

In some airspaces, managed descent is not the best of ideas.

What if…. and just hear me out on this thought… the airspace/ATC is the problem in your Washington scenario and not the aircraft? :ok:

If so, would it not be prudent to operate ones aircraft in a way that minimizes vulnerability to risks offered by the environment?

Neither is correct.

if your aircraft has xLS, the arming conditions for the approach are the same as an iLS, and the missed approach altitude is set like an ILS with F-G/S * & F-LOC*. Procedural descents according to the chart are performed the same as a procedural ILS.

Without xLS, flying the bricks. Approach is armed when the TO waypoint in the FM shows the start of the coded descent, eg shows the start of the 3 degree descent after the waypoint. Should see a descent arrow at this waypoint. Pressing approach prior to this waypoint can result in altitude constraints not being followed.

Missed approach altitude set at FINAL APP.

Prior to pressing APPR, the lowest altitude on the procedure can be placed in the FCU, and DES used, this will ensure constraints are complied with.

We do the second one pretty much. We only set the FAF altitude and manage the descent if we are high and haven't got FINAL APP at the appropriate waypoint.

Fully agree. Plus I believe it is SOP for many operators to always set the next altitude constraint on the FCU regardless of the descent mode in use.

I agree with setting the FCU lowest altitude and with the FDP as to waypoint arm de APP PB.

Few months ago I was looking where I can find that's necessary to put the lowest altitude on the FCU. Why I can't set the IAF or IF as the altitude. Or I'm wrong?

Regards!!