A320 /A319 Ref speeds
Thread Starter
Join Date: Feb 2000
Location: with the porangi,s in Pohara
Age: 66
Posts: 983
Likes: 0
Received 0 Likes
on
0 Posts
A320 /A319 Ref speeds
This has been subject to debate on several occassions and I would like to get a definitive answer.
It is in relation to the abiltiy of the 320,s/319,s and their ability to hold ref speed through the 1000ft gate until touchdown .I understand that Vref on the 320 =VLS +5KTS+1/3 of the HW component,whereas the 319 does not use the 5kts....
If this is the case,the speed fluctuations(and i,m talking calm conditions here) in the 319 rarely stabilize at Vref until approx 100 metres....on on several occassions to stay within the "stabilized app" criteria I have had to disconnect the Auto thrust to get the speed to stabilze using manual thrust.
The fluctuations I talk of are around 10-15ts above Vref,out side the app gate criteria.....yet the 320,s will hold and maintain Vref throughout the app.
I have several mates who fly the 318,they say it,s even worse.I have asked company personal,training dept,engineering the same question.....the replys ...it shouldnt happen.....but it does.
Captain j/Old smokey..feel free to explain....PB
It is in relation to the abiltiy of the 320,s/319,s and their ability to hold ref speed through the 1000ft gate until touchdown .I understand that Vref on the 320 =VLS +5KTS+1/3 of the HW component,whereas the 319 does not use the 5kts....
If this is the case,the speed fluctuations(and i,m talking calm conditions here) in the 319 rarely stabilize at Vref until approx 100 metres....on on several occassions to stay within the "stabilized app" criteria I have had to disconnect the Auto thrust to get the speed to stabilze using manual thrust.
The fluctuations I talk of are around 10-15ts above Vref,out side the app gate criteria.....yet the 320,s will hold and maintain Vref throughout the app.
I have several mates who fly the 318,they say it,s even worse.I have asked company personal,training dept,engineering the same question.....the replys ...it shouldnt happen.....but it does.
Captain j/Old smokey..feel free to explain....PB
Thread Starter
Join Date: Feb 2000
Location: with the porangi,s in Pohara
Age: 66
Posts: 983
Likes: 0
Received 0 Likes
on
0 Posts
mate......have done the same thing....also done flaps 3 landings....just to vary the results.....not looking for a fix-it....trying to find out why there is such a difference based on Airbus ,s Philosophy...that if you can fly the 320 ...you can fly the 380.....can of worms here for sure
Thread Starter
Join Date: Feb 2000
Location: with the porangi,s in Pohara
Age: 66
Posts: 983
Likes: 0
Received 0 Likes
on
0 Posts
yeah mate..no worries..congrats!!!!!!!!!...you beauty....because its froggy,it has now become very clear....I thought you said foggy...but froggy is a whole new concept.......my written english is a bad as my spoken
Join Date: Aug 2001
Location: FL250
Posts: 108
Likes: 0
Received 0 Likes
on
0 Posts
In my limited experience , the only time on the 319 that I have experienced the above is when speed brakes have been used on approach and during flap extension.
When this happens , we just go to selected speed for a moment and then back to managed and that seems to do the trick.
When this happens , we just go to selected speed for a moment and then back to managed and that seems to do the trick.
Join Date: Jan 2000
Location: USA
Posts: 167
Likes: 0
Received 0 Likes
on
0 Posts
The 318/319 are much lighter and short coupled compared to the 320; I believe because of that they are much more affected by the air mass and thus the rapid AT movement particularly in gusty winds. Flying a 319 in gusty winds is like trying to control a potato chip...I would think the 318 is worse.
Join Date: Jul 2006
Location: Earth
Age: 61
Posts: 66
Likes: 0
Received 0 Likes
on
0 Posts
Are you modifying your Vapp speed, or leaving it as the computed value?
Are you seeing any of those phenomena related to the landing mass of the aircraft in any way?
All airports, or a specific airport?
What is the average surface tempurature where this occurs?
Which Engines are on your aircraft? IAC or CFM.
And - what may seem like a strange question - what is your typical landing fuel quantity?
Are you seeing any of those phenomena related to the landing mass of the aircraft in any way?
All airports, or a specific airport?
What is the average surface tempurature where this occurs?
Which Engines are on your aircraft? IAC or CFM.
And - what may seem like a strange question - what is your typical landing fuel quantity?
Join Date: Aug 2002
Location: Up north
Posts: 1,657
Likes: 0
Received 0 Likes
on
0 Posts
If you fly managed speed on the 319 Vapp is Vls+5. Personally I tend not to change the Vapp, but rather be fully config and on speed at about 12-1300 feet(CFM)...I find that this usually gives a more stable speed/approach and the AP is then quite able to sort things out on its own...
