NW A320 tailstrike at DEN, possible W/O?

[Sleeping Freight Dog]

Looks like NW had a rough landing at DEN resulting in a tail strike on
an A320 and possible W/O of the aircraft.
Pretty hard landing with a 3.G+ force applied
JACDEC - Current News (http://www.jacdec.de/news/news.htm)

[ready eddy]

Eh, the report says it's a DC10, how did you make it out to be an A320????

[11Fan]

Try scrolling down. It's the third one, at least for the moment.

[pattern_is_full]

Ready Eddy: read down two events - May 5.

NW incident doesn't appear to have made Denver local media.

DC-10 hard landing has its own thread...

[herkman]

3.5 G landing, things may have changed, but we were taught in the Air Force, that G meters do not read correctly on the ground.

Is that still the case.

Regards

Col

[PlatinumFlyer]

Accident: Northwest A320 at Denver on May 4th 2009, tail strike on landing (http://avherald.com/h?article=41951d02)

[lomapaseo]

3.5 G landing, things may have changed, but we were taught in the Air Force, that G meters do not read correctly on the ground.

Is that still the case.


Good question for a technical forum

I couldn't tell from my read if the G reading was before or after it hit he ground. It does make a difference.

[Dutch74]

Where is the thread about the DC10 Hard landing?

[PJ2]

lomapaseo;
I couldn't tell from my read if the G reading was before or after it hit he ground. It does make a difference.
In flight data analysis, 'g' is usually sampled at pretty high rates. The 320 LFL (logical frame layout - the software "frame", something like a spreadsheet, into which data is recorded) records 'g' at 8x per second. The DFDR (crash recorder) on the 777 records 'g' at the same rate but our LFL for the 777 records it at 10x per second.

UDRI, the University of Dayton Research Institute (http://www.udri.udayton.edu/NR/exeres/E4C374CA-2BB3-4475-BBE7-52186E7C85FC.htm) with whom I and others have collectively worked in the past, does a very wide-ranging loads analysis program on different airframes including the 777. They wrote a paper (http://www.cgar.org/downloads/June2008/Thurs/Doug%20Marshall-Business%20Jet.pdf) a while back discussing the reliability of the 'g' parameter on the Boeing 777 because of the sensors' location in the cockpit area, (IRS's), instead of near/at the center of gravity of the airplane*. We concur with that finding, (no formal communications with UDRI - it's a known issue for the Boeing).

The reading and interpretation of flight data requires considerable "time in". What can appear a "holy cow", can in fact be a non-event. The reverse can also be true.

The Airbus 'g' parameter is 99% reliable in my experience although, like any data, it can in rare occasions exhibit a spike or two. The way to read the parameter, (which is obvious if one thinks about it), is to see what the readings before and after the highest reading are doing.

A "3.5g" reading does not occur in one-eighth of a second - it will have a "ramp up", "ramp down" of readings in the previous and post samples even if it occurs over a half-second, (four readings).

I have seen such readings and before apprising anyone we ensure that such readings are valid, using this and other techniques such as interpreting the IVSI parameter. Anything over 6fps (about 340fpm) usually results in a hard landing. We also look at the rate of change of the radio altimeter which is also sampled at between four and eight times per second, (the 777 has 3 radio altimeters and parameters).

Interestingly, the 777 AMM states very clearly that the pilot must first report a hard landing (or any other aircraft limitation exceedance) before maintenance action will take place. Once reported, the 777 has the usual limits which are then examined in the DFDR or QAR to determine what kind of hard landing check is required. In other words, if it is not reported by the pilot, it didn't happen. The Airbus philosophy is substantially different, where data is an integral part of the operation. I do not know why these differences obtain and do not wish to spark an AB "discussion". The one difficulty inherent in waiting until a pilot reports an airframe exceedance however is, such an exceedance is always available and known through the daily flight data analysis by the safety department personnel but, because of the way the 777 AMM is written, even though there may be significant exceedance indicated in the data, the operator is not required to do anything about it. For many including myself, there are inherent ethical, legal and technical issues outstanding in this approach now that data analysis is becoming not only routine but mandated under SMS.

