A320 Selected speed below 700 ft
 

Hi I am new here, so not sure its in the correct place.

A320 Situation: on short final below 700 ft late landing clearance received crosswind 10 kts gusting 20 kts.
It is advisable to go selected speed and add half of the difference (5kts)?
thanks for your answers.

No. The 320 GS function works admirably and below 700 feet you should be flying the aircraft the way you did the performance calculations for, not arbitrarily inventing procedures.

Nope, selected speed is a sure way to end up in the office! Trust GS MINI to do the work for you, if you can’t land because of GS MINI then don’t land.

+1

Why would you, (9airbus), want to do that ? You have flown all the way down the approach with groundspeed mini and the auto-thrust looking after you and maintaining your aircraft energy - why take that away in the last 30 seconds very close to the ground, and risk losing energy and destabilising ??

Use groundspeed mini and the auto-thrust - they have been designed and developed to deal with this sort of thing, and they do so very well.

Don't be alarmed if the engines spool up with a headwind gust, they won't increase your groundspeed, and won't destabilise your landing.

my thought:
As GS mini only takes the headwind component into account it would not add any speed on a high crosswind gust below 700 ft.

If you expect a loss of energy near the ground (crosswind changes to tailwind) then this should be accounted for in the planning with an increment to Vapp, not going to selected speed at short notice.

GS mini takes tailwind gusts into account as well as headwind gusts, (within certain limits).

GS Mini reacts to the instantaneous head or tailwind gusts, and is automatically smoothly reduced so as not to ​​​​​​command high speed changes in the flare.

Pulling selected speed stops GS Mini from working, and that could reduce the aircraft energy below a safe level. As Fursty Ferret says; GS Mini should be programmed with the Tower Wind before commencing the approach; not overridden on short finals.

Old conventional systems have to fly fixed IAS, because any change in IAS affects the pitch trim, so this would cause the aircraft to deviate. Airbus FBW auto-trims, (and also designs-out the pitch/power couple), so the designers could look again at the situation and did not need to stay with fixed IAS.

GS Mini takes the reported Tower Wind into account and computes a minimum groundspeed - and therefore a minimum energy - instead of a fixed IAS. In practice therefore, it reacts the opposite way round from the old conventional constant IAS systems - GS Mini will call for increased thrust during a headwind gust, and vice versa, (within certain limits). It does this to preserve energy, so if you cancel or override an IAS or thrust increase commanded by GS Mini, you are reducing the aircraft energy, which could leave you in a bad place.

Do you have an FCOM reference? Unless the tower wind has a tailwind component you won't get an increment on GS mini.

​​​​​​​Having experienced a shift to a tailwind below 100ft when the tower reported calm winds, I can tell you from first hand and a sore back that the GS mini does bugger all in this situation.

My old FCOMs are packed away and my electronic FCOM is not playing, but I will look when I have worked down my "to do list" of house maintenance projects a little further !

I sometimes slightly delayed retarding the thrust levers if my RoD just going into the flare seemed higher than normal.

Hi,

GS mini function is not related to increasing/decreasing tailwinds, it is an energy management tool for increasing/decreasing headwind components.

https://cimg4.ibsrv.net/gimg/pprune....741944d5b.jpeg

The k factor reduction does not apply to the A320ceo.

I guess what you mean is that you planned the approach without the gust, and didn't add anything to Vapp, and now you have a gusty crosswind, but it is too late to change Vapp.
My company allows for us to land with selected speed, but it is definitely not recommended. Use cases are being close to a 737, with a lot of HW on the approach, but lower winds on the field. GS-mini eats up the separation.
Gusty crosswind does not have the same impact on energy as gusty headwind. You will be correcting LOC more than GS, but that does not affect power, so I would not go selected because of crosswind gusts. And I will disagree with most here, I do think it is okay to use selected if the HW gusts increase on short final. GS-MINI is great, but it doesn't have an additive for gusts. AB does recommend an additive for gusts, so....

I think his q was about crosswind, not HW.

