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Pacific
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Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 2:55 pm

I have just taken a return flight on an airline and both trips were on the A321 with sharklets. Both landings were in good weather conditions, one at night, the other during the day.

On both occasions, we seemed to come in normally, engine power and decent rate seemed stable throughout the whole approach. As we were low over the runway around when engines are reduced to idle in most of my previous flights, there was a very noticeable application of power, and the aircraft noticeably accelerated. The application of power also reduced the descent rate and then, the pilot finally idled the engines. We touched down while the engines were still spooling down to idle.

From my limited understanding, I thought the engines are reduced to idle (or "RETARD" as the Airbus GPWS would call out) at around 30 feet AGL and the flare is responsible for reducing the descent rate. Please enlighten a nervous flyer.  
 
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zeke
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 5:03 pm

Quoting Pacific (Thread starter):
On both occasions, we seemed to come in normally, engine power and decent rate seemed stable throughout the whole approach. As we were low over the runway around when engines are reduced to idle in most of my previous flights, there was a very noticeable application of power, and the aircraft noticeably accelerated. The application of power also reduced the descent rate and then, the pilot finally idled the engines. We touched down while the engines were still spooling down to idle.

Thats due to a very low level wind change, the pilots would have seen the speed drop back in the flare (or just before), you add thrust to maintain speed and compete the landing. Not doing so can result in a very heavy landing, bounce, or even a gear change.

Nothing unique to the aircraft type, pretty common technique needed in NRT, TPE, HKG & KUL.
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mmo
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 5:12 pm

Quoting Pacific (Thread starter):
From my limited understanding, I thought the engines are reduced to idle (or "RETARD" as the Airbus GPWS would call out) at around 30 feet AGL and the flare is responsible for reducing the descent rate. Please enlighten a nervous flyer.

Could be several things. While I agree with what Zeke wrote, I would also offer a couple of other observations.

First of all, one could argue if you do hear "retard" you have not started the thrust reduction early enough. The "retard" call is not a command but a reminder you failed to do just that.

The second thing could have been a loss of energy prior to thrust reduction which then the auto throttles dis what they were designed to do and added thrust to compensate for the loss of energy. The other thing that could have happened is the thrust reduction was already underway and the pilots observed/felt a loss of energy and manually added thrust. Either way, there is nothing to worry about as it was a perfectly normal landing. If you are asking about if it's a 321 thing, then I would also say no. But, the 321 does land differently that the 320/319.
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AIRWALK
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 5:19 pm

A sudden reduction in a headwind component may be responsible for that, it can reduce the indicated airspeed, resulting in an increased sink rate which must be countered with thrust as it would be too late to pitch down.

Quoting Pacific (Thread starter):
and the flare is responsible for reducing the descent rate

Depends what you mean by flare. On a descent, pitch primarily controls airspeed and thrust primarily controls ROD. If you mean round out then yes it is to break the ROD, however the hold off period is done to decay airspeed. If the aircraft was too slow, a heavy landing would occur, thrust would be required to prevent this.
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barney captain
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 5:21 pm

Quoting mmo (Reply 2):
First of all, one could argue if you do hear "retard" you have not started the thrust reduction early enough. The "retard" call is not a command but a reminder you failed to do just that.

Interesting, I never knew that. Every time I've ridden up front on an AB I've heard that call out, I just assumed it happened on every landing.
Southeast Of Disorder
 
INFINITI329
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 5:30 pm

I have noticed this with Q400 landing at MDW & YTZ, right before touchdown power is added
 
AF1624
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 6:10 pm

Quoting infiniti329 (Reply 5):
I have noticed this with Q400 landing at MDW & YTZ, right before touchdown power is added

Are you sure that this is power being added?

On the Q400, the Prop speed changes when the aircraft goes to final approach: to be ready in case of a go around, and altogether to have the appropriate propeller pitch for beta mode and reverse on the ground, the prop RPM goes from 800rpm (which is a cruise setting) to 1000rpm (which is the take off/go around setting).

That prop speed/pitch change results in a significant increase in noise.

Basically think of it like a car shifting to a lower gear - more RPM, more "aggressiveness" or "reactivity" (as in capacity to accelerate or decelerate), but much less top speed.
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hivue
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 6:44 pm

Quoting mmo (Reply 2):
The "retard" call is not a command but a reminder you failed to do just that.

