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757 pilot had history of hairy landings

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757 pilot had history of hairy landings

Old 3rd Sep 2020, 08:51
  #81 (permalink)  
 
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Originally Posted by Bus Driver Man View Post
Yes, but GS Mini minimises the need for big thrust changes.
A positive gust increases your IAS, but the Vapp target increases as well. Only a small thrust increase should be required to compensate for the extra headwind.
A negative gust decreases your IAS, but the Vapp target decreases as well.

I think that misd-agin is referring to the A/THR overcorrecting in gusty conditions. Which it does. With the risk of reducing or adding too much power just before or during the flare.
I must have been lucky then because in 13 years of flying A320/321 and A330, I don't remember ever seeing the auto-thrust overreact; it follows the speed bug. (I have seen it very busy on A320/321 and also had it under-react on A330). And I have landed in extremely gusty conditions seconds away from going around on several occasions because I had almost run out of roll authority.

The point of groundspeed mini is that it maintains the energy of the aircraft. If the headwind blows harder, the engines push harder, which maintains the energy, (and the groundspeed). This is completely opposite to a Boeing, which maintains the IAS, and would reduce thrust with a headwind gust. But one should not apply one type's SOP in the other.

I am very wary of pilots who pull for speed or use manual thrust to override Airbus ground speed mini. (Not saying you do).
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Old 3rd Sep 2020, 10:49
  #82 (permalink)  
 
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Originally Posted by Uplinker View Post
I am very wary of pilots who pull for speed or use manual thrust to override Airbus ground speed mini. (Not saying you do).
Agreed. Often it is due to a lack of understanding of the system. A quick point at the groundspeed provides comfort even if the speedtape looks a bit wrong.

There should never be any need to speed intervene unless GS-mini is getting towards the flap overspeed limit (even then, briefly pull speed and go back to managed speed as the wind starts to drop off as you get closer to the ground). Providing your IFLD permits it, these gusty sorts of days are great for flap 3. It gives you a few extra knots on the flap limiting speed, helps the aircraft settle onto the runway and gives you more performance in the go around.

champ
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Old 3rd Sep 2020, 14:16
  #83 (permalink)  
 
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There should never be any need to speed intervene unless GS-mini is getting towards the flap overspeed limit (even then, briefly pull speed and go back to managed speed as the wind starts to drop off as you get closer to the ground). Providing your IFLD permits it, these gusty sorts of days are great for flap 3. It gives you a few extra knots on the flap limiting speed, helps the aircraft settle onto the runway and gives you more performance in the go around
Agreed with the first statement. There's no need to even momentarily go select because the GS mini limitation on IAS with full flap is VFE-5 and as the speed trend goes to VFE ATHR will head towards idle. Even select speed can't do more GSmini IAS limits are VFE-5 in full and VFENext for other configurations. So in Flap3 the IAS limit is 177kts. i.e. 8kts less than VFE of 185kts.
​and in Flaps full it is 5kts from VFE. but aircaft will find it easier to accelerate in Flap3 than Flap full. So not much advantage. Besides in turbulence for better handling Air bus recommends Flaps Full not Flap3 unless windsheer is expected.

Last edited by vilas; 3rd Sep 2020 at 16:06.
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Old 3rd Sep 2020, 22:42
  #84 (permalink)  
 
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Originally Posted by vilas View Post
GSmini IAS limits are VFE-5 in full and VFENext for other configurations. So in Flap3 the IAS limit is 177kts. i.e. 8kts less than VFE of 185kts.
​and in Flaps full it is 5kts from VFE. ...
Hey Vilas,

This GSmini limitation, ďand VFE Next for other configurations.Ē isn't in our manual. (we donít use the FCOM) can you post the excerpt of that so I can take it back to our folks?

thanks,






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Old 4th Sep 2020, 04:03
  #85 (permalink)  
 
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Originally Posted by CaptainMongo View Post
Hey Vilas,
This GSmini limitation, ďand VFE Next for other configurations.Ē isn't in our manual. (we donít use the FCOM) can you post the excerpt of that so I can take it back to our folks?
thanks,
Hi


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Old 5th Sep 2020, 01:05
  #86 (permalink)  
 