You might disagree with most if You make up your own procedures.

https://cimg9.ibsrv.net/gimg/pprune....f781654c8.jpeg

If the wind is causing the airspeed to jump around too much, I’d just disconnect the AT and leave the speed managed.

You’ll be able to see what GS mini is doing, while flying a speed that you feel is more sensible. Win-win

By reacting to gusts like that, the auto-thrust is working as designed and keeping you safe. Why prevent it ?

From the Airbus A320 Family Instructor Support manual: UDY0102 Jan 2001:
And, Hans; the whole point of GS Mini is to react to gusts and adjust the thrust to stay above a minimum energy, so it most certainly DOES adjust for gusts !! - that is its whole purpose.

Why disable this vital system just because you don't like the engines spooling up like that ? We cannot know the instantaneous wind*, so how do we know what is a safe speed/ energy/ thrust setting ?

* the three ADIRS do though
.

Correct by all means. It is important to note, to avoid misunderstandings, that GS mini is primarily designed to deal with headwinds in order to maintain, as the name suggests, a minimum Ground Speed during the final approach.
The great advantage is to have the IAS increasing with headwind increase, hence if the headwind components drops or shifts to a tailwind the aircraft will not be in a low energy state with IAS dropping and low thrust.
In case of an approach with wind calm or 0/0, an increase in tailwind will be dealt in the same way on an Airbus FBW with managed speed as any other type, i.e. there will be the need to increase thrust to maintain the computed Vapp (Vls+5).

In twelve years of A320 I haven't landed with selected speed more than a very few times. All of those times the wind suddenly became much more gusty than forecast in the last 1000' (LAS in the summer: VAR10 G30 just as you get close, before that reported as calm....) . And it is not my made up procedure, we are specifically allowed to use selected for A) traffic ahead does not have GS mini, so have to reduce speed below GS mini (never below Vfas of course) and B) Gusty conditions on final when too late to add gust factor in the MCDU. I do know how GS mini works, and I have that same instructor manual. I am not afraid of the increase in thrust during a HW gust, because I know what it is doing, but I have seen without the gust addition the speed going below Vls during TW gusts. So for those cases I would rather select a higher speed and lose GS mini. The higher speed gives more buffer for TW gusts, and with HW gusts the thrust reduction because of no GSmini doesn't adversely affect the energy state as much because the higher buffer from Vls.
Also, the original question was specifically for Xwind gusts, and GS mini is just about a HW component addition to Vfas, no addition for Xwind.
And I am definitely not suggesting using selected just because your magenta bug seems too high/going up and you don't understand GSmini.....

I think I found the right thread to hijack (sorry)...

If Vapp = 130 Kts and GS Mini has you indicating 141 Kts at below 500ft, is that classed as a "stabilised approach"? If so, why.

Thanks

Your objective is to be within Target speed +10/-5 or whatever your operator specifies.
Target speed is Vapp + GS mini compensation. Hence your reference is the “magenta” bug (Target speed) on the speed indicator.As long as your indicated airspeed is within the specified margins from the Target Speed your approach is stabilized.
Momentary deviations due to environmental conditions are obviously accepted.

In gusty headwind conditions VTGT will vary all the time, so as long as you are close enough to that speed you are stabilized.

@SA, no problem; It is still stabilised because even though the engines might spool up; your groundspeed won't significantly change, and when meeting the runway it is actually the groundspeed that is important - as long as the wings are still safely flying, which they will be, because they will be between VLS and VFE.

So, although it might sound and seem as if the aircraft is suddenly going to accelerate forwards, it actually isn't; it will actually "stay where it was" on the path and ground speed that it was on before the gust.

The increase in IAS will not destabilise the aircraft path, (as it would in conventional constant-IAS types), because the FBW automatically corrects the trim for the IAS change AND nulls-out the pitch-power couple.

The engines will remain spooled-up, which is also a stability requirement, as you know, and the effect of GS Mini is reduced approaching the flare anyway.

Are you a member of the team who thinks a dry 4000m could not suffice for a standard 320 with no failure ?
And who would check that at each and every flight, just to make sure ?

