changing speeds on PERF page: Airbus

[Jumeirah James]

I need clarification please Gents/Ladies:

I was under the impression that if you had Vls showing on your speed tape on your PFD, you didn't need to change the VRef speed on the PERF page in a non standard config (e.g. Flaps or slats stuck). I thought you only have to insert the QRH VRef addition to VApp if VLS was not shown. I thought Vls is related to the ACTUAL F+Slat position, so inputting anything in the VLS PERF page was not required.

I have now been told that irrespective, you have to change VLS to include Vref apph increment.

Please help :ugh:

[tom775257]

With reference to the A320:

To answer one question: Correct, VLS on the PFD is computed from actual slat/flap position, whereas Vmax/VFE next are computed from flap lever position.

You can't adjust VLS on the perf approach page, you can only adjust Vapp.
If you have a failure which calls for a Delta Vref (in my case from 2.32 QRH) you should obviously apply this and adjust the Vapp accordingly. Whether VLS is shown or not on the speedtape has nothing to do with anything as far as I know - if you have a delta Vref, apply the delta Vref.

Cheers

[A330AV8R]

Hi James

ok here goes with reference to the A330 , some failures typically slat and flap lead to an increase in VLS in this case the VLS desplayed on the PFD takes into account the actual configuration , in some other cases you have to fly the aircraft at a speed higher than VLS simply to better its handling characteristics at that point , this is your Delta VLS provided by ECAM , this speed increment is to be added to the VLS displayed on your PFD when landing conf is reached . . . . .

again QRH 2.40 as you know is where you get the formula to find the Vapp .

hope this helps

:ok:

[Bruce Waddington]

JJ,

When in a failure situation that requires an increase in airspeed the first step is to complete the ECAM and then reference the QRH to determine the Flap setting for landing and speed increment to be applied to VLS (VLS is sometimes called VREF.)

In all failure cases requiring an increase to VLS the increase is applied to the Flap FULL VLS found on the Perf page. Therefore, apply the VLS increase to the VLS found on the Perf page and enter it on the Perf page as the new VAPP.

Remember that you can never manually change the VLS, only the VAPP.

best regards,

Bruce Waddington

[Jumeirah James]

Thanks very much for taking to all for the time out to reply. It's clearer now :ok:

[Chris Scott]

It's been 6 years (so check this out in your FCOM) but, as I recall, another reason for updating VAPP on the FMGC PERF page is to ensure that you retain GS-MINI (minimum-ground-speed protection) on the approach.

For the same reason, always enter a realistic surface W/V as well. For example, if there is a headwind on the runway of 20kts, gusting 30, do not be tempted to enter 25 kts, instead of 20. If you do, the minimum ground speed calculated by the FMGC will be nearly 5 kts lower, and - when the stronger headwind on the approach dies away to 20 kts as you cross the threshold - the resulting IAS will be lower than you are expecting.

[I am assuming that GS-MINI is still a feature of all A320s/330s/340s ?]

Enjoy flying your Porsche office,

Chris

[IFLY_INDIGO]

VLS displayed by the FMGS is calculated by FMGS assuming the expected landing weight and selected config (on the same page)... nothing else.. no regard to the failures, wind, etc... purely based on the assumption of landing weight and chosen config...

now you are required to follow the ECAM and QRH procedure in case of any abnormality exactly the way they are displayed...


cheers