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Originally Posted by Uplinker View Post
I must have been lucky then because in 13 years of flying A320/321 and A330, I don't remember ever seeing the auto-thrust overreact; it follows the speed bug. (I have seen it very busy on A320/321 and also had it under-react on A330). And I have landed in extremely gusty conditions seconds away from going around on several occasions because I had almost run out of roll authority.
Iím not sure if itís due to the IAE engines, or if itís a software modification on newer A320s, but Iíve noticed an occasional late A/THR reaction followed by an overcompensation. E.g idle thrust kept until manoeuvring speed - 5kts or Vapp - 5kts, followed by an excessive thrust increase resulting in exceeding the target speed before finally stabilising at the correct speed. Iíve even had it a few times during the flare resulting in a loss of energy or excess energy. Iíve never seen this with CFM engines, or even older aircraft with IAE engines. Hence my preference for manual thrust in gusty conditions. Could slow A/THR response be the result of a software modification? Itís even noticeable when selecting open climb: after the engines have already spooled up, selecting a lower speed to increase the climb rate will initially result in a thrust reduction by the A/THR before increasing it back to CLB thrust. Again, I have never seen this on CFM engines.
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Old 5th Sep 2020, 01:27
  #87 (permalink)  
 
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Originally Posted by Uplinker View Post
I am very wary of pilots who pull for speed or use manual thrust to override Airbus ground speed mini. (Not saying you do).
Completely agree. GS Mini is designed for a reason.
The only issue, and itís quite rare, is that configuring might be difficult with a high target speed. It feels more comfortable to temporarily reduce the speed with a few knots before selecting the next flaps if the target speed was exactly VFE next.

Interesting to know is that the GS mini factor is different on other Airbus models compared to the A320CEO, eliminating a possible target speed close to VFE:Why is there a different Ďkí factor for ground speed mini depending on the aircraft model?

The factor of 1 used on A320ceo aircraft could not be used for the other aircraft models due to differences of their deceleration capability. The A320ceo has a stronger deceleration capability when compared to A320neo, A330/A340 family aircraft, A350 and A380 aircraft.

In the case of a strong ground effect, a lower deceleration capability may lead to an excessive speed at flare. For example, a 20kt headwind at 200ft that reduces to 5kt on ground (corresponding to the 5kt tower headwind inserted in FMS PERF APPR page), a factor of 1 requires a deceleration of 15kt to reach VAPP. With a k value of 0.33, the aircraft only needs to decelerate by 5kt to compensate its lower deceleration capability. It reduces the risk of excessive speed at flare. The drawback is that there is a slight increase in thrust variations in gusty conditions, since the speed increment will not be sufficient to counteract the IAS increase due to a gust. The best overall compromise was demonstrated to be a 0.33 factor.

(Airbus Safety First July 2017)


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Old 5th Sep 2020, 02:00
  #88 (permalink)  

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I can see the 757 being a handful for an inexperienced pilot, but it is not a difficult plane to fly, or to land.
I needed an extra sector in the 757 as well, but we trained in the 767-200 and 767-300 every other sector, they each fly a bit different.
(probably had 35-40 hours total line training, the last flight from Boston a day or two before 9/11, same type and same airline that got hijacked and flew into the World Trade Center. )
Anybody needing a ridiculous amount of line training to land a 757 should find a different profession, it is not an SR-71 or some other exotic machine, lots or rudder and aileron/elevator control.
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Old 5th Sep 2020, 09:30
  #89 (permalink)  
 
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@Bus Driver Man

Depends what you mean by speed. The far superior Airbus groundspeed mini system will absolutely nail your groundspeed. And ground speed is of course what is important when landing, (as long as it keeps within sensible IAS limits, which it does).

As far as energy, well the ground speed mini system preserves energy, so even if the engines briefly reduce towards idle, the aircraft energy will be preserved, so no bad things should happen.

SOPs require the engines to be spooled up at 1000', and on gusty days with groundspeed mini there is a chance they might happen to be briefly at flight idle at this point. Personally, I am happy knowing the energy is preserved.

If the engines spool up massively just as you flare; they will be doing so to regain Vgs mini and preserve the energy, but if you think it is a problem you can just bring the thrust levers back out of the CLB detent early to limit this before pulling them all the way back to idle.

Your slowly reacting auto-thrust - don't know, but Airbus do consider the passenger comfort, so probably auto-thrust is programmed to be "gentle" while staying within flight limits. This might also be why some pilots think auto-thrust "overreacts", since on a gusty approach, it has to nail the groundspeed mini and cannot be gentle for that phase. So to those pilots, perhaps it suddenly seems a bit manic?

The older A330s I flew had 'lazy' auto-thrust in the lower levels, and I used phase advance (no longer approved) on a couple of occasions to keep the speed above Vapp-5

@Tower Dog. I agree. Years ago while still training, I once blagged a flight in a 757 FFS, having flown nothing larger or more complicated than a Seneca at that time. I was able to take off, fly a circuit and land, (fully manual everything), reasonably OK

Last edited by Uplinker; 5th Sep 2020 at 09:51.
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Old 5th Sep 2020, 11:40
  #90 (permalink)  
 
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Originally Posted by Uplinker View Post
@Bus Driver Man
Depends what you mean by speed. The far superior Airbus groundspeed mini system will absolutely nail your groundspeed. And ground speed is of course what is important when landing, (as long as it keeps within sensible IAS limits, which it does).
As far as energy, well the ground speed mini system preserves energy, so even if the engines briefly reduce towards idle, the aircraft energy will be preserved, so no bad things should happen.