Also, there is in place, a mistaken impression, principally from operations and maintenance personnel, probably not intentional of course, that views "QAR" data as somehow "inferior" to DFDR data and so can be safely dismissed when/if commercially inconvenient, as "advisory" only. QAR data is the same kind of peripheral as the DFDR and receives exactly the same digital data from the ARINC 429, 617 etc databusses that the DFDR does. If the data is bad for the QAR, then it is likely bad for the DFDR in which case there could be a pending legal issue. The prevalence of this view (that QAR data is "not valid"), is a regulatory matter and not merely an airline SMS issue. Anyway, enough thread drift - the 'g' readings on this 320 are almost certainly accurate, having seen them and analyzed them in other cases. If I recall, a "3.5" g reading exceeds 320 airframe certification limits by at least 1g if not 1.5g's.

-------------------------------------
* From the Abstract:
The B-777 airplane sensors, which measure vertical, lateral, and longitudinal acceleration, are located in the cockpit area. The estimates of the center of gravity (c.g.) accelerations are computed in the Air Data Inertial Reference Unit, which converts the measured crew station accelerations to accelerations at the c.g. For some dynamic and ground load conditions, inaccuracies could exist in these filtered c.g. time history measurements. Operators and inspectors who use the recorded B-777 acceleration values as maintenance action triggers or Flight Operational Quality Assurance events should recognize the possibility of recorded Digital Flight Data Recorder acceleration inaccuracies.

[lomapaseo]

PJ2

Agree with everything that you wrote :ok:

However my intrpretation of the quote below, that I replied in my post has to do with not the gross inflight acceleration changes (acting over a large body) but the unique decelleration loads near the G sensor once crushing has occured

[quote] 3.5 G landing, things may have changed, but we were taught in the Air Force, that G meters do not read correctly on the ground.

Is that still the case. /quote]

[PJ2]

lomapaseo;

I guess we'd need to know what kind of 'g' meter - mechanical or electronic, instantaneously reading or capturing data over time, or whether it just reads the highs (or lows).

In the 'g' data I've read, you can see the 'g' reading "climb" over a one second sample such that it forms a rough "bell curve" in a graph plot. Data that is suspect, instantly spikes to, say, 2.6, with no lead-in/lead-out readings.

So I can't really comment on military 'g' meters as I have no experience with them nor do I know how they work at landing but, notwithstanding the 777 issues with the 'g' reading, the Airbus readings are reliable in all phases of flight including on the ground, (where the vertical parameter is used to determine rough runways and the lateral parameter, high speed turns causing high lateral loads on the gear), and it is easy to spot spikey data and dismiss it as false. I can tell you that single-engine taxiing for example, will spike the 'g' parameter when the generator comes on/falls off line. It's just part of the interpretive work.

[ready eddy]

My bad, apologies to all!:ouch:

[vickers vanguard]

PJ2,

Are you saying that the G trace the FDR gets comes from the IRS in the 777? that's a weird setup, most of the aircrafts that I'm familiar with have a dedicated accelerometer for the FDR, and it's located more or less near the A/C CG....example: CRJ, Cl 605 etc.... By the way, the CL605 has dual IRS.
Before I forget, thanks for posting a link to that document, I started reading it and it's quite interesting.:ok::ok:

[Capt Claret]

I currently fly a Douglas/Boeing 717 that was repaired by the Boys from Boeing, after a 3.2 G heavy landing. They said it wasn't as damaged as some they'd seen.

[Canuckbirdstrike]

On the Airbus aircraft, the engine flight idle increases to "approach idle" setting, based on flap selection (i.e. Flap 1 on the A320 family) or the selection of landing gear down (widebodies). From the depths of my memory this is to comply with FAR 33.73 engine idle to 95% of take off thrust spool up time requirements.

Perhaps someone can take us through how this relates to the FAA 8900.1 order as cited by IGh?

If the approach idle setting on the Airbus aircraft meets FAR 33.73 requirements does that mean that it complies with FAA 8900.1 or do we need to have a higher minimu thrust setting? IF we do what is the minimu setting to be in compliance with FAA 8900.1?

[Canuckbirdstrike]

IGh, thanks for the detailed and informative reply. So far trolling through the Airbus FCOM's provides no clear answer on what that minimum thrust setting is to be in compliance with FAA 8900.1. I checked the manufacturer's document and a few airline specific ones.

[Cardinal]

I can attest that N311US, the NW Airbus that carries some distinction as it wears the Delta colors, has been sitting in DEN for the past month and hasn't moved one inch (or centimeter) from its hardstand (just north of and adjacent to Twy CN) during that time period.