Then every AB landing flight deck video I've ever seen on youtube the pilot has not started thrust reduction early enough.
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bueb0g
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 7:41 pm

Quoting mmo (Reply 2):
First of all, one could argue if you do hear "retard" you have not started the thrust reduction early enough. The "retard" call is not a command but a reminder you failed to do just that.

Are you sure that's the case? Even if the thrust levers are already at idle, you will get a "retard" call just after 20 ft.

Quoting hivue (Reply 7):
Then every AB landing flight deck video I've ever seen on youtube the pilot has not started thrust reduction early enough.
www.youtube.com/rodrigodavid appears to normally to go idle at 100ft. Could be because he's often landing at airfields with shorter runways.
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mmo
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 7:42 pm

Quoting hivue (Reply 7):
Then every AB landing flight deck video I've ever seen on youtube the pilot has not started thrust reduction early enough.

Obviously, you seem to think I am wrong. Here it is from the FCTM:

2) THRUST LEVERS SET TO IDLE
If thrust levers are set to IDLE, A/THR is set to off. This technique is usually
used in descent, when the A/THR is in THR IDLE, or at landing. During flare,
with the A/THR active, the thrust levers are set to the CLB detent. Then, when
thrust reduction is required for landing, the thrust levers should be moved
smoothly and set to the IDLE stop. This will retard thrust, and set A/THR to off.
As a reminder, the "RETARD" aural alert will sound. In flare, this aural alert will
occur at 20 feet, except in the case of autoland, where it occurs at 10 feet.
It should be noted that, when the thrust levers are set back to IDLE and A/THR
set to off: The A/THR can be reactivated by pressing the pushbutton on the
FCU, and returning the thrust levers to the applicable detent. The thrust levers
should be immediately returned to the applicable.



If you are reducing the thrust to idle at 20' , it's probably a little too late. Notice the verbage that states "AS A REMINDER, THE "RETARD" AURAL ALERT WILL SOUND." So, YES, every video you have watched is displaying a late power reduction.
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hivue
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 7:55 pm

Quoting mmo (Reply 9):

OK thanks. So what you meant to say was "The 'retard' call is not a command but a reminder in case you failed to do just that."
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
mmo
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 7:58 pm

Quoting hivue (Reply 10):
OK thanks. So what you meant to say was "The 'retard' call is not a command but a reminder in case you failed to do just that."
Quoting mmo (Reply 2):
First of all, one could argue if you do hear "retard" you have not started the thrust reduction early enough. The "retard" call is not a command but a reminder you failed to do just that.

I think you will find that is exactly what I said.
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AIRWALK
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 8:05 pm

Quoting hivue (Reply 10):
The 'retard' call is not a command but a reminder in case you failed to do just that.

Correct, but If I am not mistaken, in regard to an autoland operation, the retard call is in fact a command.
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barney captain
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 8:09 pm

Quoting mmo (Reply 11):
I think you will find that is exactly what I said.

I sure didn't interpret what you wrote that way.

Quoting mmo (Reply 2):
First of all, one could argue if you do hear "retard" you have not started the thrust reduction early enough. The "retard" call is not a command but a reminder you failed to do just that.

"If you hear it" certainly reads as though the call out may not happen if thrust is reduced early enough.

So call out always happens. Got it.
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mmo
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 8:42 pm

Quoting AIRWALK (Reply 12):
Correct, but If I am not mistaken, in regard to an autoland operation, the retard call is in fact a command.

On an autoland the "retard" command is at 10' (RA) and correct, it is a command.

Quoting barney captain (Reply 13):
"If you hear it" certainly reads as though the call out may not happen if thrust is reduced early enough.

So call out always happens. Got it.

Actually, if you retard the T/L before 30' you will not hear the "retard" command
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bueb0g
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 10:11 pm

Quoting mmo (Reply 14):
Actually, if you retard the T/L before 30' you will not hear the "retard" command

Do you mean the autoland 10' retard command, or the manual landing 20' retard 'reminder?' I believe Barney was talking about the reminder rather than the command. I don't know how it is with autoland, but with a manual landing, it doesn't matter what height you retard the thrust levers, you will still get the callout.

Evidence:

https://www.youtube.com/watch?v=mhVUcub65Ts
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mmo
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 10:23 pm

Quoting bueb0g (Reply 15):
Do you mean the autoland 10' retard command, or the manual landing 20' retard 'reminder?' I believe Barney was talking about the reminder rather than the command. I don't know how it is with autoland, but with a manual landing, it doesn't matter what height you retard the thrust levers, you will still get the callout.