SOPs require the engines to be spooled up at 1000', and on gusty days with groundspeed mini there is a chance they might happen to be briefly at flight idle at this point. Personally, I am happy knowing the energy is preserved.

If the engines spool up massively just as you flare; they will be doing so to regain Vgs mini and preserve the energy, but if you think it is a problem you can just bring the thrust levers back out of the CLB detent early to limit this before pulling them all the way back to idle.

Your slowly reacting auto-thrust - don't know, but Airbus do consider the passenger comfort, so probably auto-thrust is programmed to be "gentle" while staying within flight limits. This might also be why some pilots think auto-thrust "overreacts", since on a gusty approach, it has to nail the groundspeed mini and cannot be gentle for that phase. So to those pilots, perhaps it suddenly seems a bit manic?

The older A330s I flew had 'lazy' auto-thrust in the lower levels, and I used phase advance (no longer approved) on a couple of occasions to keep the speed above Vapp-5

@Tower Dog. I agree. Years ago while still training, I once blagged a flight in a 757 FFS, having flown nothing larger or more complicated than a Seneca at that time. I was able to take off, fly a circuit and land, (fully manual everything), reasonably OK
Chances of engines remaining spooled up are good in GSmini. Because its maintaining higher IAS in response to gust. Also the feature AB Approach ATHR is designed to be more responsive to speed variations below 3200ft. If very gusty conditions are expected it is better to add 5 to 15kts speed addition as permitted. I am a firm believer in taking manufacturer's opinion before trying something non standard. The are quick to respond.
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Old 5th Sep 2020, 15:58
  #91 (permalink)  

Only half a speed-brake
 
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Originally Posted by Bus Driver Man View Post
Itís even noticeable when selecting open climb: after the engines have already spooled up, selecting a lower speed to increase the climb rate will initially result in a thrust reduction by the A/THR before increasing it back to CLB thrust. Again, I have never seen this on CFM engines.
It most certainly happens with old CFMs too.

Courtesy of fellow PPRuNers, you will find the technical explanation here if digging deep enough.
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Old 5th Sep 2020, 17:18
  #92 (permalink)  
 
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This is what I posted in 2019
The following information was released by Airbus in Sochi crash investigation:
The logic of integration of the autopilot/flight director (AP/FD) pitch control and the
autothrust control
¨If AP/FD pitch mode controls a vertical trajectory (e.g. V/S, ALT), then AT controls speed.
¨If AP/FD pitch mode controls a speed (e.g. OPCLB), then AT controls thrust.
¨If no AP/FD pitch mode is engaged, then АТ controls speed.
Logic sequence of the OPEN CLB mode
¨for level change more than 1200 ft:
¨at OPEN CLB mode engagement by the pilot, V/S control with V/S target = +8000 ft/min (40 m/s) is applied for AP/FD, and SPEED/MACH mode is engaged for AT
¨when engine N1 reaches 95% N1CLB mode, AP/FD switches to SPEED/MACH control law, whereas AT switches to the THRUST mode
¨Throughout this time the FMA displays THR CLB for AT and OPCLB for AP/FD
The given scheme of engagement for the OPEN CLB mode ensures the uniformity of the aircraft response in all configurations and within the whole range of the flight altitudes and speeds.
¨For level change less than 1200 ft:
¨at OPEN CLB mode engagement by the pilot, V/S control with V/S target = + 1000 ft/min (5 m/s) is applied for AP/FD, and SPEED/MACH mode is engaged for AT
¨ Throughout this time FMA displays THR CLB for AT and OPCLB for AP/FD
In this case the climb is in fact performed in the vertical speed control mode.
***
It should also be noted that if the OPEN CLB mode is engaged less than 30 seconds after the aircraft level off function is activated, the autopilot is authorized to use the vertical acceleration at the maximum value of 0.3g, whereas usually it is only 0.15g.
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Old 5th Sep 2020, 18:26
  #93 (permalink)  

Only half a speed-brake
 
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In simple terms:

After activating OP CLB, if you dial back (or manage down) the speed for zoom climb BEFORE N1 would spool to +95 N1, the A/THR is still active and will follow the slower target by reducing thrust.

Ce n'est pas un bug mais une fonctionnalitť.

More regrettably, this is another thread hijacked by the Airbus borg brigade. In my defence, I have no choice.
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