[sb_sfo]

I recall in SFO on or about 1 Mar 2004 a DL 757 taxiing to the gate on Alpha was hit by a fuel tanker. #2 engine was totally trashed. No report ever on the NTSB site, someone must have some powerful mojo. I have pictures somewhere.

SB

[Chris Scott]

IGh,

No, the standard landing flap setting is known as "Flaps FULL".

In my day (1988-2001), Flaps 3 was recommended in turbulence, windsheer, and/or limiting crosswind. Many of us, however, found this unsatisfactory, mainly because of the FBW handling characteristics. (Flaps 3 is also a take-off setting, and this somehow affected them; there may have subsequently been a software fix.) The other slight disadvantage was the lower thrust setting, and the unfamiliar (higher) pitch-attitude (sorry, deck-angle!).

In the early days, before the double-acting L/G shock-strut was introduced, the only reliable way to get a 'greaser' involved an excessive amount of floating along a (long) runway. But I don't remember any of us doing a tail-strike... Needless to say, the latter would be more likely at Flaps 3.

Chris

[CONF iture]

Clearly this event is also no stranger to the "Evolution of Ground Spoiler Logic" as described in the Airbus Safety Magazine Edition February 2010. (Thanks fredgrav :ok:)

Also, and if still needed, this is another example how a dual input is the natural answer to a degraded situation. Or when the L/R side don't know what the opposite side is doing ... !?
Don't blame the crew here, but the system.

[Zippy Monster]

Don't blame the crew here, but the system.

If the captain is adding a nose-down input of his own while the first officer is PF, then he should push the take-over button to disconnect the F/O stick and take full control himself.

The sidestick/FBW system is not designed for 'corrections' to be made from the opposite sidestick, hence the 'dual input' warning being incorporated in the first place.

A small point, but worth mentioning when discussing how the crew reacted.

[Chris Scott]

Quote from IGh:"...this A320 lost 7-kts sometime in the flare. The PF controlled the PITCH-up response to the late sinker:
?? Was the A320's Thrust Mgt System suppose to respond with added POWER??"


Difficult to answer, as the published report leaves too many relevant questions unanswered, and we don't have the DFDR traces. These would be particularly helpful to establish the time span between the 2 reported touchdowns, and also to see if the main-wheels may have nearly left the ground a second time around the time the tail-strike occurred.

Quote from the report:
"At about 1202, as the flight was entering the DEN terminal area, the crew briefed an approach speed of 139 knots for a visual approach to runway 16L."

We do not know the SOPs in use. In A320 operations, however, it is not normal to brief a fixed approach speed, because in "managed speed" this will be reviewed constantly by the "GS-MINI" feature. What would have been briefed, however, is the VLS (VREF) for Flaps3. This figure is calculated by the FMGC, and displayed on the PERF page, but may be overridden there by the crew. Once the crew enters a surface-wind, the FMGC calculates and displays VAPP, which may be higher. This will be scrutinised for gross error. (CONF iture, please confirm?) With "managed" speed, GS-MINI never allows the airspeed target to fall below VAPP, but always increases it if necessary, to maintain a ground-speed not less than it has calculated for the threshold.

It is perfectly possible to fly approaches in "selected" speed, using the speed knob on the FCU; but inadvisable, because you lose the airspeed protection provided by GS-MINI.

The report (as published) does not cover any of these differences.

The stated LW was 140,000 lb (just under 64T). A VLS (VREF) for Flaps 3 of 139 sounds a bit on the low side to me, but my manuals are out of date. [Can anyone help?] We must assume that the crew had planned to land with Flaps 3, as the report does not state otherwise, but there is a small element of doubt in my mind.

The latest METAR available to the crew at the briefing stage appears to have given a wind of 240/4 kt, so it is likely that VAPP would have been the same as VLS.

The report continues:
"The First Officer (FO) was the pilot flying (PF) and reported the approach was stable at 1,000 feet above the runway threshold. At 1216:15 ATC cleared the flight to land and issued a wind advisory of 260 degrees at 5 knots. The flight crew extended the gear and selected flaps 3."

When the PF reported approach "stable", were gear and Flaps 3 already extended? The last sentence above seems to suggest otherwise, which seems odd. The final wind report (260/5 kt) from the Tower must have been due to change: about 30 mins later it was 330/13 kt, which may explain the tailwind they got on the approach from the north-west.

