Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

ATHR response delay

Tech Log The very best in practical technical discussion on the web

ATHR response delay

Old 12th Nov 2020, 14:03
  #1 (permalink)  
Thread Starter
 
Join Date: May 2008
Location: india
Posts: 123
ATHR response delay

Hello All,
I have been flying Airbus since a long time and have flown CFM IAE and NeO(PW and Leap). Mostly in PW and IAEs, sometimes, I have felt ATHR kicking in very late during flare to maintain Vapp And hence causing late arrest of the sink.
I usually hold the THR LVR at CLB till the sink rate is arrested. Mostly it works but I am afraid where GS is 3.3 or 3.5 and high altitude, might result in a very firm touch down.
Would love to hear views and experiences of other A320 folks.
harsh786techy is offline  
Old 12th Nov 2020, 16:14
  #2 (permalink)  
 
Join Date: Aug 2017
Location: LFPG
Posts: 27
Manual thrust, much easier and more precise control over exactly where you want the thrust, particularly in the flare but also on the approach, especially in any sort of gusty conditions or area's with low level inversions or local changes in winds that can be better anticipated by a human with local knowledge.
EI_DVM is offline  
Old 12th Nov 2020, 17:38
  #3 (permalink)  
 
Join Date: Sep 2016
Location: USA
Posts: 677
Am I understanding right that in a normal Airbus landing, thrust is increased in the flare?
Vessbot is offline  
Old 12th Nov 2020, 18:31
  #4 (permalink)  
 
Join Date: Mar 2006
Location: USA
Posts: 2,152
Originally Posted by Vessbot View Post
Am I understanding right that in a normal Airbus landing, thrust is increased in the flare?
Autothrust is in speed mode, so without retarding the levers, itíll increase to maintain the selected speed.
Check Airman is offline  
Old 13th Nov 2020, 04:46
  #5 (permalink)  
Thread Starter
 
Join Date: May 2008
Location: india
Posts: 123
Absolutely correct. So my query is how often does in other parts of the world Pilots are opting for ATHR disconnection for these purposes. My company policy is to keep on and if disconnection needed( training purposes) must be before 1000 feet as Airbus.
harsh786techy is offline  
Old 13th Nov 2020, 08:00
  #6 (permalink)  
 
Join Date: Mar 2012
Location: Having a margarita on the beach
Age: 49
Posts: 1,960
Originally Posted by harsh786techy View Post
Absolutely correct. So my query is how often does in other parts of the world Pilots are opting for ATHR disconnection for these purposes. My company policy is to keep on and if disconnection needed( training purposes) must be before 1000 feet as Airbus.
in 27 years of A320/A330 I can count probably on one hand the numbers of times I had to disconnect the ATHR due to unsatisfactory performance and/or gusty/windy conditions. Talking about CFM and RR.
95%+ of the time I disconnect is purely for training purposes.
sonicbum is online now  
Old 13th Nov 2020, 10:44
  #7 (permalink)  
 
Join Date: Nov 1999
Location: UK
Posts: 1,715
Very rarely have a problem with FBW A/THR - it is usually excellent* Sometimes, I am deliberately slow in retarding the levers during the flare - if I need to arrest the V/S a bit, and then the A/THR might try to increase thrust to maintain Vapp. But if it does, just bring the levers back to idle.

Airbus say that if the automatics do not provide the required response, take them out and go manual - at any time. During the flare you can easily add thrust or chop thrust if you have to.



*The A330's I flew had "lazy" A/THR on finals which you had to watch, and has been well documented.
Uplinker is offline  
Old 13th Nov 2020, 12:36
  #8 (permalink)  
 
Join Date: Sep 2011
Location: FL390
Posts: 113
I have felt ATHR kicking in very late during flare to maintain Vapp And hence causing late arrest of the sink.
Only a handful of times in six thousand hours on the A320 series have I felt that the autothrust was needed in the flare to arrest the rate of descent. What height are you starting your flare at?
Fursty Ferret is offline  
Old 14th Nov 2020, 06:57
  #9 (permalink)  
Thread Starter
 
Join Date: May 2008
Location: india
Posts: 123
Well, standard flare height is 30 feet but you need to start early in some conditions like high altitude, weight, tail wind etc, or a combination there of.
In our Region of flying, especially Post monsoon, there is a significant difference between direction and magnitude of upper winds which leads to GS mini bringing the aircraft at higher calculated Vapp (or in gusty winds or in case of wind change due diurnal variation). Further as you are going down for flare and landing, matching it with (lower) Vapp leading the N1 demand reducing. This reduction of N1 demand, I believe makes ATHR lazy, has made me hold on to the ATHR for a longer duration waiting to arrest the sink and then chop it to idle. I would say 20% of the times.
I know of people who consistently gives a small check at 50feet or so which wakes the ATHR somehow but results in longer LDAs long flare, in most of the occasions.