In answer to the latter, I am - it takes seconds and gives me an idea of what exit I can expect if it’s somewhere I am less familiar with. Beyond that it is my company’s SOPs (that I am paid to follow) to do one, it is also a legal requirement per CAT.OP.MPA.303 to do an in flight check of landing distance at time of arrival using AFM data (if there is sufficient time in a non critical phase of flight).

Why wilfully violate an SOP and legal requirement because “It’ll be fine” when a 30 second perf calculation covers me? Not doing one is laziness for the sake of it and, if something subsequently went wrong, is utterly indefensible.

When I flew Boeings, we were told that 70% of overruns are not on “short” runways but are on runways of over 2,400 metres but people get complacent. Make of that what you will.

Edited to add: day to day I try to operate such that nothing I do would make me (or the training department!) shake my head if I read it “in the subsequent report…”. This was drummed into me many years ago, and thus far it has worked just fine, thanks.

Why wouldn’t you do a Perf Calc? Surely you can’t be under that much time pressure.

Because it has literally no use.
Let's try to get some meaning to it.
The simple calculation mass*30+300m with A/BRK LOW and mass*20+300m with A/BRK MED will give you a result that is correct 100% of the time where you don't have outstanding tailwind, and a correct braking action (5 or 6, when the LOW/MED deceleration target can be met), to a precision within 100 meters.

So it's not that you're not doing the perf calculation. It is that it can be done with a sufficient level of precision in your head.

The on board performance tool asks you for temperature, QNH.. What kind of difference will one hPa of QNH create ? Around one meter per hPa. One degree ? Three meters. One knot headwind ? 8 meters (tailwind contrarily is significant). Flaps 3 ? Add 100m.
(these are all ballpark figures based on A320 at medium mass with a dry runway)
Do you really think that a figure with an accuracy to one meter has any meaning ? You are splitting hair.

Do you know immediately by heart the touchdown distance that is assumed by the computation ? Because if you care about 10 meters on the result, you should. Also, you should be able to control your touchdown point to around a tenth of a second.
I don't think I'm able to touch down with a precision anywhere like this.

So yes, I prefer to have a real analysis of the situation, intellectualize it, rather than stuff numbers into a computer and mindlessly read the result. I will happily launch a computation in case of any doubt. 99% of the time, the rule of thumb above will have more precision than the touchdown point.
The touchdown zone is 600 meters long !!

When we landed at particularly long runways, I always computed the perfs with the worst possible failure. All brakes fail. The captain would wonder how I ended up with such a result. Pointing that the runway is long enough without the use of brakes proves that the computation was unnecessary...
Also, this computation shows that the perf tool is pessimistic. For the case of a long runway with no braking, the actual performance with reverse idle is close to the computed performance with reverse max.

My comment was specifically designed as an answer to yours. You said that 700 feet on final was not the time to wonder about performance calculations.
You usually compute the perfs in cruise, at least 30-40 minutes before landing. The ATIS that you use is going to be older than this.
Let's say you computed the perfs with the latest ATIS and put the wind into it.
You have 3 knots less of headwind, and you learn that on short final when cleared to land... what are you going to do ? Go around ?
You receive a new ATIS with two more degrees or 1 point QNH less. What are you gonna do ? Ask for a hold to re-compute ?

So, to sum up, a pilot should have a sufficient mastery of the perfs. Knowing how to do a calculation is not enough.
You also need to know the hypotheses that are used, you should have an idea of the result before calculating it, in order to be able to detect a gross mistake. You also need to know approximately the influence of each parameter on the result.
I would be surprised if the guys who took off with a 100 ton error and struck the tail (happened to several airlines) had this kind of mindset.
Ballpark thinking will allow to detect gross mistakes like so.

It took you 50 times as long to write that reply than it takes to do a performance calc. That’s all nice what you wrote and I agree, I have gross error figures in my mind for many different conditions and weights so that I can pick up something that is ‘off’. Problem is though that Airbus says a performance calculation should be completed for every landing, so the real question is, if the book says to do it, so why not just do it? And if you happily ignore that Procedure, what procedures in addition to this are you happy to ignore? As a sim instructor I also know what figures I can chuck into the box to get us going for a multitude of different conditions, would you be also happy for me to use my own figures for takeoff as what is the point of the perf calc if I know what will work.