The displayed speed target should not have dropped below VAPP, whatever that was (139?). The A/THR should have tried to maintain that (or greater), until the PF selected idle thrust (during the bounce). The report says the DFDR indicated the tailwind was as high as 11 kt, late on the approach, but does not state a touchdown figure. If it had disappeared by the threshold, that would represent a headwind-shear...

The high VS of 800 ft/min at 50 ft probably reflects the high TAS (at over 5000ft amsl), plus the tailwind. If the flare was started at 45 ft, that should have been more than early enough.

So, to try and answer IGh's question, the facts are: the PF pulled hard to try and achieve a respectable touchdown; there was a loss of IAS; and the A/THR failed to arrest this. Why? The best I can come up with is: thrust would have been lower than normal, due to the high VS, and there [U]may have been a further, sudden tailwind-shear during the flare. In my opinion, the loss of speed was not due to anything peculiar to Airbuses, or the CFM-56. As for any comments on sidesticks, and/or the ground-spoiler logic, I'll try to leave those to CONF iture. He and I have been there before...

For what it's worth, I would have preferred to use Flaps Full. Would also like someone to check, please, if that reported VAPP of 139 kt was enough for Flaps 3.

Chris

[CONF iture]

IGh,
It has always been a sensitive subject for Airbus. On top of the Flight Crew Training Manual, they have published no less than 3 FCOM Bulletins explaining how to avoid tailstrikes, hard landings, and more generally how to properly handle the aircraft in final approach. They are all very informative readings, and all of them have a paragraph dealing with the crucial adherence to the proper speed, being Vapp (either automatically calculated, or manually overridden)
Mainly, they recommend using the A/THR, but in the same time they don’t try to hide that in certain circumstances, the result may not be satisfactory as :
A/THR response to airspeed variations is the result of a design compromise between performance and comfort, and is optimized when the AP is engaged. Therefore, in turbulent conditions and when flying manually, the pilot may sometimes find it to be too slow or lagging.
This is probably what happened in DEN. Aircraft was following the glide slope but with a tail wind component + only CONF 3, engines were probably at idle for the latest stage of the approach including the early part of the flare. A/THR responded but not as promptly as desirable :
At the time of initial touchdown, the thrust levers were still in CLB, and engine N1 increased from approximately 54% to 64% over 3 seconds.
Manual THR could have been, maybe, a better option here ...


Chris Scott,
I read the same figure of 139 knots for VLS CONF 3 and 64T, but to me, unless it is applicable for the A330 but not the 320 (?) Vapp should have had an extra 5 knots as the approach was conducted under A/THR …


Zippy Monster,
If the captain is adding a nose-down input of his own while the first officer is PF, then he should push the take-over button to disconnect the F/O stick and take full control himself.
The sidestick/FBW system is not designed for 'corrections' to be made from the opposite sidestick, hence the 'dual input' warning being incorporated in the first place.
Fully agree with your comment, but I would call it Theory, it looks good in the books but is not supported by the facts as seen in the incident reports.
In the heat of the moment, the take-over button is usually forgotten.

[Chris Scott]

Thanks, CONF iture,

If I read you correctly, the current book VLS for A320 Flaps3 at 64T is 139kts? (So, as I thought, my book is indeed out of date.)

Because of the light reported wind, as presumably entered by crew into FMS PERF page, it looks like VAPP would have been the same as VLS. (See my previous post.) As you know, I haven't flown A320 since end of 2001, but am not aware of any requirement to add 5kts for use of A/THR on the A320 family. (We used to add 5kts for autoland.) Can anyone comment?

Agree with you that manual thrust is nearly always a better option, when you are flying without AP. But few others would share that opinion :{.
Also agree that, in practice, the sidestick takeover button is rarely used.

Igh,

I think CONF iture has a strong point. This apparent lack of response may be more of an A/THR problem than a CFM-56 engine/FADEC problem. I often felt, however, that N1 was uncomfortably low on Flaps3 approaches. The reported N1 of 54% is the kind of low figure that – if memory serves – used to make me uncomfortable.

Chris

[rudderrudderrat]

Hi Chris Scott,

We use FMGC derived VAPP which adds a minimum of 5 kts to VLS.

It's only when we've had some sort of failure which increases the landing distance - and the runway is so short, that we use VAPP = VLS.

