A320: Altitude constraints during go-around

[J.L.Seagull]

FCOM DSC-22_30-70-20 says: "The flight crew can arm the CLB mode during the takeoff, go-around, climb, and cruise phases and engage it during the climb and cruise phases."

It elaborates further:

"The CLB mode is armed:
‐ In flight, when the climb or go-around phase is active, and the following conditions are met:
• The lateral NAV mode is engaged
• The FCU selected altitude is above the aircraft’s present altitude and the aircraft captures orflies an altitude constraint."

And yet further:

"The CLB mode can be engaged, if the following conditions are all met:
‐ The selected FCU level is above the present aircraft level
‐ The descent, approach, or go-around phase is not active
CLB mode automatically engages when the aircraft reaches ACC ALT, or sequences a waypoint withan altitude constraint while the CLB mode is armed."

There seems to be a contradiction there. When the GO AROUND phase is active, CLB mode can be armed, but not engaged??? And in the very next sentence: "CLB mode automatically engages when passing...." Am I missing something?

So, my mental picture goes something like this:

I'm on final approach, on the ILS (FMA showing SPEED, G/S, LOC), 7000ft set as the missed approach altitude in the FCU window. However, there is a constraint programmed in the FMS. for example 3000ft till reaching 8DME, then turn and climb.. etc. etc. ACC ALT is set at 1500 AGL. (Assume airport elev = 0ft)


1) I'm at 400ft AGL, and I perform a go-around.i.e. Thrust levers to TOGA.
2) I expect to see MAN TOGA, SRS, GA TRK on the FMA
3) I manage HDG and see NAV on the FMA
4) At ACC altitude, the aircraft should no longer be in SRS mode.

Bringing the thrust levers back to climb should engage A/THR and THR CLB mode, with GREEN DOT as the speed target.
Laterally, since NAV is engaged, the airfract should follow the missed approach procedure.
But I'm not sure what to expect next for vertical guidance. According to the FCOM, CLB mode can be armed, but not engaged in the GO AROUND phase. And yet it also says that passing ACC altitude CLB will enagage! HUH???

So I thought about the GO AROUND phase itself. FCOM DSC-22_20-30-20-05 states the conditions for activation of the next phase. From GO AROUND:

1. To Approach: Manual activation of the approach phase, or
2. To Climb: Above acceleration altitude by
‐ Selecting ALTN, or
‐ inserting NEW DEST

This infers that the aircraft will remain in GO AROUND phase unless someone manually inserts something into the MCDU.

Long story short... will it or wont it??? i.e. will CLB mode engage? and will it respect any altitude constraints programmed into the FMS?

[sonicbum]

Hi JL,

in your scenario passing your acceleration altitude the vertical mode will be OP CLB. Climb mode will not engage during the go around phase as the FM makes no predictions. The reasons it makes no predictions is that the system is waiting for you to tell him what is your plan after the go around, either another approach (activate approach phase) or divert (enable ALTN / new dest). It is the same concept of when you are flying in heading, you don't get the CLB or DES as the system does not know where you want to go.

Hope that helps:ok:

[Winnerhofer]

Hit EXPED!

[J.L.Seagull]

Thanks Sonic.

Exactly what I assumed... Just wasn't sure, coz I've never had to do it so far.

Seems like an anomaly on Airbus' part. There are so many airports out there that have constrained climb procedures as part of the missed approach. If you're in NAV, I can't see why the aircraft can't respect the constraints automatically.

Maybe they were worried about single engine go around performance. But then again, all that is required is to pull HDG and fly the engine out procedure manually.

Oh well.. As long as I know what to expect, it's fine.

[hikoushi]

Just as long as you remember (A330), when you get to the point in your approach where your SOP has you setting a missed approach altitude (at the 1000 foot call on final for us), set the FIRST "at" or "at or below" constraint altitude in the procedure in the FCU. So if you have a complex missed approach procedure that says "cross XXXXX at or below 2000, then continue climb to 5000 direct YYYY", set 2000 in the FCU. Then you will be okay.

[deefer dog]

It wasn't that many years ago that us old farts were flying "overshoots," as they were known then, on something we used to call "raw data."

Reading above variety of explanations and multi button pushing exercise makes me think that they were a lot easier back then.....handling pilot calls gear up and clean up, then his mate tells him how high at what place, and what "radial" (old fashioned things we used to follow) to turn onto.

CRM (not that it was known by that term at the time) and airmanship is wot were needed, not degrees in managing a computer. Less hands flying around the cockpit, more "hand flying" and none of that "what's it doing now."