A321 - Vapp in PFD different from MCDU
Thread Starter
Join Date: Oct 2010
Location: Lisbon
Posts: 15
Likes: 0
Received 0 Likes
on
0 Posts
A321 - Vapp in PFD different from MCDU
Hello all,
Today we're approaching and the Vapp calculated in the MCDU was 141 kts but the magenta triangle in the PFD was at 160 kts.
We had managed speed and the wind was 240/15kts no gust reported for rwy 23.
Is it possible to have such indication with constant wind?
We landed a litle bit faster than normal but safe. I was reading the FCOM former 1.22.30 p68 and it makes sense that our IAS moves when we have current wind different from the wind reported (GS mini) but this was not the case of today.
can anyone please explain why such difference?
Thanks to all
Today we're approaching and the Vapp calculated in the MCDU was 141 kts but the magenta triangle in the PFD was at 160 kts.
We had managed speed and the wind was 240/15kts no gust reported for rwy 23.
Is it possible to have such indication with constant wind?
We landed a litle bit faster than normal but safe. I was reading the FCOM former 1.22.30 p68 and it makes sense that our IAS moves when we have current wind different from the wind reported (GS mini) but this was not the case of today.
can anyone please explain why such difference?
Thanks to all
Join Date: Oct 2009
Location: UK
Posts: 1,270
Likes: 0
Received 0 Likes
on
0 Posts
Hi dovish,
TTex600 is correct. You probably had a head wind component during the approach which was about 20kts greater than the surface wind value you'd entered in the FMGC.
FCOM 1.22.30 Autothrust
"During the approach, the FMGS continuously computes the speed target, using the wind experienced by the aircraft, in order to keep the ground speed at or above the "Ground Speed Mini"."
We used to do the same maths on 707s using INS "WIND HOLD" for the instantaneous wind component on the approach, and adjusted our approach speed depending on the reported tower wind (exactly as ground speed mini does now). The power only changed to suit the ROD, and not to chase the temporary gusts or wind shear.
It's so much simpler now.
TTex600 is correct. You probably had a head wind component during the approach which was about 20kts greater than the surface wind value you'd entered in the FMGC.
FCOM 1.22.30 Autothrust
"During the approach, the FMGS continuously computes the speed target, using the wind experienced by the aircraft, in order to keep the ground speed at or above the "Ground Speed Mini"."
We used to do the same maths on 707s using INS "WIND HOLD" for the instantaneous wind component on the approach, and adjusted our approach speed depending on the reported tower wind (exactly as ground speed mini does now). The power only changed to suit the ROD, and not to chase the temporary gusts or wind shear.
It's so much simpler now.
Thread Starter
Join Date: Oct 2010
Location: Lisbon
Posts: 15
Likes: 0
Received 0 Likes
on
0 Posts
I noticed it close to threshold and it remained like that until touchdown.
Probably one will say that we had wind more than reported from tower and it was just the GSmini in action that added around 20 kts more but I can say that the wind we were experience was not like that.
I just hope to fly the same aircraft again and I will pay more attention to it.
Thanks a lot for the feedback.
Probably one will say that we had wind more than reported from tower and it was just the GSmini in action that added around 20 kts more but I can say that the wind we were experience was not like that.
I just hope to fly the same aircraft again and I will pay more attention to it.
Thanks a lot for the feedback.
Join Date: Jun 2002
Location: Vega Constellation
Posts: 286
Likes: 0
Received 0 Likes
on
0 Posts
It could also be that the MCDU entered weight differed a lot from the actual weight calculated by the FAC during climb.
You will get an error message "CHECK GW" on the MCDU only if the MCDU and FAC values differ by more than 7 (seven) tons. That could make for a lot of speed! A finger trouble or a W&B miscalc could easily make up for that. If the weight is/was verified to be absolutely correct (is it a word in aviation?..) then the AOA probes may need a check up.
Just a guess.
Flex
You will get an error message "CHECK GW" on the MCDU only if the MCDU and FAC values differ by more than 7 (seven) tons. That could make for a lot of speed! A finger trouble or a W&B miscalc could easily make up for that. If the weight is/was verified to be absolutely correct (is it a word in aviation?..) then the AOA probes may need a check up.
Just a guess.
Flex
Last edited by FLEXPWR; 6th Jan 2012 at 23:48. Reason: typo
