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Old 11th Aug 2017, 21:47   #21 (permalink)
 
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Are we talking IAE or CFM engines? The difference couldn’t be bigger.
The IAE are small, but have high residual/idle thrust.
CFM engines are larger, but have much less idle power.
You can retard the thrust levers on an IAE A320 at 70 ft no problem, and airspeed will hardly decay. In a tailwind condition there is a pronounced tendency to float.
With CFM engines it is not advisable to retard them higher than say 20 ft, because as soon as they spool down the bus is going to sink like the titanic.
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Old 12th Aug 2017, 00:35   #22 (permalink)

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The math does not need to be complex to understand of the differences.

--- start part one ---
An average A320 with 140 PAX will have approach speed of 130 knots. If the aim is to bring the aircraft from 50 ft ILS THR crossing height to an identical touchdown point (say) about 450 m down the pavement...

... given just 3 knots of TWC vs. HWC ...

the kinetic energy to be managed is 513 MJ compared to 468 MJ. Now, the aircraft aerodynamically still flies Vapp = 130 kt at the beginning of the manoeuvre, so the "steering powers" of the pilot are essentially the same, however we drive a very different beast.

It seems rather unavoidable that a different set of inputs is required to obtain the same desired trajectory.
---- end part one ----

--- start part two ---
The manufacturer explains that typical loss of IAS during the flare is 7 kts. Somewhere between 30 and 10 feet, the wind does slow down by approximately 3 knots (my empirical observation). 10 feet being the reported anemometer value and close to bottom-of-flare, i.e. 3 kts on ground, 6 kts at the top of the flare.

Due to aircraft inertia and the short time-frame when this happens, relative airflow changes and that translates to change in IAS. Thus for a headwind situation: the partial loss of the component when entering the boundary layer over the ground "takes away" 3 knots and the pilot flies the flare whilst slowing down by 4 knots by his own making.

In a tailwind situation the loss of tailwind relative to the A/C creates an increase of IAS by those 3 knots. Here the pilot needs to fly the flare so to reduce IAS by 10 knots.
--- end part two ---

If we would discuss a situation of +/- 5 kt on the ground, I dare to draw the following illustration:

--- figure 1 (imagination required) ---
IDENTICAL for both TWC and HWC:
An aircraft of 58 tonnes and IAS 130 kt follows an asymptotic trajectory from ILS THR crossing height of 50 ft to a touchdown point 450 m down the runway.

DIFFERENT:
HWC: The kinetic energy is 432 MJ, and we need to slow down by 4 knots.
TWC: The kinetic energy is 552 MJ, and we need to slow down by 10 knots.

---- end ---

DISCLAIMER: None of the above should imply me advocating techniques outside the FCOM / FCTM guidance. On the contrary, myself I am a hard core believer in chapter, verse, word and letter of those books (with logical exceptions ). My claim is that a different colour of magic is required to achieve a similar result, just like two instruments playing the same acoustic tone.

WARNING: The above applies, in my opinion, even before we factor in the FLARE MODE and dynamics of handling the thrust levers on Airbus FBW designs. And that’s another potful of jambalaya!

CONFESSION: For those TWC landings that I am proud of, I personally cannot manage as described above. The touchdowns are flattish, at Vapp to Vapp -3.


---- to the OP ---
busav8r: I sympathize and feel the thrill of mastering tailwind landings with F3, the art and geekiness of it, honestly I do. At the same time, may I suggest to leave that animal locked-in with a blanket over the cage? It is a skill of zero practical benefit and anyone attempting to learn it, use it, or show it off would be considered foolish by my professional idols, mostly because a chance was lost to train something meaningful to your(my) self instead.

Hope you won’t mind, let me raise one to make all of this little worthwhile: What is the PAPI MEHT for standard ICAO runways longer than 2400 m?
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Old 12th Aug 2017, 23:31   #23 (permalink)
 
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Because you've got more kinetic energy, and more downward kinetic energy (downward speed) : you should apply the flare force (lift higher than weight) for a longer time, so you should flare higher : this is as per FCOM.

So what would be your typical flare heights in headwind and in tailwind ?