IF you change Vapp, just remember...for each 5 kts added, increase landing distance by 7%(QRH 4.04)...So, in most cases with the 319 you will have plenty of rwy available...However, one day you will be a bit closer to limits, have a trainer/CAA guy on the jump seat.... "Why the h**l did you not check your landing distance after adding 10 kts to your Vapp??"
/CP
IF you change Vapp, just remember...for each 5 kts added, increase landing distance by 7%(QRH 4.04)...So, in most cases with the 319 you will have plenty of rwy available...However, one day you will be a bit closer to limits, have a trainer/CAA guy on the jump seat.... "Why the h**l did you not check your landing distance after adding 10 kts to your Vapp??"
/CP
Join Date: Jan 2005
Location: north
Posts: 319
Likes: 0
Received 0 Likes
on
0 Posts
Some possible explanations
1. Longer fuselage = more longitudinal stability. Both in yaw and pitch.
2. Longer distance from the stabilizers to wing - more stability. Especially when extending flap
adding alot of pitching moment.
3. The A320 should have a higher Vref than the A319 for the same weight to avoid tailstrike (at least on the 737NG's thats the case). So you will always fly relativly slower with the A319.
Cheers,
M
1. Longer fuselage = more longitudinal stability. Both in yaw and pitch.
2. Longer distance from the stabilizers to wing - more stability. Especially when extending flap
adding alot of pitching moment.
3. The A320 should have a higher Vref than the A319 for the same weight to avoid tailstrike (at least on the 737NG's thats the case). So you will always fly relativly slower with the A319.
Cheers,
M
Join Date: Jun 2000
Location: Paris, France
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
Hello all,
I'm not sure I understood correctly Pakeha Boy's original post. But are you talking about the fact that those airplanes do not maintain the Vapp as it appears on the approach page in the mcdu ?
If yes, it is normal :
The A320 family is the only airplane I know that will have a MOVING speed bug during final approach (in managed speed mode).
That is because it does something that can be quite surprising at first, but makes a whole lotta sense once you've looked into it :
It computes a minimum GROUND Speed during approach with its calculated Vapp and the atc wind you fed him through the mcdu in the approach page. Then during approach, if the actual headwind is stronger (as it often is when above ground) it adds the difference between the planned headwind and the actual headwind to your speed bug, thus maintaining its Minimum Ground Speed.
If actual headwind is lower than what was planned, it sticks to its original computed minimum GS
I hope that wasn't to obscure !
cheers
I'm not sure I understood correctly Pakeha Boy's original post. But are you talking about the fact that those airplanes do not maintain the Vapp as it appears on the approach page in the mcdu ?
If yes, it is normal :
The A320 family is the only airplane I know that will have a MOVING speed bug during final approach (in managed speed mode).
That is because it does something that can be quite surprising at first, but makes a whole lotta sense once you've looked into it :
It computes a minimum GROUND Speed during approach with its calculated Vapp and the atc wind you fed him through the mcdu in the approach page. Then during approach, if the actual headwind is stronger (as it often is when above ground) it adds the difference between the planned headwind and the actual headwind to your speed bug, thus maintaining its Minimum Ground Speed.
If actual headwind is lower than what was planned, it sticks to its original computed minimum GS
I hope that wasn't to obscure !
cheers
Thread Starter
Join Date: Feb 2000
Location: with the porangi,s in Pohara
Age: 66
Posts: 983
Likes: 0
Received 0 Likes
on
0 Posts
crjo....thanks for the interesting reply......can reference,that info for me and post it..ie Airbus Manual, page# and or reference material...PB
Join Date: Feb 2005
Location: Cloud 9
Posts: 69
Likes: 0
Received 0 Likes
on
0 Posts
Well, the magenta bug moves with the ground speed mini function. This means that the autothrust will always have to command the VAPP target and should not be 10/15 knots above it.
I must confess that it happens a lot with our A320's (IAE) where the speed is between 5 to 10 knots above the VAPP target.
FCOM Volume 3, chapter 4, section 10:
VREF : Reference speed used for normal final approach.
Equal to 1.23 × VS of configuration FULL.
Displayed on the MCDU APPR page if landing is planned in CONF FULL (VLS CONF FULL)
VAPP : Final approach speed.
Displayed on MCDU APPR page.
Calculated by the FMGCs.
Represents : VAPP = VLS + wind correction + 5 knots.
The flight crew may modify VAPP through the MCDU. During autoland or when A/THR is on or in case of ice accretion or gusty crosswing greater than 20 knots, VAPP must not be lower than VLS + 5 knots.
