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Flying below VAPP - What to do ?

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Flying below VAPP - What to do ?

Old 8th Aug 2015, 08:48
  #21 (permalink)  
 
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Originally Posted by Zenj View Post
on approach with auto thrust on , you find speed going below VAPP or even getting to VLS , what do you do to recover back to your VAPP ?

Thanks
Wait... what's the problem with the speed going to Vls ? Give it a second or two and you will be back to Vapp.
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Old 8th Aug 2015, 09:03
  #22 (permalink)  
 
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"on approach with auto thrust on , you find speed going below VAPP or even getting to VLS , what do you do to recover back to your VAPP"
There can be two situations causing this to happen. One is ATHR unable to respond to rapidly changing situation. In that case manual thrust is an option. The second is if the down drafts are beyond the capability of CLB thrust value itself, in that case the thrust will be already at CLB and flying in manual thrust or select speed is not going to help and you cannot increase thrust without going past CLB gate which is not recommended anymore. If you are on GS you may push the nose down to go down to permitted deviation value to see if the conditions improve but if already low and slow pushing nose down is not an option. If you are nearing 1000ft. AGL only option is to GA and attempt another landing in lesser configuration like Flap3.
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Old 8th Aug 2015, 09:51
  #23 (permalink)  
 
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I used to like the nudging the TL's out of CL to cure the problem, but banned in our outfit now.
Always check that you have a good 5kt between VLs and the bugged Vapp after landing flap selected. Adjust Vapp in the MCDU if not. Even 2kts makes a significant difference to the lazy Airbus ATHR.
If it really gets out of hand take the automatics out.
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Old 8th Aug 2015, 13:53
  #24 (permalink)  
 
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I much prefer the Boeing A/T setup over the Bus any day of the week.....

Having said that the Bus system works ok, takes a little getting used to after the simple Boeing but it works ok.

The thrust bump technique is indeed still in the latest updated A330 FCTM we have and it's approved by Airbus.....( as I posted way back )
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Old 8th Aug 2015, 16:51
  #25 (permalink)  
 
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Originally Posted by john_smith View Post
We have this SOP in our outfit too. It's not an Airbus technique. According to Airbus, the VLs computed by the FMGC and displayed on the PERF page is more accurate than the VLs displayed on the PFD computed by the FAC. The FMGC computes Vapp as VLs+5kts so Airbus philosophy is to leave it alone under normal conditions (not gusty crosswind etc.). I think this five knot gap thing is an airline response to perceived tail strike risk.
On latest MSNs you have consistent informations between the PFD and MCDU as the FAC computes operating speeds based on the FMS gross weight.
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Old 10th Aug 2015, 11:23
  #26 (permalink)  
 
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Lots of Top Gun pilots here!

But it is a good question, because there is more to it than it meets the eye.

First, you can make hundreds of landings and the sluggish A-330 A/THR will lag many times, without going below VLS, but well below VAPP. Below VLS is indeed a rare event (seen it twice in 4 years)

Second: GS MINI is fantastic, except if you are in the A-330 with its sluggish A/THR. When you see you are 6 kt below VAPP and increasing and thrust doesn't move a freaking decimal of N1% even after several seconds, you have at least the right to name it sluggish.

Third: If you are flying the A-330 on behalf of an airline full of OM stabilized approach restrictions and FOQA, this scenario is way different than if you are in a more relaxed, pilot friendly or pirate airline. In the former, you can be sacked or demoted for an unstable approach, so if you have this situation at 500 or below, you should go around. Or shouldn't you? How many knots below VLS should trigger the go around decision? Depending on the trend? What is my ops department opinion regarding that matter?

There are deviation call outs. The question is What do you do when the PM says "speed" and A/THR is engaged?

a) disconnect the A/THR and carry on manually
b) do the thrust levers momentarily above CLB detent technique
c) say "correcting" and hope that the A/THR decides to correct and start increasing N1, at least enough for the trend to be on the recovery side, we will be good soon before flare, lets see...
d) go around because you are not stabilized anymore.

You might very well decide a), b) or c) and then be sacked. Even Maverick could be sacked for that (and Gus sent to CRM rehab. "I got your tail, man").
You might choose d) and then be questioned about an unnecessary go around "come on, man, it was 2 knots and already with positive trend, be a man". Some good airlines will not question a go around, but others will.

So the question that the original poster made is a very good one, indeed.
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Old 10th Aug 2015, 11:32
  #27 (permalink)  
 
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My previous fleet manager told me that Airbus A/THR maintains bug plus or minus 5kts, whereas we pilots prefer to see a range of bug to bug +10kts. In other words, we are uncomfortable seeing speed less than bug, but the aircraft design has taken this into account and it is OK.

In addition, on approach the Airbus minimum groundspeed system keeps the groundspeed constant - which is more relevant for landing - rather than the airspeed, and although mini G/S is very good and safe system, its variations are perhaps not totally intuitive to pilots who are programmed to keep airspeed controlled.

