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I read in the Airbus A320 FCTM (p349), normal procedures descent section:

The flight crew can insert a lower VAPP in the MCDU PERF APPR, down to VLS, if landing is performed without A/THR, without wind and no ice accretion.

You have no margin against a stall condition. Why is that possible to decrease VAPP till VLS?

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... if landing is performed without A/THR...

Then theoretically you don't need the VAPP [setting] and should fly a bit faster, it's only a speed bug in this situation.

... without wind...

Even if the METAR is reporting an average of 0 knots, there is always a breeze here and there.

... no margin against a stall...

You have a 23% margin. VLS is 1.23 VS at 1G (check FCOM 4.03.20). So if the stall is at 120 knots, then VLS is 148 knots.

Note:

VAPP should be at least VLS +5 kt.

So VAPP even becomes 153 knots, 33 knots above stall. Plus the A320 by design has anti-stall measures if the flight laws are not degraded.

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