My understand of the tendency to float in tailwind is that the wind will tend to reduce close to the ground, so less tailwind will increase CAS hence will improve lift and prevent the A/C from landing.
Plus in ground effect the induced drag is progressively reduced.
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Old 13th Aug 2017, 05:11   #24 (permalink)
 
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I might end up flying the A320 soon. Pls tell me it's possible to land the thing, in tailwind and headwind, without having to read the FCOM "how to land"...
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Old 13th Aug 2017, 06:05   #25 (permalink)
 
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You'll have to read it and "learn to fly again".
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Old 13th Aug 2017, 07:19   #26 (permalink)
 
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Landing without reading FCOM? Passengers are not allowed in the cockpit. You better stick to whatever you are doing,
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Old 13th Aug 2017, 08:12   #27 (permalink)
 
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With a tailwind, your groundspeed will be higher, V/S will be greater to maintain a 3 degree descent and your pitch attitude will be lower.

To achieve the same "smoothness" in touchdown you will need a bigger change in V/S and pitch. So to achieve the same smoothness you don't need "less flare" but "more flare". It's understandable that pilots will tend to flare earlier in a tailwind situation to break the increased rate of descent. Combine that with the increased groundspeed and most pilots will tend to land longer (or float).
Quote:
Originally Posted by someone
Hardly any flare is needed with a max TW. If you flare, you'll float.
"Hardly any flare" might be a good idea to avoid floating, when rwy length is a concern. The descent rate at touchdown will be higher and the touchdown less smooth. So yes, to avoid floating, "hardly any flare" seems ok but you will have to accept a firmer touchdown!

If you're aiming for a smooth touchdown on the blocks without floating in max tailwind, you will need to flare more (larger pitch change) and later then usual. (=larger pitch change in less time) =not easy.

To get back to the original question in post 1: prefer flaps full for tailwind landings.
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Old 13th Aug 2017, 09:13   #28 (permalink)

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KayPam: what a nice little bully you are. Those nubmers were posted already. Would you like to share how many 13 kt tailwind landings onto runways with LDA below 2200 m at 74 tonnes you have made in the last monsoon season?

You come across as a knowledgeable person but lately made several claims about FCOM that are not there. And seem to have missed my omisson of GSmini altogether. Maybe you can at least verify your credibility by agreening on this: it is correct to have RA callout 50' over the numbers. Hm?

172_driver Absolutely yes. Bring the aircraft to the threshold stable and on speed, keep pointing to the aimpoint. Close the TLs soon enough to prevent A/THR from kicking the N1 up once you begin to flatten the trajectory. Enjoy a second or two of adjusting the backpressure on stick, and she settles eventually between 5-3 feet. Apply the usual magic next.
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Old 13th Aug 2017, 10:11   #29 (permalink)
 
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Quote:
I might end up flying the A320 soon. Pls tell me it's possible to land the thing, in tailwind and headwind, without having to read the FCOM "how to land"...
Of course it is, although it might be wise to read other parts of the FCOM, not that its any pleasure as the distribution of information is quite bad in that damn thing. They should hire someone from boeing to show them how to write a good FCOM.

Anyway, do we really need to overthink everything? It is, despite all the noise about it being an airbus, simply an airplane in the flare. Look out the window and simply land the damn thing, (nearly) same as any other airplane.
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Old 13th Aug 2017, 14:40   #30 (permalink)
 
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Quote:
Originally Posted by FlightDetent View Post
Would you like to share how many 13 kt tailwind landings onto runways with LDA below 2200 m at 74 tonnes you have made in the last monsoon season?
Not too many I suspect as despite not even having a CPL yet he spends most of his time on here arguing jet flying...
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Old 13th Aug 2017, 16:00   #31 (permalink)
 
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Quote:
Originally Posted by FlightDetent View Post
KayPam: what a nice little bully you are. Those nubmers were posted already. Would you like to share how many 13 kt tailwind landings onto runways with LDA below 2200 m at 74 tonnes you have made in the last monsoon season?

You come across as a knowledgeable person but lately made several claims about FCOM that are not there. And seem to have missed my omisson of GSmini altogether. Maybe you can at least verify your credibility by agreening on this: it is correct to have RA callout 50' over the numbers. Hm?
I may be confusing FCOM and FCTM together, my bad.
Tomorrow and the day after tomorrow are bank holidays but maybe wednesday when I'll have access to a proper FCOM or FCTM I'll be able to quote the exact sentences.
If your companies allow you to access this documentation without being on the job.. then just look at the FCTM SOPs : landing/flare part.
It will state the normal flare height, state that tailwind conditions, ascending runway or steeper approach path require an earlier flare, etc.. There's like a whole page of it.

13kt tailwind on a wet/contaminated runway at a high mass with only 2200m of LDA seems like a bad idea. I don't have anything to run the numbers but it looks like a bad idea

tech log : as I explained earlier, I am an aviation professional, only not a pilot. Since my job is in close relationship to flying, I'm eager to learn from airline pilots' experience. And maybe I'll even correct things at my job or suggest new things if it's concluded we've been writing incorrect things.