Having said that, the 330 did sometimes give me cause for concern, and I really liked the "phase advance" technique of pushing the thrust levers forward of the CLB detent and back to "wake up" the A/THR.

Problem with that was, some pilots would push the levers forwards and leave them there for several seconds, by which time the engines would be producing far too much power and destablise the ship. All that was required in phase advance was click out click back, in the same time it takes to say that out loud. But as usual it was never explained properly and some folk got it wrong, so they banned the whole thing. Shame.

Last edited by Uplinker; 11th Aug 2015 at 10:32.
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Old 10th Aug 2015, 11:41
  #28 (permalink)  
 
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Airbus minimum groundspeed system keeps the groundspeed constant - which is more relevant for landing - rather than the airspeed
I disagree. Airspeed is always relevant and primary. GS mini just adapts the speed target to maintain that computed minimum GS that will protect you from a possible gust. So when the gust hits you, the extra knots given to your target speed by GS MINI to the are 'spent', their role has been fulfilled and the target decreases to the new value after the gust. Nice!

However it will not suffice if the gust is worse than anticipated (some think that GS MINI will protect you from any gust no matter the intensity) specially if the A/THR is sluggish.
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Old 10th Aug 2015, 12:49
  #29 (permalink)  
 
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UPLINKER:----ok I'll challenge you statement that it was banned, by who? Certainly not Airbus.

This is the latest A330 FCTM that our company must get approved by Airbus............

It CLEARLY advocates the use of this technique.

In gusty wind conditions, the A/THR response time may be insufficient to cope with an instantaneous loss of airspeed. A more rapid thrust response can be achieved by moving the thrust levers above the CL detent (but below MCT). The thrust will quickly increase towards the corresponding TLA. The A/THR remains armed and becomes active immediately the thrust levers are returned to the CL detent. Therefore, the thrust levers should be returned to CL detent as soon as there is a positive speed trend. However, there are two important points to note:

‐ Selecting the thrust levers to the TOGA detent, even momentarily, will engage the Go-Around mode,


and. ‐ In some aircraft selecting the thrust levers above the CL detent below 100 ft RA will disconnect the A/THR. In this case, returning the thrust levers to the CL detent will set climb thrust. Refer to FCOM DSC-22_30-90.
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Old 10th Aug 2015, 18:28
  #30 (permalink)  
 
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Originally Posted by Microburst2002 View Post

Third: If you are flying the A-330 on behalf of an airline full of OM stabilized approach restrictions and FOQA, this scenario is way different than if you are in a more relaxed, pilot friendly or pirate airline. In the former, you can be sacked or demoted for an unstable approach, so if you have this situation at 500 or below, you should go around. Or shouldn't you? How many knots below VLS should trigger the go around decision? Depending on the trend? What is my ops department opinion regarding that matter?

There are deviation call outs. The question is What do you do when the PM says "speed" and A/THR is engaged?

a) disconnect the A/THR and carry on manually
b) do the thrust levers momentarily above CLB detent technique
c) say "correcting" and hope that the A/THR decides to correct and start increasing N1, at least enough for the trend to be on the recovery side, we will be good soon before flare, lets see...
d) go around because you are not stabilized anymore.

You might very well decide a), b) or c) and then be sacked. Even Maverick could be sacked for that (and Gus sent to CRM rehab. "I got your tail, man").
You might choose d) and then be questioned about an unnecessary go around "come on, man, it was 2 knots and already with positive trend, be a man". Some good airlines will not question a go around, but others will.

So the question that the original poster made is a very good one, indeed.
Hi MB,

I believe that even in your airline if stabilized criteria are met during the approach and subsequently there are minor deviations due to environmental conditions then it is accepted. If you believe, according to your airmanship, that it is not "minor" anymore, than go around. You can be questioned for a go around for sure, but not more than questioned unless something happens during the go around of course.
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Old 10th Aug 2015, 20:44
  #31 (permalink)  
 
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That is what I don't like. I don't want to have to decide how long is too long, and how many knots are too many, or how much is "minor".

It remains a mystery why the A/THR is so bad in approach in the A-330. It is very frustrating when it freezes no matter what.
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Old 11th Aug 2015, 11:20
  #32 (permalink)  
 
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Hi ACMS, I meant that my company banned the procedure, but the impression I got was that it came from Airbus. I am delighted that it is not banned by Airbus (with caveats), and will therefore keep it in my back pocket for those hot, thermally approaches which sometimes confuse the A330.
Cheers !

Hi Micro, yes, perhaps my meaning was not very clear. GS mini is an airspeed target which is computed according to the tower wind and any detected wind changes on approach, and is followed by the A/THR to keep the groundspeed above a certain minimum, based on the groundspeed required at touchdown. When the headwind increases above the tower headwind the GS mini increases its target, increasing indicated airspeed to maintain the groundspeed.

In my experience it does a very good job but obviously, really big gusts can upset this, as they can upset anything.

