How does the PFD show (calculate) wind velocity during the takeoff roll ?
 

I understand that velocity triangle can calculate wind velocity, but during the ground roll on takeoff how will this be done? Appreciate answers.

It can't.

In order to calculate the wind it needs to know the ground speed vector, aircraft heading and TAS.

During take off, the difference between ground speed and TAS is displayed as a head wind all of which appears to be on the nose. Once airborne and the aircraft senses the drift then the wind speed vector will be more truthful.

Rubbish. (ten characters added).

Not being an Airbus guru, I'd have to ask which models are equipped with a side-slip vane? I know I've seen them on at least some models.

If so equipped wouldn't it be possible that measured side-slip angle could be incorporated into the wind triangle calculation?

Takeoff run:
ADC calculated TAS = 100 kts
GPS calculated GS = 80 kts
Weight on wheels = TRUE
Wheel speed sensors = 80 kts
Rwy HDG = 090 deg.
GPS calculated track = 090 deg. (drift angle = 0 deg.)
Side-slip sensor angle = 5 deg.

From the above provided data, can the direction and velocity of the wind be determined?

Of course it can.

Knowing the side-slip angle can also be used to apply pitot/static pressure corrections based on tables derived from flight test data.

So does Airbus incorporate this calculation capability to display actual wind direction and velocity on the PFD during takeoff? It doesn't seem all that daunting a task given the availability of sufficient data processing capability.

I'd like to see what an avionics tech familiar with these systems has to share regarding this capability.

Previous thread:

http://www.pprune.org/tech-log/27329...eoff-roll.html

As an aside it might be worth noting that certainly on at least one Boeing the use of the "wing down" (side slip) technique for final approach /landing stuffs up the wind vector calculations....

It is merely a theoretical question. The very fact wind is displayed on ND and not on PFD means on take off wind display has no meaning. At take off surface wind given by the tower is enough to start with and any change PF will notice by changing rudder requirement. Pilots monitor speed trend arrow which shows the acceleration. Normally the arrow head disappears on top. If it reappears and shortens or fluctuates it is a sign of wind shear and abort should be considered.

@peekay4. Nice thread, but still doesn't answer.
Guess must be the different static pressures during roll as there are no sides lip vanes on A320.

Why would airbus use anything complicated to calculate drift etc. when the use of wind display is not meant for the take off run? I don't know how many pilots look at ND during take off run. It is straight calculation airspeed-GS and once airborne it works by including HDG/TRK difference.

It's not about why it's done, required or not, should look at it or not BUT HOW DOES IT DO SO.

Exactly Vilas. But I used to (retired now) have a quick glance at the ND wind at 100kts just to make sure the indicated component was what I was expecting.

This question is further confused by some sims incorrectly indicating the IOS w/v at 100kts rather than the component.
It does look rather odd though if taking off with 30kts across that the 100kt ND w/v reads 000/00

Cheers all
mcdhu

What did you do in cases when it wasn't?

I don't have any idea. But I thought the original question was interesting from a technical point of view. If it could be done, then how?

For what purpose the information may be useful (if displayed) is another discussion. What useful purpose does allot of the available information serve? How long is a string?

As for myself, if I'm PF I'm almost exclusively eyes outside once the thrust is set. As PM I scan several things.

aquarium1 asked the question and goldenrivet answered. Rest is trying to find the provebial black cat in dark room which is not there. Usefulness of wind vector on takeoff run, has any SOP ever asked you to use it on the run? No.

aquarium1
. To start with is it too much to expect that you should know PFD is not the place to look for wind velocity? It's effects on airspeed is a different matter. To the second question, since it doesn't do it any differently on ground than in the air has errors of that constraint.

Any pilot thinking of performing a high energy take off abort because of an unreliable calculated wind vector, produced on the ground on the ND should probably buy a six pack, grab a chair, sit in the back yard and rethink his or her whole abort criteria over again.

How many passengers have we, collectively as an industry, killed because of unrequired high speed aborts?

Below 100 knots "Stop, Stop, Stop."

Above 100 knots "Go, Go, Go." (EXCEPT under the conditions your operator specifies, and I have yet to learn of one which references ND wind speed component)

a_pilot
Sure! Trend arrow is a very good indication of wind shear and aircraft acceleration but not the wind on ND. Monitoring of ND wind component is not mentioned in any airbus document nor is it required because there is no way it can calculate the vector correctly on ground. No action is recommended in any document on the basis of ND wind on take off. Normally Trend vector disappears on top but if it reappears, fluctuates or shortens TOGA is an option if stopping in remaining runway is doubtful. But ND wind plays no part in that decision. FCOM below:
The takeoff should be rejected only if significant airspeed variations occur below indicated V1 and the pilot decides that there is sufficient runway remaining to stop the airplane.

If Airbus had wanted you to montitor it, it would be on the PFD nice and big. Like a trend vector.

On takeoff roll (which as you are aware is the subject of discussion) I don't:
- monitor the E/WD and SD
- monitor navigation/weather returns at all on the ND
- regularly monitor aircraft systems in the SD
- monitor the TAT and SAT and just guess the temperature somehow
- monitor gross weight.

Do you?

The only clarification to the above is that the PM does monitor the E/WD during takeoff. And I'll glance at it at times if I'm PF.

'a pilot', re #19, it's the piloting skill which enables him/her to understand the quality of information and the circumstances (need) for use; not the perceived ability to use all available information.
Skill involves knowledge, such as how the wind speed display is calculated, it's accuracy, update rate, and relevance for flight condition.

Wind-shear during take off is best avoided with preflight assessment and planning; if a warning is encountered during takeoff then stick with the procedures - 'If ... Then', don't invent your own qualifiers, '... Except', (what is the action with a WS warning but no change in wind speed indication).
For every 'good idea' (opinion) the greater the opportunity for ill-considered 'bad' outcomes. Where is the line between stop and go for a 'slight wind change', is it chosen for each takeoff, what is it based on, what speed, ... each additional variable adds to the complexity of operation and the likelihood of misjudgement