On an auto land the "retard" callout occurs at 10' (RA). It is a command and should be briefed in the approach review since it is very different than normal ops.

With respect to the "retard" in non auto land conditions, the FCOMS I have indicate you will not get the callout if the T/L is in the idle position. While I only have about 1500 hours in the 320 family, I can assure you I have not heard retard during each and every landing.
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bueb0g
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RE: Applying Thrust Just Before Touchdown - A321

Mon Jan 26, 2015 10:35 pm

Quoting mmo (Reply 16):
With respect to the "retard" in non auto land conditions, the FCOMS I have indicate you will not get the callout if the T/L is in the idle position. While I only have about 1500 hours in the 320 family, I can assure you I have not heard retard during each and every landing.

Strange. Maybe a software update on recent builds? The channel of the video I linked, which is run by an Avianca Brasil A320 captain, has several videos where the T/L are retarded to idle at around 100 feet and there is still a 20' retard callout.
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AF1624
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RE: Applying Thrust Just Before Touchdown - A321

Tue Jan 27, 2015 6:30 am

Quoting bueb0g (Reply 17):

Yes, I have seen that behaviour also. As far as I know the retard call-out always happens, just at different heights depending on the type of approach.

Maybe this is a customer option?
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YYZatcboy
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RE: Applying Thrust Just Before Touchdown - A321

Tue Jan 27, 2015 8:23 am

Quoting AF1624 (Reply 6):
On the Q400, the Prop speed changes when the aircraft goes to final approach: to be ready in case of a go around, and altogether to have the appropriate propeller pitch for beta mode and reverse on the ground, the prop RPM goes from 800rpm (which is a cruise setting) to 1000rpm (which is the take off/go around setting).

Thats wrong. They hit the RED NP button which arms the props to 1020RPM in the event the torque goes above 50%. However if it does not as in most normal landings the props stay at 850 RPM.
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AF1624
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RE: Applying Thrust Just Before Touchdown - A321

Tue Jan 27, 2015 9:47 am

Quoting YYZatcboy (Reply 19):
Thats wrong. They hit the RED NP button which arms the props to 1020RPM in the event the torque goes above 50%. However if it does not as in most normal landings the props stay at 850 RPM.

Ah? Thanks for the correction. I could have sworn that this was the reason for the noise increase on approach...
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Rara
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RE: Applying Thrust Just Before Touchdown - A321

Tue Jan 27, 2015 5:41 pm

Quoting mmo (Reply 9):
If you are reducing the thrust to idle at 20' , it's probably a little too late. Notice the verbage that states "AS A REMINDER, THE "RETARD" AURAL ALERT WILL SOUND." So, YES, every video you have watched is displaying a late power reduction.

The "retard" aural alert will sound with every landing, no matter when the thrust is reduced. It doesn't say anything else in the FCOM. It if keeps on sounding, you have reduced power too late (thus the saying "the third 'retard' is meant as an insult").

Perhaps in a few isolated cases, the "retard" callout may be blocked out by another signal or altitude callout, but that would be very rare indeed. I'd be interested whether there was a video or something documenting it.
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vikkyvik
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RE: Applying Thrust Just Before Touchdown - A321

Tue Jan 27, 2015 7:11 pm

Quoting Pacific (Thread starter):
and the aircraft noticeably accelerated

Just as a general comment, it can also be very difficult to judge acceleration changes and such as a passenger sitting in the cabin. A good example is that falling feeling you sometimes get soon after takeoff, when thrust is pulled back to climb thrust and flaps are retracted. Always feels like you're falling toward the ground, when you're actually just reducing your upward acceleration, and climbing at a decreased rate.

Quoting mmo (Reply 2):
The second thing could have been a loss of energy prior to thrust reduction which then the auto throttles dis what they were designed to do and added thrust to compensate for the loss of energy. The other thing that could have happened is the thrust reduction was already underway and the pilots observed/felt a loss of energy and manually added thrust.

Not sure how this is different to what Zeke wrote. A sudden headwind decrease / tailwind increase is equivalent to an energy loss.
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longhauler
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RE: Applying Thrust Just Before Touchdown - A321

Tue Jan 27, 2015 8:38 pm

It depends on whether you have an MDA or a DH set in the FMGC for the approach.

If you have an MDA set (height above sea level), then the autothrust system assumes a manual landing. It doesn't have to be, you can autoland on an ILS with an MDA set, (in fact CAT I ILSs are done this way). But ... during the flare and landing, the autothrust system will try to maintain Vapp. It is a "trick" to get a smoother landing, as the thrust comes up just before touchdown. For the record, this is not the way Airbus intends the aircraft to be landed.