I wonder if Airbus forgot to program the "Approach autothrust" mode into the A330? (This mode makes the autothrust more responsive to speed variation below 3200' rad alt.)
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Old 11th Aug 2015, 14:57
  #33 (permalink)  
 
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MB if you fly an approach in gusty wind conditions speed excursions are just going to happen, there is nothing you can do about it, regardless of the A/THR being ON or OFF.
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Old 11th Aug 2015, 14:59
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I know what GS mini is and how it works. The problem here is that the A/THR fails to keep the speed target, for no known reason (N1 steady, no reaction).
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Old 11th Aug 2015, 15:01
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sonic

In some cases the gusts are slow and there is plenty of time to counter them, only the A/THR is just frozen. In manual thrust it would be easy. I wonder what is the reason.
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Old 11th Aug 2015, 15:19
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As it appears, in the A-330 IAS TARGET computation differs when below 400 AGL.
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Old 11th Aug 2015, 22:30
  #37 (permalink)  
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I'm very much disappointed by post from John_Smith !

He calls me someone not a pilot and doing things in the MSFS , well just for your information I have been flying for 30 years and mainly on the Boeing and its just these last 2 years that I have gone to the Airbus and just ask anyone flying the Boeing, A/T is not an issue as long as you can follow it with other parameters and almost all Boeing pilots are good at flying manually with A/T Disconnected.

Have you read the recently released AAIB report of the British Airways A319 that lost cowlings in the air and eventually leading to engine fire ?

The commander had not flown with manual thrust for the past 7 years before accident and F/O had never flown completely in the aircraft.

FYI i have the knowledge mentioned but I have seen speeds going below VAPP and close to VLS on one of the aircrafts and this is the reason I asked because I'm told Airbus did have a procedure before but now it has been removed on A320's.

The bottomline is , we are here in this particular forum to learn and there is no pilot who is perfect , we have seen the best pilots doing the most silly things that turned into disasters.

So Mr. John Smith, please do not accuse or tarnish people here by just asking questions , if you find them silly please just hit the back button and do something else, the 3,098 views and almost 40 posts were not useless people but these are pilots trying to support and some trying to learn !

Thanks always for those who take their time to explain things !
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Old 11th Aug 2015, 22:53
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I do not know about other FBW a/c, including military. Are AB the only manufacturer who has designed static thrust levers? If so, they have also designed these, what seem to be, confusing 'gates' of thrust. Why try to reinvent the wheel? Forward = more umph and backward = less. The pilots decides. If he wants G/A he activates a G/A button and shoves the levers away from him. If he wants to land and slow down he pulls them towards him.
I'm an old soul and it all sounds so simple. All these thrust gates, and activating G/A mode by surprise and landing mode by surprise seems too much of a surprise for me. I think flying should be intuitive. This seems complicated. There will be those who say; "ah, but when you get used to it it is OK". Now we all know some are sharper than others. Some may never get used to it. They've been told to let George do his thing and you'll be alright. It can't fail. Well we've all seen were that has led to. I'm trying to fathom the benefit of having static thrust levers in A/T mode and all these various automatic mode activated gates. If ever there was a cause for "what the [email protected]Łk is it doing now?" then surely this is it.
I stand to be corrected and learn from my peers. I'm an old dog seeking new tricks, but only if they ware worth effort.
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Old 12th Aug 2015, 00:44
  #39 (permalink)  
 
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A319 have this problems all the time, and I have seen some A320's also with this issue.

Following unofficial procedures seem to resolve this issue 90% of the time.

1. Reset the ATHR on the FCU, simple OFF / ON
2. Increase the Vapp 2 - 3 kts if seen creeping down towards Vls
3. If neither work, pull selected speed, consider going for managed Speed during final few hundred feet of the approach.

4. If all these above fails, go manual thrust, normally the ATHR reset on the FCU works
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Old 12th Aug 2015, 06:01
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Zenj
Use of ATHR requires 5kts. addition to VLS. Why is that? Obviously it is because the system will let speed go 5kts. less sometime. It is not an issue. It doesn't happen in normal circumstances but when atmospheric conditions are demanding. For stronger winds there is addition from 5kts to 15kts at pilot's discretion. I do share John Smith's confidence in A320 ATHR and GS MINI.
truckflayer's suggestions: First, Non standard method of reengaging ATHR seems harmless enough but I do not know if it really works. Second and third not a good one because it negates GS MINI. Fourth one going manual thrust should be done before 1000ft according to Airbus.
RAT5 There is nothing intuitive for humans in the air. The correct word is habitual from earlier aircraft. Habits can be unlearned or learned. I am sure Airbus designers knew all those points you mention. There is no point fathoming airbus while flying a Boeing non FBW. If you were to fly an airbus for a living you will do it as efficiently as anything else you flew. As the US airways pilot Eric Parks on his airbusdriver.net says "Welcome to Airbus! all resistance is futile,you will be assimilated, "

Last edited by vilas; 12th Aug 2015 at 07:50.
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