Landing computation in flight is not required by Airbus. Unless major weather changes since the dispatch calculation or failures affecting the performance. Our Outfit still requires to do it tho..

No one deliberately runs off the end of a runway but performance calcs will very quickly tell you if the potential exists. I had a Training Captain operating as an F/O who stated in his brief that there would be sufficient runway. When i did the numbers from the QRH it said there wasn't when the buffer was factored in. We went A/B medium for this reason:

On the issue of GS Mini either use manual A/T if you are not comfortable with conditions or put a few knots in the FMS, either way let managed speed look after you but you keep control of the situation.

I don’t know under which regulations You do fly, but this is what EASA has to say about it (as already anticipated by the excellent post of Speed_Trim_Fail )

AMC1 CAT.OP.MPA.303 In-flight check of the landing distance at time of arrival — aeroplanes

a) The required landing distance for dry runways, determined in accordance with CAT.POL.A.230(a), contains adequate margin to fulfil the intent of the assessment of the landing distance at time of arrival (LDTA) on a dry runway, as it includes allowance for the additional parameters considered in that calculation.

(b) The required landing distance for wet runways also contains adequate margin to fulfil the intent of the assessment of the LDTA on such runways with specific friction-improving characteristics, as it includes allowance for the additional parameters considered in that calculation.

(c) When at the time of arrival the runway is dry or is a wet runway with specific friction-improving characteristics and the overall conditions, including weather at the aerodrome and runway condition, have been confirmed as not changed significantly compared to those assumed at the time of dispatch, the assessment of the LDTA may be carried out by confirming that the assumptions made at the time of dispatch are still valid.

So, assuming you have done your landing dispatch calculations beforehand and that the above conditions are met, you are “good”. If you haven’t then you are not, even on a 4000m dry runway.
With ref. To the rules of thumb calculations suggested at the beginning of your post, I must say that in 31 years of flying Airbus FBW I have never came across it… and back in the day there was no Flysmart, or Octopus.
Calculating your IFLD gives you a good idea of where you will be vacating and your stop margin, increasing situational awareness, especially in case of floating and landing at the very last bit of the touchdown zone, which is still legal, but eats up a lot of runway.
Flysmart contains protections with respect to head/tailwind considerations and varying conditions. It is all described in the related manual.
Tip: if You are a FO, don’t cut corners, that is likely the attitude that could put you in troubles for a future upgrade.
You need to think out of the box when there is not an apparent solution, not when there is one…

Most guys at my airline in gusty conditions never used selected speed. They did however disconnect the auto thrust. Makes for a much smoother approach.

Spot on. Making a calculation with the performance tool without having a clue if those numbers are ballpark correct is the same as making none at all.

My company has taken the step of doing the performance calculations for us. It’s a rare day when we actually need to do landing distance calculations. We know the airplane will stop on a 3000m runway on a “normal” day.

Are you being sarcastic or are You serious?

By and large the groundspeed mini works well on the 319 or 320. However 321 is a different animal.
Consider shortish runway, wet, gusty xwind , dark and minimums, a/t and g/s mini best not used. It will bite, with huge power changes close to the ground
leading to float due also to the more pronounced ground effect peculiar to the 321

I don't think there was ever one crew on a commercial airliner who overran the runway because they had not computed the perfs.

I am going to check as many overruns reports as I can, but from my memory, the vast majority happened not because of an insufficient TODA in itself, but because the approach or the landing or the braking, or several combined, were not conducted in a satisfactory manner.

Let's start :

Southwest 1248 : lack of familiarity with the autobrake system leading to a very delayed use of the reversers

Hawaian airlines 481 at Tahiti : landing inside a thunderstorm with a delay in the use of spoilers

AF 072 (nicknamed "the GITANIC") : landing with power on one engine out of 4

TAM 3054 : landing with full power on one engine out of 2

AF 358 at Toronto : the runway was sufficient, but the problem boiled down to landing and braking technique.