A320 V APP (http://www.merrowresidents.org.uk/PDF/A320%20V%20APP)

[FlightDetent]

@Chris:
http://img101.imageshack.us/img101/9486/qrh400a.th.gif (http://img101.imageshack.us/i/qrh400a.gif/)

[Chris Scott]

Hi rudderrudderrat and FlightDetent,

Thanks for your quick responses and links – just the job (my manuals really are showing their age...). References to the Airbus term "CONFIG", instead of "FLAPS" are in line with my own preference, although my airline preferred the latter. The NTSB uses "flaps", so I'll stick with that.

Interesting that – as CONF iture said – the mandatory 5 kts increment now applies to both A/THR and Autoland landings, instead of being only for Autoland, which was the rule in my day. Maybe Airbus has learned from our (old farts') experiences of A/THR response in gusty conditions!

Assuming that the tables applied to the FAA-registered accident aircraft, a VAPP of 139 for A/THR implies a VLS of 134, which would be correct for Flaps FULL, not Flaps 3, at 140,000 lb (just under 64T).

Nowhere can I find confirmation in the NTSB report of either:
(1) the briefed landing configuration; or
(2) the actual landing configuration.
It's tempting to assume that they both briefed and landed Flaps 3, but the ambiguity in this (rather brief) report remains.

If they briefed for landing with Flaps 3 – and the report merely says, "the crew briefed for an approach speed of 139 knots for a visual approach..." – they appear to have briefed 5 kts slower than standard.

The report does not mention the actual IAS on the approach, before the flare. If it was 139 kts, and assuming they landed with Flaps 3, that would appear to be 5 kts slower than standard. This would obviously be a disadvantage in any tailwind-shear.

Chris

[CONF iture]

Chris Scott,
You are correct, it is not clear cut, there are some conflicting information : Flaps 3 ? Flaps full ?

IGh,
Would you have a link for the MD80 report at Denver ?
I'm always amused when a pilot reports "I increased thrust" during an un-spooled approach, and then the FDR shows NO CHANGE in thrust.
Is it possible there is something to see with DEN higher altitude which is above 5000 feet ?
It is especially noticeable when taxing out on single engine for these higher altitude airports where the thrust lever displacement in order to initiate the initial forward movement has to be more significant than in Minneapolis for example. The first one inch of thrust lever displacement seems to produce nothing.

On the A/THR side, it is common knowledge that Airbus, for the last 20 years, has been widely encouraging the maximum use of automatism and as a consequence I have noticed some discomfort as well as confusion for a pilot to disconnect the A/THR in the last 200 feet RA if needed to correct a basic situation. It is almost as if it was more simple to just go-around. (which is not bad either)
The following realignment was inevitable :
Pilot handling skills under threat, says Airbus (http://www.pprune.org/rumours-news/388573-pilot-handling-skills-under-threat-says-airbus.html)

[tildeleb]

I am an engineer and not a pilot. Some interesting similarities to this incident and the LH44 incident. In both cases you realize how vulnerable planes are to changing wind conditions at less than 50' AGL. Also (in my opinion) in the case of LH44 the FCS failed them as soon as one wheel hit the ground because that sequenced the FCS logic from Flight Mode to Ground Mode, which limited pilot control of the plane.

1. Does anyone think that FCS transition from Flight Mode to Ground Mode upon wheel touchdown could have been a factor here?

2. Should they have moved the throttles from CLB before they touched down? The FMS told them to. If they had moved the throttles to IDLE would everything have been OK? How does that jive with #4 below?

3. Like LH44 both pilots were trying to fly the plane which just seems wrong to me, but as a previous poster mentioned probably impossible to overcome from a psychological standpoint when something is going wrong.

4. Can I ask a naive question? How does one keep the engines spooled up on approach without getting lots of thrust and having to deal with that in a situation were you don't want that trust unless you need it. I.E. how do you avoid being behind what Naval Fighter pilots call the power curve, nice chart from user IGh below.

[Chris Scott]

Hi tildeleb,

I've the opposite problem to yours: am not an engineer. As a long-retired A320 driver, I'm not going to comment on any comparisons with LH44 at the moment, as my own manuals for FBW F/CTL logics are obsolete. We had (and still have) one or two threads running on it. Recommend this (http://www.pprune.org/tech-log/316096-lh-a320-rough-landing-hamburg.html?highlight=lh44) one in particular if you have the time and patience...

