VAPP computation: A320 Abnormal procedure
 

Hello everyone,

During an abnormal procedure that would require a landing in config 3, do I have to add the delta VREF before or after having selected config 3 on the MCDU?

In other words, is the delta VREF added to VLS config 3 or VLS or config Full?

At my company, they want us to add the delta VREF to VLS Config FULL and even after that, they leave config FULL on the PERF page even though the landing will be in Config 3.

They say that it does not change anything.

Lastly, am I mistaken in thinking that if one lands in flap 3, with config FULL on the MCDU, the approach speed will be F speed and not VAPP?
Will I even get GS mini in that case?

I hope I'm clear enough.

If you guys could provide FCOM references with your replies, it would be great.
Thanks in advance

Vref IS Vls(full). And exactly as the tables say, the additive is to Vref, i.e. to Vls (full).

Your company is correct in A) exactly as per Airbus procedure.

Your company is technically correct in B) as well (it does not change a thing) however, the Airbus procedure is to select F3 afterwards in the MCDU. I believe that is for consistency.
As a general rule, you do not want to have incorrect information displayed willingly anywhere on the flightdeck.

Regards, references to follow later.

Thank you for the reply.
So this is true even regarding F speed? Airplane will slow to VAPP? and not stay at F speed?

Vapp determination with failure: (from the QRH PER-A 5/6)

VAPP = VREF + DELTA REF + APPR COR

Just get the Vref value (according to your weight) from the Vref table.
You have only 2 options CG aft/forward.

To answer your question, DELTA REF is add to VLS CONF FULL. As shown on the table.

However, I don't understand why they want you to leave CONF FULL on the PERF MCDU?

They don't insist on leaving Conf Full but rather saying that it doesnt make a difference whether Perf page is set on Config 3 or Full.

To answer your first question refer FCTM PR-NP-SOP-160 p15/30. It describes how VREF = VLS in CONF FULL. This why abnormal landing VAPP computations start with VLS conf full add delta VREF and then we change the MCDU back to CONF 3. ( however I don’t think this does anything other than changing the VLS value on the PERF APP page. VAPP can’t change as you manually entered it.)

The computers take the landing configuration from the GPWS LANDING FLAP SELECTION. So providing it is set to CONF 3 the GS Mini should be available ( F Speed disappears from speed tape on selection of landing CONF ) and Landing memo will correctly show CONF 3.

Hi saviboy,
As I understand it, Auto Thrust won't fly any slower than F speed if you leave the PERF MCDU set to CONF Full. However, since you've made a +ve correction to VAPP, then your new VAPP is usually > F speed so you won't notice the difference.

GS mini is active throughout the approach. See FCOM DSC-22_30-90 Speed Mode in Approach Phase.

I always reset the MCDU Landing CONF to 3 AFTER I'd applied the DELTA REF - just to keep it simple (for me).

Some of the MCDU entries serve as reminders. Why do you enter OEI acceleration altitude? That also doesn't change anything. The PF keeps PERF page on approach. Is there any reason to keep erroneous information on it? Unless you are trying to confuse your self.

Thanks for all the replies everyone. Much appreciated.

Gentlemen above have differing opinions about how the flight guidance understands what is the final approach speed: OVHD or MCDU? It is part of the OP's query too.

I am trying to find a reference, and not being very successful with it.

The OVHD panel pb LDG FLAP 3 is part of the GPWS panelNeither has the MCDU page description any clues

And no luck finding anything in
. DSC AUTOFLIGHT - A/THR
. DSC AUTOFLIGHT - Speeds Definition
. DSC F/CTL

However PRO-NOR-SOP-16-A DESCENT PREPARATION: PERF APPR says "Check or modify the landing configuration. Always select the landing configuration on the PERF APP page: ..."

I went to FCTM: nothing found. QRH: same result. :sad:

Overhead (GPWS) is to reconfigure the ECAM landing memo and GPWS.
MCDU flaps3 is for the A/THR to know that Vapp is for F3 and to allow possible flight below F speed in managed speed. (GS mini will work regardless btw)

When landing with flap lever less than 3 (gpws flap mode off) don’t worry about changing the config in the MCDU as you will fly neither.

We had a sim fault the other day for a slats fault. The autothrust is off, there is no ice accretion and the winds are calm. Therefore, Vapp equals Vls. But 5 knots was added anyways. The company requirements for stable approach are not below Vls, so we added a margin.