American 1420 at Little rock : landing in a thunderstorm

B747 Qantas 1 : go around initiated but aborted, then reverse thrust not used, one engine left at TOGA

This report also says that the majority of overruns happen when the runway is wet or worse, and when the airplane energy is too high during approach.

Air india 1344 : long landing, flooded runway

Pegasus 2193 : inadequate braking technique, excessive energy on final

Saha Airlines : they got confused and landed on the wrong runway, which was much shorter. No doubt the perfs calculations were perfect for the intended runway.

Skylease cargo 4854 : inadequate braking technique



I am not going to look at the entire list of runway excursions that are listed on wikipedia, I did not find one occurence where the crew elected to land on a runway that was too short. Not one. If you find at least one, please point it out. All occurences were due to an improper flying or braking technique.



Even if a crew overran a runway because of an insufficient distance (with a correct landing and braking technique), without having calculated the perfs, the fault would still reside in the failure to identify the factors leading a runway that is usually enough to be insufficient that day.

Because if a crew does not recognize the factors leading to an increased landing distance (slipperyness, aircraft failures, tailwind, ..) there is a chance they would have ignored that factor too during the perf calculation.



In my opinion, having a rule of thumb is necessary to fully understand what we're doing, as well as understanding all the assumptions. The manufacturer should provide it (still an opinion), but they don't, maybe because they think it would encourage "complacency" (even though it would not). I prefer to fly with a captain who won't compute anything the 999 times that he's sure it's not necessary, and does it the 1 time that it is required, rather than a captain who will compute everything the 999 times, and not do it the 1 time that he needed to, or miss that time an important element that lead to a stopping distance issue. Or that does everything correctly until the moment he lines up on the wrong, shorter runway.



Saying that if I "ignore" that procedure (it's a tough call to say I'm ignoring it when I'm writing literaly pages about it), makes you wonder about what other procedures I would ignore, is a slippery slope argument. You can conclude by yourself what type of rules I "ignore" : the ones that don't have a rational basis. For example at my airline we have a double sided bus station. One side goes from the security control to the car park, and the other side goes from the security control to the planes. On one side, the high vis jacket is required, as if we were already on the planes parking. On the other side, nothing is required. But both sides strictly resemble a normal street with buses, sidewalks.. This rule is enforced by fines up to 1000 bucks, which is why I don't "ignore" it, but I can argue that this is stupid.



There are very few rules that are stupid (lack rational basis) in the airlines. (Most of them are found at security checks on the ground, imo)

And on this topic, the regulation seems to confirm my arguing because the perfs calculation isn't mandatory in flight, as cited above. As long as the crew has evaluated the situation, the AMC (which not the same level of regulation as a law) allows not to redo it.



To me, this debate sounds like an issue of skills vs legal covering. But you don't need to be covered legally if you know what you're talking about.

In my experience of 2000 hours until now, I have observed a pattern that the most confident captains, who put the airplane in an undesired state the least often, tend to apply the rules with more analysis and common sense, whereas the least confident ones, who know they are more prone of causing an undesired state, will make more cautious decisions in order to be "covered". For example I remember a captain who stopped the airplane mid-taxi because he was informed by ATC that some taxiway lights were missing. At an airfield that we practised several times per week, and during a night with very good visibility and fully functionning aircraft lights. We ended up finding that... there is no clear rule in our ops manual as to which taxiway lights are required to taxi at night !



So yes, long story short, if you feel the need to add 5 knots on final, do it. (But if you're landing a heavy 319/320 at the wet Firenze (LIRQ) runway with tailwind, don't do it)



The takeoff perf matter is very different in my opinion. You can takeoff with a wide variety of takeoff mass, especially on a long haul plane. And the goal is to optimize the flex temperature, so for that obviously you need the computer.

But then again, let's take a step back. Have you noticed that the flysmart app will give you higher Vr for the same mass if you choose a longer runway ? That means that you could rotate lift off before the computed Vr and the airplane would fly normally, only in a less optimized manner. As long as you're above the real minimum Vr. I found cases with up to 30 knots difference between the minimum Vr and computed Vr, for the same conditions except departure intersection.

