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WhiteKnight
27th Feb 2011, 15:02
Hello,

i just got a question regarding Vapp for an unreliable airspeed event in an
A320.

According the QRH there is one line which says the "APP SPD" is VLS +10 with LDG CONF 3.
If you look in the table for LDG CONF/APPR SPD/ LDG DIST on DRY RUNWAYS for Unreliable Speed it gives you a "delta" VREF of 16.

My Question is now, which value du you enter in the MCDU as your Vapp.

Letīs say your flight plan is sequenced you see a VLS of 115 on the MCDU.

VAPP = VREF+ "delta"VREF+ APPR COR

Is my VREF now: VLS(115)+10?

and VAPP = 115+10+16+APP COR?

Any advise of how to handle the extra 10 knots given in the QRH would be great. Thank you

shortfuel
27th Feb 2011, 15:59
The unreliable speed indication QRH procedure gives pitch/thrust settings in order to fly at Vls CONF 3 + 10kts.

If you want to insert your computed Vapp as a reference in the PERF page then, it is Vref (always = Vls CONF Full) + 16 + appr cor.

In your example, 115 (empty a/c!) +16+ third Headwind (if any).

Having said that...in an unreliable speed situation, you do not rely on speed indication anymore so fly pitch/thrust/config, should be more than enough!

The only use you could make of a computed Vapp is to compare it with your IR ground speed (corrected for wind and altitude) to check you are more or less flying at the correct speed range. It would be a sort of memo nothing more.

Microburst2002
27th Feb 2011, 16:54
In an all ADR wrong or failed scenario, What is the point in inserting any VAPP in the MCDU?
All I need to know from the LDG DIST PROC is exactly that: the distance factor. I will fly the G/S with the target pitch as per the QRH table, ignoring any indication in the PDF speed tape (actually I would recommend that the pilot flying has its ADR switched OFF so the tape shows only the red SPD flag).

However there is a discrepancy between the 10 Kt in the QRH procedure when all ADRs are wrong and the 16 kt of the LDG DIST PROC in the QRH.

Why?

Airbus is always messin this section of the QRH. They revise it every six months!

shortfuel
27th Feb 2011, 17:18
There is no discrepancy gents...

Vref+16 is about Vls conf 3+10. This is consistent.