Just want to look at your Q4 now.

Is there an engineering definition for "spooled-up"? We certainly used the term on the JT3D, "standing-up" the throttle and waiting for the engine to "stabilize" before opening the thrust lever at the beginning of the take-off run. On a FADEC-controlled CFM-56 this has not normally been necessary, and the smooth modulation of N1 acceleration tends to mask hesitation, that might otherwise be apparent, at any particular RPM.

The graph of typical thrust-versus-time during acceleration, provided by IGh, is very interesting. But it presents a problem for us pilots: we do not have a thrust gauge, as such. Being stuck with N1 (or EPR) as our prime indicator of thrust makes comparison with the graph difficult, if not impossible. For example: would half the N1 RPM deliver a quarter of the thrust? Experience suggests less, but it's not something that we are made aware of.

How does one avoid low thrust, when stabilised at VAPP in the landing configuration? On most jet airliners, all we can do is to select the maximum slats/flaps, avoid getting above the "glide-slope" (a misleading term), and avoid strong tailwinds. Use of speedbrakes (airbrakes) is effectively prohibited on final approach on most of the A320 family (A318s with "steep-approach" capability being an exception). Few other types allow it, although the F28 /F100 and BAe146/AvroRJ routinely use their tail-mounted airbrakes, I believe.

Chris

[tildeleb]

Hi Chris Scott,

Thanks for your answer to #4, about what I expected, which is flaps and slats.

I agree N1 is a poor substitute for thrust. These days I am positive they have computer models of the engine that are very accurate. It would certainly be possible to make a gauge that read real thrust where that gauge calculated the real thrust from other engine sensors.

One of the sad things about the glass cockpits of today is that they essentially have digital versions of the same analog gauges that have always existed. A real thrust gauge is a perfect example of something that would have been hard or impossible to do in analog or early digital (not enough compute power) but would be very easy to do today.

What other gauges would pilots like to have that don't exist? Hmm I think I'll start a thread on that one. Watch for it.

As far as LH44 goes it is very interesting to read the final report. Let me know if you need a pointer to it. I looked at LH44 extensively and wrote my opinions in a post on the LH44 thread. However what I found interesting is that some of the posters really think is was just yaw induced roll and I didn't see it that way at all.

[CONF iture]

Should they have moved the throttles from CLB before they touched down? The FMS told them to. If they had moved the throttles to IDLE would everything have been OK?
Of course the RETARD auto call-out is a reminder rather than an order, but if thrust levers were retarded a fraction before initial touchdown, ground spoilers deploy in time and rebound is minimized.
Actually, by the logic of the automatism, they used the worst possible timing for retarding the thrust levers as this action was the trigger for the ground spoilers to deploy but the airplane was already back in the air for this consequent bounce.

Radio altimeter values increased, indicating the aircraft then bounced. The FO held 16 degrees aft stick input (approximately full aft travel), and moved the thrust levers to idle during the bounce. Ground spoilers deployed (thrust lever position and wheel spin up logic was satisfied)
Here is another point I want to make ... one more time :
Pilot Flying is full back stick but Pilot Monitoring has no information on this unusual fact. Having coupled side sticks or conventional control columns, the PM would have known how hopeless was the situation and a perfect warning signal for him to take over for nothing less than a go-around which, by the way, is the manufacturer recommended procedure in case of high bounce.

This is my reminder to all FBW Airbus pilots, myself included :
Be aware how your independent sidesticks may deprive you from a valuable source of information

[guiones]

CONF iture touched the main point most are missing, it is not Auto Thrust or the tailwind that caused this incident/accident; it is the improper reduction of the Thrust Levers to IDLE, the Auto Trust worked as advertised; it increase power trying to maintain VAPP and that plus the fact that the Thrust Levers were still in the CLIMB Detent caused the big bounce. Proper and timely retarding the Levers to IDLE would have minimized the bounce. Of course the handling of the Side-Stick by the PF is also at fault; the landing on FBW is not a flare, but a change of attitude and let the aircraft settle. The aircraft is designed for positive landings, not pilot pride greesers. There is also a very good document by Airbus on Bounce Recovery, should be standard reading for all FBW Pilots.

As mentioned before, RETARD is a remainder that the Thrust Levers should have been retarded by then, NOT an order for the Pilot to wait for.

G