VAPP TARGET : Represented by a magenta triangle.
Calculated by the FMGCs
Gives efficient speed guidance in approach during various windy conditions.
Represents :
VAPP TARGET = GS mini + actual headwind (measured by ADIRS)
GS mini = VAPP - TOWER WIND (headwind component along runway axis calculated by FMGC from tower wind entered on MCDU).
FCOM Volume 1, chapter 22, section 30 :
SPEED MODE IN APPROACH PHASE
When the aircraft flies an approach in managed speed, the speed target displayed on the PFD in magenta, is variable during the approach.
This managed speed target, is computed in the FMGS using the "ground speed mini function".
GROUND SPEED MINI FUNCTION PRINCIPLE
The purpose of the ground speed mini function is to take advantage of the aircraft inertia, when the wind conditions vary during the approach. It does so by providing the crew with an adequate indicated speed target. When the aircraft flies this indicated speed target, the energy of the aircraft is maintained above a minimum level ensuring standard aerodynamic margins versus stall.
If the A/THR is active in SPEED mode, it will automatically follow the IAS target, ensuring an efficient thrust management during the approach.
The minimum energy level is the energy level the aircraft will have at touch down if it lands at VAPP speed with the tower reported wind as inserted in the PERF APPR page.
The minimum energy level is represented by the Ground Speed the aircraft will have at touchdown. This Ground Speed is called "GROUND SPD MINI".
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".
The lowest speed target is limited to VAPP.
The speed target is displayed on the PFD speed scale in magenta, when approach phase and managed speed are active. It is independent of the AP/FD and/or ATHR engagements.
Wind is a key factor in the ground speed mini function.
TWR WIND
It is the MAG WIND entered in the PERF approach page. It is the average wind as provided by the ATIS or the tower. Gusts must not be inserted, they are included in the ground speed mini computation.
TWR HEADWIND COMPONENT
The TWR HEADWIND COMPONENT is the component of the MAG WIND projected on the runway axis (landing runway entered in the flight plan). It is used to compute VAPP and GS mini.
CURRENT HEADWIND COMPONENT
The actual wind measured by ADIRS is projected
on the aircraft axis
to define the CURRENT HEADWIND COMPONENT (instantaneous headwind).
The CURRENT HEADWIND COMPONENT is used to compute the variable speed target during final (IAS target).
VAPP COMPUTATION
VAPP, automatically displayed on the MCDU PERF APPR page, is computed as follows :
VAPP = VLS + 5 + 1/3 of the TWR HEADWIND COMPONENT
"1/3 of the TWR HEADWIND COMPONENT" has 2 limits :
0 knots as the minimum value (no wind or tailwind)
+ 15 knots as the maximum value.
The crew can manually modify the VAPP and TWR wind values on the PERF APPR page.
SPEED TARGET COMPUTATION
The FMGS continuously computes a speed target (IAS target) that is the MCDU VAPP value plus an additional variable gust.
The gust is the instantaneous difference between the CURRENT HEADWIND COMPONENT and the TWR HEADWIND COMPONENT. It is always positive (or equal to zero for no wind or tailwind).
The IAS target is displayed on the PFD as a magenta triangle moving with the gust variation. VAPP is the IAS target minimum value.
GROUND SPEED MINI (GS mini) COMPUTATION
Ground speed mini concept has been defined to prevent the aircraft energy from dropping below a minimum level during final approach. The GS mini value it is not displayed to the crew.
I must confess that it happens a lot with our A320's (IAE) where the speed is between 5 to 10 knots above the VAPP target.
FCOM Volume 3, chapter 4, section 10:
VREF : Reference speed used for normal final approach.
Equal to 1.23 × VS of configuration FULL.
Displayed on the MCDU APPR page if landing is planned in CONF FULL (VLS CONF FULL)
VAPP : Final approach speed.
Displayed on MCDU APPR page.
Calculated by the FMGCs.
Represents : VAPP = VLS + wind correction + 5 knots.
The flight crew may modify VAPP through the MCDU. During autoland or when A/THR is on or in case of ice accretion or gusty crosswing greater than 20 knots, VAPP must not be lower than VLS + 5 knots.
VAPP TARGET : Represented by a magenta triangle.
Calculated by the FMGCs
Gives efficient speed guidance in approach during various windy conditions.
Represents :
VAPP TARGET = GS mini + actual headwind (measured by ADIRS)
GS mini = VAPP - TOWER WIND (headwind component along runway axis calculated by FMGC from tower wind entered on MCDU).