The incidents and accidents that happened during the takeoff phase due to incorrect calculations only concerned the most severe mistakes. Flap setting and gross errors regarding the mass. Overlooking icing. Wrong aircraft or engine type... Much of the rest is negligible.. We still input all the parameters to save a little bit of money.

On A320 I would say even in abnormal conditions. Even in clean config( no flaps & slats), a VAPP of 185kt at max landing weight and 10kt tail wind you would stop the aircraft well before the end of the runway assuming using proper technique. Apart from serious failures like G+Y a 3000 meters dry or wet runway should never be a problem. Like CVividasku says, overrun happens due to pilot errors.

Yes. It seems like a clear plain case of opening the umbrella.
Umbrellas don't fly planes.

I am going on a well deserved leave, so I won’t spend time arguing on the several highly debatable things you’ve written above. I just quoted a bit of a scary sentence that clearly sums up the way you think from the highness of your 2000 hours. Just ask yourself what if the rules that do not make sense to you today, start making sense tomorrow. Luckily you will have someone sitting on your left hand side reminding you that some stuff still needs to be done even without any apparent meaning.
With respects to citing incidents and accidents: yes people ended up in the grass because of improper landing techniques or other operational decision errors, but this does not mean that you need to induce even more threats to the already existing ones by “ignoring” procedures that do not make sense to you. You need to ensure that you have done everything in your hands to prevent an event from happening, and if stuff still happens, well it’s in the risk matrix of aviation. You will be judged mainly by what you’ve done to prevent an event should things turn sour. Watch out, legality is very important. If something goes really wrong your last concern will be tea and biscuits with the chief pilot because you might need to spend time talking to a public prosecutor whom in turn will ensure that the boxes about what you were expected to do have been ticked.
Bottom line is: watch out, as the sentence I have quoted above could be the barrier between you and a LHS position one day.

My outfit (major EASA operator) requests a performance assessment of the landing distance at time of arrival, however clearly states in the OM that "assessment" does not necessarily mean a performance calculation/computation if the landing performance is not to be considered limiting and the calculation may be replaced by flight crew judgement/knowledge of the landing performance.

Personally I like the pragmatic and common sense approach and for me it works well during line ops. Most of the colleagues won't do a computation on non-restricting 3000-4000m runways dry / wet. However almost all go for it on shortish runways (even at homebase) and on contaminated.

Same EASA ruleset - different interpretation and application by the operator and competent authority than above. What is called "cutting the corners" and not following the rules in the posts above is considered normal here legally approved. No offense, but I wanted to show that not every operator treats the issue in the same way.

Excuse me, but even the thing that you are arguing about, is not strictly required by law.
So even on the purely legal field, you're not right about what you're saying.

Not computing the perfs inflight has never caused a single accident/incident (if it has, please point it out).
Computing the perfs inflight is not even a legal requirement.

That makes two very clear points against your opinion.
Then there is the post just above who does exactly what I advocate : assessment does not necessarily need a calculation.
Which is a third very strong point.

However what did cause accidents related to perfs calculations is two things :
- Inability to understand that calculations have assumptions that must be met, or inability to meet them
- Inability to detect gross errors about takeoff calculations

To finish with, don't bother too much about my career. I know what opinions not to say in a training context. And know when and how to debate them to promote my point of view.
I'm just out of a type rating : my trainers valued my way of thinking and promoted it with a better mark in the "knowledge" competency.

Under EASA regulations You are at least required to compute Dispatch Landing requirements as I quoted a few posts above directly from the regulations. If your operator specifies otherwise then happy days. I wonder how you ensure that you comply with GA gradients without running in-flight landing performances (yes we could lose an engine during a normal Go Around -birds?).
I wonder how you can land with idle reverse (noise sensitive place, hello?) on a wet runway without running the in-flight landing perf. By using RCC 2 and select the appropriate auto brake that complies.
I wonder how you can demonstrate that you can use auto brake low on a short runway with RCC 6 or 5 because the LD is below the FLD and you have no brake fans (medium will kill your short turn around with those lovely summer temps…)
Anyway enjoy it as you like it, I am no one to tell you to do otherwise. 😄