In this case, the "Retard" call is a commad to bring the thrust back to idle, as it is required for landing. (Otherwise the thrust will keep coming up, trying to maintain Vapp).

If you have a DH set, (radio altitude), then autothrust system assumes an automatic landing. This must be set this way for any CAT II or CAT III landing. (everywhere except in SEA!)

With a DH set, then the autothrust system will start to bring the thrust toward idle during the flare and touchdown, regardless of thrust lever position. The "retard" call is now a reminder to match the thrust levers with the now actual thrust setting.

In both cases, DH and MDA, bringing the thrust levers to idle disconnects the autothrust system.
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hivue
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RE: Applying Thrust Just Before Touchdown - A321

Tue Jan 27, 2015 9:08 pm

Quoting longhauler (Reply 23):
The "retard" call is now a reminder to match the thrust levers with the now actual thrust setting.

So is that why the phrasing is the general "Retard" rather than the specific "Throttles to idle" or something like that.
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longhauler
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RE: Applying Thrust Just Before Touchdown - A321

Tue Jan 27, 2015 10:32 pm

Quoting hivue (Reply 24):
So is that why the phrasing is the general "Retard" rather than the specific "Throttles to idle" or something like that.

Yes, with the A/P engaged, with the A/T active, the thrust will come back to idle during the flare. The "retard" call reminds you to bring the thrust levers back to match the actual thrust, (and disconnect the A/T system).

With the A/P disengaged during the flare, the A/T system will try to maintain Vapp. The "retard" call, now is a command, as otherwise the aircraft would never go below Vapp.

The Airbus cockpit is very elegant in it's subtleties ... this being one of them. "Throttles (or thrust levers) to idle" would work in both cases, but "retard" is just more elegant, and simple. But ... you have say it when a French accent.   It is reTARD, not REtard!
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hivue
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RE: Applying Thrust Just Before Touchdown - A321

Tue Jan 27, 2015 10:37 pm

Quoting longhauler (Reply 25):
But ... you have say it when a French accent. It is reTARD, not REtard!

   All the RA callouts on AB aircraft should be in a French accent.  
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FlightShadow
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RE: Applying Thrust Just Before Touchdown - A321

Wed Jan 28, 2015 4:10 am

Quoting Pacific (Thread starter):
low over the runway around when engines are reduced to idle in most of my previous flights, there was a very noticeable application of power

Surprised nobody has yet suggested your pilots may have simply been former naval aviators 
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tommy1808
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RE: Applying Thrust Just Before Touchdown - A321

Wed Jan 28, 2015 9:29 am

Quoting FlightShadow (Reply 27):
Surprised nobody has yet suggested your pilots may have simply been former naval aviators

always aiming for the spot where the no. 3 wire would be?

best regards
Thomas
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Starlionblue
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RE: Applying Thrust Just Before Touchdown - A321

Wed Jan 28, 2015 10:04 am

Quoting tommy1808 (Reply 28):

Quoting FlightShadow (Reply 27):
Surprised nobody has yet suggested your pilots may have simply been former naval aviators

always aiming for the spot where the no. 3 wire would be?

I think Flightshadow meant that pushing the throttles full forward on touchdown is normal practice in arrested landings. If you catch a wires, the plane is going to stop anyway. If you don't catch the wires, you'll need that power to go around. No time to wait for the engines to spool up.
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Pacific
Topic Author
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RE: Applying Thrust Just Before Touchdown - A321

Wed Jan 28, 2015 11:15 am

Thanks for all the replies. This is some very facinating insight into landing techniques and the intricacies of the Airbus cockpit.

P.s. I was on Philippine Airlines.
 
FlightShadow
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RE: Applying Thrust Just Before Touchdown - A321

Thu Jan 29, 2015 5:51 am

Quoting Starlionblue (Reply 29):

  
"When the tide goes out, you can tell who was skinnydipping."
 
tommy1808
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RE: Applying Thrust Just Before Touchdown - A321

Thu Jan 29, 2015 7:16 am

Quoting Starlionblue (Reply 29):
I think Flightshadow meant that pushing the throttles full forward on touchdown is normal practice in arrested landings.

I know, I was joking. And i just worked my way through the Jake Grafton series ....lol

best regards
Thomas
Well, there is prophecy in the bible after all: 2 Timothy 3:1-6

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