A320 QNH Correction to V2

[Haroon]

https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/1382x691/perf_quest_0b59a7eec41d7a1c05e23b1c87725bbc5ef808fa.png
Can someone please throw some light on this, thanks.

[Goldenrivett]

It must be a printing error - you can't have V2 below VR.
If you look at the corrections published for -10 Kts and +10 Kts, they show only -1 Kt correction which makes the results sensible.

[gearlever]

Maybe for flat earth only:rolleyes:

[joe falchetto 64]

https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/1382x691/perf_quest_0b59a7eec41d7a1c05e23b1c87725bbc5ef808fa.png
Can someone please throw some light on this, thanks.

To have the proper answer you must check the Maximum Permissible Take Off Weight for the airport and runway in use. After that compare the speeds . Remember that no correction on speeds is required if applying bleed and qnh correction to flex take off. Refers to PER-TOF-TOC-20–10 P 5/14 “Correction produced on the RTOW chart” para 2 last sentence.

[Haroon]

It must be a printing error - you can't have V2 below VR.
If you look at the corrections published for -10 Kts and +10 Kts, they show only -1 Kt correction which makes the results sensible.
I have seen it on some other charts too and not only on this one.
https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/1202x621/perf_quest2_6cb8712b021cf52bad5753d566aba04845b6cadc.png
https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/1206x701/perf_quest3_d19f706bab11a3770154eeb7c10092627d1bc59e.png

[Haroon]

To have the proper answer you must check the Maximum Permissible Take Off Weight for the airport and runway in use. After that compare the speeds . Remember that no correction on speeds is required if applying bleed and qnh correction to flex take off. Refers to PER-TOF-TOC-20–10 P 5/14 “Correction produced on the RTOW chart” para 2 last sentence.

Correct! But lets assume its not a flex case e.g. OAT is 44, QNH is 1003 and actual TOW is 70.5 tons. The speed correction will be applicable in this case right?

[sonicbum]

Hi,

the reference is in PER-TOF-TOC-12-10 P 5/14 (TEMPERATURE ENTRY).

(...)Check that the resulting speeds are higher than the minimum speeds displayed on the RTOW
chart and that V2 is higher than the VMU limited speed (Refer to PER-TOF-TOD-25-20 MINIMUM
V2 LIMITED BY VMU/VMCA (KT IAS)).

(...)If OAT is higher than TVMC (line 3) or if the above speed check is not fulfilled, apply ΔW correction
from line 3 and ΔV1/ΔVR/ΔV2 corrections from line 4. No speed check is required.

Your speed are 149/150/151.

[Haroon]

Hi
Hi,

the reference is in PER-TOF-TOC-12-10 P 5/14 (TEMPERATURE ENTRY).

(...)Check that the resulting speeds are higher than the minimum speeds displayed on the RTOW
chart and that V2 is higher than the VMU limited speed (Refer to PER-TOF-TOD-25-20 MINIMUM
V2 LIMITED BY VMU/VMCA (KT IAS)).
(...)If OAT is higher than TVMC (line 3) or if the above speed check is not fulfilled, apply ΔW correction
from line 3 and ΔV1/ΔVR/ΔV2 corrections from line 4. No speed check is required.


The Note on the same page say: "No speed check is required for the first correction".

In any case the min V speeds on that chart are:
https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/438x100/min_speedspng_08b3326973962b9f7c396e32b015aa9c5cbd81dc.png
which are way below.

Your speed are 149/150/151.
How did you determine that? You've only reduced V1 whereas the correction applies to all.

[FlightDetent]

Haroon, you need to check with your Flight Operations Engineering department, and they probably with Airbus.

It makes no sense, and I think the explanations provided so far are valid for something else than you asked about.

To reiterate my understanding of your original question:
In case you needed to apply the speed corrections for low QNH, the resulting V2 is invalid. How come?
​

​​​​​

[Haroon]

Harpoon, you need to check with your Flight Operations Engineering department, and they probably with Airbus.​​​​​

Thanks, I guess so.

In case you needed to apply the speed corrections for low QNH, the resulting V2 is invalid. How come?

That's correct.

I would be grateful if some A320 pilots could have a quick glance in their books to see if they could find similar sort of stuff. Thanks.
​

[sonicbum]

Thanks, I guess so.



That's correct.

I would be grateful if some A320 pilots could have a quick glance in their books to see if they could find similar sort of stuff. Thanks.
​

Haroon, I haven't seen initially the minimum speed You have published, hence my answer does not apply to Your question. Best thing as suggested is to mail Your perf dept. and check with them.

[Haroon]

Thank you. Query already sent, lets see what do they have to say.

[sonicbum]

Thank you. Query already sent, lets see what do they have to say.

Cheers. Let us know the answer. For some reasons (not sure which:)) I believe it will end up by applying the corrections from line 3 and 4 so that V2 is not lower than Vr.

[FlightDetent]

Cheers. Let us know the answer. I am quite curious too.

[Haroon]

Will share with all :)

[Haroon]

The reply was:
"Software is designed to calculate Charts including speeds and corrections separately. After applying corrections if V2 decreases from VR then apply the basic performance rules and take V2 equal to VR."