FCOM Volume 1, chapter 22, section 30 :
SPEED MODE IN APPROACH PHASE
When the aircraft flies an approach in managed speed, the speed target displayed on the PFD in magenta, is variable during the approach.
This managed speed target, is computed in the FMGS using the "ground speed mini function".
GROUND SPEED MINI FUNCTION PRINCIPLE
The purpose of the ground speed mini function is to take advantage of the aircraft inertia, when the wind conditions vary during the approach. It does so by providing the crew with an adequate indicated speed target. When the aircraft flies this indicated speed target, the energy of the aircraft is maintained above a minimum level ensuring standard aerodynamic margins versus stall.
If the A/THR is active in SPEED mode, it will automatically follow the IAS target, ensuring an efficient thrust management during the approach.
The minimum energy level is the energy level the aircraft will have at touch down if it lands at VAPP speed with the tower reported wind as inserted in the PERF APPR page.
The minimum energy level is represented by the Ground Speed the aircraft will have at touchdown. This Ground Speed is called "GROUND SPD MINI".
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".
The lowest speed target is limited to VAPP.
The speed target is displayed on the PFD speed scale in magenta, when approach phase and managed speed are active. It is independent of the AP/FD and/or ATHR engagements.
Wind is a key factor in the ground speed mini function.
TWR WIND
It is the MAG WIND entered in the PERF approach page. It is the average wind as provided by the ATIS or the tower. Gusts must not be inserted, they are included in the ground speed mini computation.
TWR HEADWIND COMPONENT
The TWR HEADWIND COMPONENT is the component of the MAG WIND projected on the runway axis (landing runway entered in the flight plan). It is used to compute VAPP and GS mini.
CURRENT HEADWIND COMPONENT
The actual wind measured by ADIRS is projected
on the aircraft axis
to define the CURRENT HEADWIND COMPONENT (instantaneous headwind).
The CURRENT HEADWIND COMPONENT is used to compute the variable speed target during final (IAS target).
VAPP COMPUTATION
VAPP, automatically displayed on the MCDU PERF APPR page, is computed as follows :
VAPP = VLS + 5 + 1/3 of the TWR HEADWIND COMPONENT
"1/3 of the TWR HEADWIND COMPONENT" has 2 limits :
0 knots as the minimum value (no wind or tailwind)
+ 15 knots as the maximum value.
The crew can manually modify the VAPP and TWR wind values on the PERF APPR page.
SPEED TARGET COMPUTATION
The FMGS continuously computes a speed target (IAS target) that is the MCDU VAPP value plus an additional variable gust.
The gust is the instantaneous difference between the CURRENT HEADWIND COMPONENT and the TWR HEADWIND COMPONENT. It is always positive (or equal to zero for no wind or tailwind).
The IAS target is displayed on the PFD as a magenta triangle moving with the gust variation. VAPP is the IAS target minimum value.
GROUND SPEED MINI (GS mini) COMPUTATION
Ground speed mini concept has been defined to prevent the aircraft energy from dropping below a minimum level during final approach. The GS mini value it is not displayed to the crew.
Last edited by Pander216; 10th Aug 2006 at 22:34.
Thread Starter
Join Date: Feb 2000
Location: with the porangi,s in Pohara
Age: 66
Posts: 983
Likes: 0
Received 0 Likes
on
0 Posts
Pander mate,.thanks for the reference and have read this info .....your ref for the 320 (Vapp) is not the same computed for the 319 and this is where the disparity occurs.
I let the posts go for several days as I was scheduled on a 4 day trip and decided to take some of the input given by other posters...Capt Jeeves,noting your questions......I made several apps,all early morning,all calm conditons,15-20kmn finals as to stabilize all apps.......Vapp on all were within acceptable profile limits.
The problem occurs(this will sound obvious) in afternoon arrivals where,as previoulsy mentioned,wind velocities at differing altitudes change,but there is a marked change,but it seems the 319,s reaction to these wind changes is an "overput" of power to maintain Vapp(in the managed mode,AP/ATHR),thus giving larger speed variations.
The 319 does seem to be able to handle the inputs as well as the 320
I let the posts go for several days as I was scheduled on a 4 day trip and decided to take some of the input given by other posters...Capt Jeeves,noting your questions......I made several apps,all early morning,all calm conditons,15-20kmn finals as to stabilize all apps.......Vapp on all were within acceptable profile limits.
The problem occurs(this will sound obvious) in afternoon arrivals where,as previoulsy mentioned,wind velocities at differing altitudes change,but there is a marked change,but it seems the 319,s reaction to these wind changes is an "overput" of power to maintain Vapp(in the managed mode,AP/ATHR),thus giving larger speed variations.
The 319 does seem to be able to handle the inputs as well as the 320
