Unusual PFD display on a Brand new A 321
 

Hello all,

Last week, I was flying around 31000 feet on a Brand New A321 (MSN 6324) and during the flight the captain noticed that the Green Dot was lower than the VLS. I took a picture and show it to some others captains but all seem confused and do not have an explanation. IF someone have any idea, please share.

We were not in Icing conditions so i doubt it has something to do with the new OEB 45.

http://img11.hostingpics.net/pics/997015PFD.png

Thank you.

@pineteam:
 

Don't see the VLS strip but AFAIK the alpha protect strip is over de green dot and VLS strip,
Do not know the particularities of A320, but if this was A330 I would say something is wrong with one or more AoA vanes.

No Vls strip visible, and the barber higher than green dot? Seems wrong.
Select AIDS on the FMGC, call up alpha code AOA and have a look. Both should read very similar numbers, and in this case around 2.70 degrees.
If not, AOA at fault.

Thanks for the picture - Interesting
Was it a similar display in straight flight ?
Was it a similar display on both PFDs ?
Did you have a look at the ACMS afterwards ?
Did you touch a word about it to maintenance upon arrival ?

It is not necessary to be in icing conditions for the RED OEB (is it 48 for the 320 ?) to be involved. AOA probes can block for various reasons.

This is purely a function of your turn. And just to be clear VLS is not visible in this picture. Same thing happens at all Altitudes, in the A321 you can't hold at green dot most of the time as during the turn green dot gets overtaken by vprot. What you are looking at here is the top of the black and amber bar which is, v prot - the speed at which low speed protections can become active.

Vls is not visible because it is not load factor dependant and Valpha prot and V alpha Max are so they have overtaken Vls.

Also, if you fly at a decent speed then all this messy business is usually hidden off the bottom of the speed tape... 270/M0.72 seems very slow in a 321 at FL310?

I have had a very low speeds computed by the FACs in the past (G-Dot, S, F).
I went on to check the GW computed by the FACs using the Param Alpha Call Up and the weight during approach was below the DOW which was not possible. (13 tons below the actual weight!!)
We went on to fly the approach using selected speed and managed the speed when configured for landing as we knew the speed wouldn't go below the Vapp target computed from the FMS.

On your picture, you can't even see the VLS, you see the V Alpha Prot.

On the return flight everything was fine and it was the very last time i saw this happen.

I think there was some kind of bug because both FAC were computing about the same really low weight.

pineteam, Valmont
I don't see anything wrong with this GD speed, it is 238KTs. At FL of 310 the GW would have been 71 Tons. As I explained in earlier post VLS and GD remain unchanged with increased load factor but Valpha prot and Valpha max increase in a turn since they are load factor dependant, so their overtaking VLS and GD is perfectly normal.

Helo all,

I have a different opinion regardingb the pic.
On the A340 (and could be on new A320) if u change the GW on the Fmgc, this will have impact on Vls and Gd speeds on fmgc and on pfd as well ( but not on alpha speeds).
So, I suspect the pilot has changed fmgc GW.

Thanks

Bank angle ?!?!?
 

Please post a picture in level flight and one more complete picture showing the bank angle during this situation. I think there is a modification for some a320 family a/c showing a alpha prot above VLS.(consult your engineering department).Anyway I think I can have the same result if I manually increase the bank at this altitude. If the situation is not created on purpose (bank angle + spoilers) a check of alpha parameters AOA and aoa3 could clarify if one(or more) AOA probe is blocked or giving erroneous inputs.

Rocket3837 and pilot-737
Why are you after GD speed it is absolutely correct. The issue is not GD but Valpha prot above GD. Which is also normal with increased load factor.
pilot-737 How can there be such modification? Valpha prot and V alpha Max show AoA from ADR 1+2 averaged and converted to speeds. Vls remains constant so can be less than these.

As above, one needs to understand what is a computer calculated speed - and thus susceptible to GIGO - and what is a live sensor derived indication, in turn susceptible to sensor errors.

A combination of AoB, Load Factor (levelling off from descent) will move Alpha Prot quite correctly as anyone who has flown AoA will appreciate...

Hello Vilas,

I'm new on type so I might be confused. But from my little experience and even the captain told me he never saw the Green Dot below Valpha prot. It is usually always above VLS or at high altitude just on top of Valpha prot.



Hello Rocket 3837,

I might be wrong, but in the FCOM (DSC-22-40-30-PFD speed scale Management) it says:
" The FAC controls the speed scale on the PFD:

the FAC computes: VSW,VLS... and the maneuvering speeds: Green Dot Speed, S speed and F speed...."

Even if you insert a wrong GW in the MCDU it will have no effect on the Green dot speed displayed on the PFD.

That's what I undestand.

Sorry I don't have another picture and I did not fly that plane since.

Thank you guys. Merry Christmas to you all! :O

pineteam
This is the case of treating a person for yellow jaundice who just turned out to be a Chinese. As Peter G-W pointed out the speed/Mach for this altitude is rather low. In normal climb or cruise it would be at least .76 which would be closer to 300KTS. The full speed tape runs about 90KTS from top to bottom so this fact is hidden from view. But I gave you the calculations and explanation in the earlier post. Every thing is normal.

Occurred during Direct DOTMI before handover to Chinese airspace? If so I can understand the slow speed ;)

Helo Vilas
I am aware that alpha spds are G loaded and the rest of spds aren't. But looking at the pic, the bank angle is small and doesn't create big G force to the extent of masking the VLS.

On the A340, u can play with GW which will immediately impact yr Vls and Gd on PFD unlike A320s where speeds on Pfd cannot be changed by changing MCDU GW.

So, I will do more reading & investigation on our brand new A320. It might have different logic than old A320s.

On the newer A320's:

ISSUE DESCRIPTION 1
ONE OPERATOR HAS REPORTED THAT:
-FLYING ABOVE FL 350
-THE VLS IS OVERLAPED BY THE ALPHA PROT
SOLUTION
-ABOVE FL 350, SPECIFICATION IS SUCH THAT, VLS COMPUTED VALUE IS SIMILAR TO THE ONE OF ALPHA PROT SPEED.
-AN INCREASE OF THE VLS VALUE OF 2 OR 3 KTS ABOVE FL 350 WAS IMPLEMENTED IN THE FAC STANDARD XXXXX
ISSUE DESCRIPTION 2
In certain conditions (between fl 150 and fl 300) V alpha prot is too high and may exceed green dot speed
SOLUTION
the cause of this phenomenon is a wrong optimization of the speed Calculation law. This misbehavior has been corrected In the fac A321.
Relevant documentation OEB 115/1

(from an old airbus SB) so yes wrong computer coding may give wrong calculations and wrong indications on your pfd ...

Hello C Star,

Thank you for pointing this out! I just found out in a document showing the difference between the brand new A 321 ( MSN 6324) and an slightly older model (MSN 5523)

http://img4.hostingpics.net/pics/261194PFDD.png