harsh786techy is offline  
Old 14th Nov 2020, 08:29
  #10 (permalink)  
 
Join Date: Jul 2006
Location: Somewhere over the rainbow
Posts: 837
Originally Posted by Uplinker View Post

Airbus say that if the automatics do not provide the required response, take them out and go manual - at any time. During the flare you can easily add thrust.
Hello Uplinker, by this do you mean by going above climb detent briefly during flare?
I believe this technique is not recommended anymore by Airbus as far as I know for the A320 family.
From my experience I canít remember a time I felt the need to add power especially in conf 3 and on the one with Sharklets. They tend to glide nicely.
pineteam is offline  
Old 14th Nov 2020, 10:11
  #11 (permalink)  
 
Join Date: Nov 1999
Location: UK
Posts: 1,715
I have never needed to manually add thrust in the flare, but have allowed the A/THR to do it for me on a couple of occasions, and I have manually added thrust at about 500' on a couple of occasions.

There is a video on PPRuNe somewhere of an A320 that did have to manually add thrust in the flare just before retarding the trust levers, and we discussed it then.

There are two ways one can take manual control of thrust. As you say, the "phase advance" method is not now recommended by Airbus, probably because doing so can bring consequences which some pilots are unaware of and could destabilise the approach in the wrong hands.
Uplinker is offline  
Old 14th Nov 2020, 11:18
  #12 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,000
Originally Posted by harsh786techy View Post
Hello All,
I have been flying Airbus since a long time and have flown CFM IAE and NeO(PW and Leap). Mostly in PW and IAEs, sometimes, I have felt ATHR kicking in very late during flare to maintain Vapp And hence causing late arrest of the sink.
I usually hold the THR LVR at CLB till the sink rate is arrested. Mostly it works but I am afraid where GS is 3.3 or 3.5 and high altitude, might result in a very firm touch down.
Would love to hear views and experiences of other A320 folks.
Expecting ATHR to maintain Vapp during flare is not a recommended technique of the A320 or for that matter any aircraft nor is it required. One has to manually flare sufficiently to break the descent and bring thrust to idle. If the Descent doesn't reduce as required then more back stick is used not the thrust. Speed will decrease during flare and touchdown. Landing distance calculation takes into consideration 4% speed decay during flare and 7sec to touchdown from threshold. If you maintain thrust you compromise the calculation. This is what Indian 737 carriers are doing and in monsoon end up in RW excursions.
Safety first Sept 2020 has an article A Focus on the Landing flare

Last edited by vilas; 14th Nov 2020 at 17:57.
vilas is online now  
Old 15th Nov 2020, 00:33
  #13 (permalink)  
 
Join Date: Jul 2010
Location: Asia
Posts: 1,295
It's possible to get out of synch with the autothrust by over controlling. For example, the aircraft sinks slightly and you over correct by applying too much back pressure.The A/T kicks in and you start going above the profile, you apply forward sidestick and the power comes off. As you get back onto the profile you apply back pressure and the A/T comes in again causing you to climb etc etc.

Small corrections and anticipating slightly will usually cure this, but as stated earlier, if the automatics aren't doing a proper job then disconnect them and fly manually.
krismiler is offline  
Old 15th Nov 2020, 06:55
  #14 (permalink)  
 
Join Date: Jul 2006
Location: Somewhere over the rainbow
Posts: 837
I have seen some guys chasing aggressively the papi even below 100 feet from touchdown resulting in high thrust variations and sketchy landings. From what I have learned, below 100 feet do not chase the papi: Accept what you have even if the Papi says you are slightly too high or too low, at this stage it’s too late. Keep the same pitch and constant ROD around 600/700 feet/min; By doing so the thrust is constant and a safe landing is pretty much guarantied. Many times I have seen skippers trying to be perfectly 2 white 2 red until touchdown and ended landing far due to over controlling and high thrust variations during flare.
pineteam is offline  
Old 15th Nov 2020, 16:36
  #15 (permalink)  
 
Join Date: Mar 2006
Location: USA
Posts: 2,152
Originally Posted by harsh786techy View Post
Hello All,
I have been flying Airbus since a long time and have flown CFM IAE and NeO(PW and Leap). Mostly in PW and IAEs, sometimes, I have felt ATHR kicking in very late during flare to maintain Vapp And hence causing late arrest of the sink.
I usually hold the THR LVR at CLB till the sink rate is arrested. Mostly it works but I am afraid where GS is 3.3 or 3.5 and high altitude, might result in a very firm touch down.
Would love to hear views and experiences of other A320 folks.
If you know that a particular approach is tricky, why not just turn it off? Seems easier than trying to figure it out during the flare.
Check Airman is offline  
Old 16th Nov 2020, 05:57
  #16 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,000
The OP has a technique that after flare he waits till thrust comes up before reducing it to idle. As I posted before this incorrect and not supported in any document. With ATHR on when you flare you are supposed to close thrust and not wait till thrust comes up to maintain speed. It is the flare that is supposed to reduce ROD and not the thrust. If GS mini effect had increased Vapp then you may reach the flare height with idle thrust. Any aircraft can be landed with idle thrust if speed is high(within stabilized criteria). During flare if more thrust is required to reduce the sink then the approach is unstable and GA should be executed. And yes! Approach can become unstable even at flare height.
vilas is online now  
Old 16th Nov 2020, 06:15
  #17 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,000
Was this required? This was an unstabilized approach. A GA would have prevented the nightmare. From the latest safety first.

​​​​​​CASE STUDY 1: BOUNCED LANDING, NOSE LANDING GEAR IMPACT, AND A TAIL STRIKE ON GO-AROUNDEvent Description

An A320 was on the final approach segment of its ILS approach, configured for landing (CONF FULL).

The Pilot Flying (PF) disconnected the autopilot at 370 ft Radio Altitude (RA) and kept autothrust ON. At 200 ft, tailwind variations caused the airspeed to drop below approach speed (Vapp).

From 100 ft RA and below, high tailwind gradients maintained the airspeed below Vapp -5 kt despite autothrust increase and reached a minimum of 119 kt (Vapp -20 kt) at 5 ft RA.

The PF performed the flare at 14 ft and at the same time started to slowly push the thrust levers above CLB detent.

The aircraft touched down on its main landing gear and bounced. During the bounce, a PITCH PITCH auto callout triggered.

The PF applied full nose down order and retarded the thrust levers to IDLE. This triggered an extension of ground spoilers leading the aircraft to heavily impact the runway , first with its nose landing gear and then its main landing gear.

The impact of the nose gear resulted in another sudden increase of the aircraftís pitch and the PITCH PITCH auto callout triggered for a second time. The PF initiated a go-around by setting TOGA thrust and applying a full nose up command. There was a tail strike as the aircraft lifted off from the runway at 133 kt.

The NLG wheels separated due to the impact of the NLG on the runway and one wheel was sucked into Engine 1, causing this engine to stall. Other system failures occurred due to the impact on the NLG and these caused the aircraft to revert to alternate law. The flight crew diverted to a different airport and eventually landed the aircraft.

Last edited by vilas; 16th Nov 2020 at 06:28.
vilas is online now  
Old 16th Nov 2020, 06:30
  #18 (permalink)  
 
Join Date: Jul 2006
Location: Somewhere over the rainbow
Posts: 837
I remember that incident; It happened in Macau.
Waiting 370 feet to disconnect the AP... SMH
And no it’s was not LVO.
pineteam is offline  
Old 16th Nov 2020, 08:32
  #19 (permalink)  
 
Join Date: Nov 1999
Location: UK
Posts: 1,715
Good grief !

Full nose down order following a bounce........Full nose up order while still on the runway......

Who on Earth taught that pilot how to fly FBW with a side-stick?

Who on Earth taught that pilot what to do following a bounce?

(Hint: obviously nobody).
Uplinker is offline  
Old 16th Nov 2020, 09:55
  #20 (permalink)  
 
Join Date: Feb 2001
Location: UK
Posts: 118
Surely for Performance A aircraft the defined Vref for the approach (which may have an increment added to establish a Vapp speed) would only ever apply down to the screen height of 50ft.The Vapp speed for the A320 already includes an increment for the autothrust which doesn't apply for manual thrust approaches. This increment (when applied) is allowed for in the performance calculation for landing distance. In practice we rarely choose to fly Vref at the screen height when manual thrust flyiing.

An over fixation of maintaining speed (Vapp or Vref) below the screen height isn't in keeping with the requirements of a Perf A aircraft.

The certification of the aircraft would include a consideration of the speed/handling characteristics of the aircraft throughout the range of conditions likely to be encountered and would as such influence the handling advice to pilots, in particular below the screen height. In the A320 series that advice is to prioritise attitude and sink rate during the flare and landing sequence and not speed. Both of these are "eyes out" tasks. If Vapp (or Vref) is not achieved at the screen height, or the aircraft is experiencing rapid changes of speed/thrust then the aircraft is potentially unstable and a go-around or baulked landing might be best considered.

I'm an average pilot on my best days. I have to say when conditions make speed control a challenge I don't rate my ability to control speed more accurately than the autothrust. Whilst I'm more than confident to do so when required I've never had that little confidence in the autothrust function.

Airbus have an extremely competent flight test team and certification process. Follow their advice. To formulate alternative practice on the cuff would seem risky.
a5in_the_sim is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.