When I said that the FCOM (or rather FCTM) states "any late flare will increase the likelihood of a hard landing" it was only to clarify things with someone here who said he was able to flare at a very low height while achieving perfectly smooth touchdowns.
Since this is in disagreement with airbus doc, either one sentence is wrong or the two sentences don't talk about exactly the same thing, so definitely something to clarify.
I'm not saying my sentence is right, I'm asking for a clarification.

There are very few airbus pilots at airbus.. Most of the guys working airbus flight ops only have a PPL or no license at all, and these are the guys writing the FCTM/FCOM.
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Old 13th Aug 2017, 16:53   #32 (permalink)
 
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Quote:
Landing without reading FCOM? Passengers are not allowed in the cockpit. You better stick to whatever you are doing,
That would be flying a Boeing then
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Old 14th Aug 2017, 00:01   #33 (permalink)
 
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Quote:
Originally Posted by KayPam View Post
There are very few airbus pilots at airbus.. Most of the guys working airbus flight ops only have a PPL or no license at all, and these are the guys writing the FCTM/FCOM.
Kay, would you mind elaborating on that one? I always assumed the FCTM and FCOM was written by Airbus test pilots. Surely the section on landing is written by a test pilot. How can it be written by a non pilot or PPL?
Just intrigued as to how it all works at AB?
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Old 14th Aug 2017, 02:56   #34 (permalink)
 
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The flight ops manual is written.. by the flight ops department.

I've taken a few minutes to find public sources for this message :
First, type "flight ops engineer airbus" and find this kind of job offers :
https://www.wizbii.com/company/airbu...s-engineer-m-f
This is an example of a job offer where it states that :
- The flight ops department comprises both pilots ("expert pilots") and engineers
- The guys who actually write the FCTM/FCOM can be interns
With these key words you can type other things in google or directly linkedin : "flight operations engineer airbus", you'll see plenty of people.
"expert pilot airbus" : much less people
These expert pilots often are ex airline TRI/TRE
But you can infer from what you've researched that there are few pilots and many engineers. Which is not surprising since it's a desk job and pilots will cost much more than engineers. (plus let's face it there are many parts of the flight ops documents that don't require any flying experience at all)

Yes you would expect the landing/flare section to be carefully proofread by several qualified pilots.
But it looks like people can go against it without major problems.
We've even read claims here that directly contradict some sentences in the FCTM.
So since (as someone said) I don't fly the bus myself I'm really not sure what's true or false. What I'm certain of is that we need some clarification on this topic.

One reason why the FCOM could appear "incomplete" is because its a very political document. If it was worded in an inappropriate way, airlines having damaged an airplane upon landing could reproach airbus with their FCTM or FCOM wording, and ask them to pay for the repairs.
The flight ops department, when they write these documents, don't think about writing the whole complete truth. Their goal is to keep airbus safe and they write things that way.
They also want to minimize incidents, like hard landings (hard landings are definetely the number one type of incident that Airbus helps airlines with)
So it's possible they'll recommend a flare height that's a bit overestimated, in order to help reduce hard landing numbers.. (longitudinal runway excursion numbers are much lower than hard landing numbers)

For all these reasons I would like an answer from your experience as pilots :
What's the lowest altitude you can start a flare and still make a proper landing ? (from stabilized conditions : -3, no wind, no stick input before the start of flare, CAS stable at VAPP)
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Old 14th Aug 2017, 07:12   #35 (permalink)
 
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Quote:
What's the lowest altitude you can start a flare and still make a proper landing ?
Depends on the airport elevation.
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Old 14th Aug 2017, 08:20   #36 (permalink)
 
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KayPam
Quote:
Most of the guys working airbus flight ops only have a PPL or no license at all, and these are the guys writing the FCTM/FCOM.
This is a ridiculous statement. A person who hasn't flown airbus is not going tell anyone how to fly one. Crosswind/wet/contaminated landings are certification issues. These are dealt with by test pilots and finalised. PPL/CPL guys may be taking dictations and putting in print.
Quote:
What's the lowest altitude you can start a flare and still make a proper landing ?
FCTM gives general guidelines. There are many variables.
Like how much seat of the pant talent you have. What is the environmental factors like wind, gust, Apt. elevation etc. But to get percentage result you should stick to standard format. If one has good judgement of the height and amount of flare you can land from any height.
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Old 14th Aug 2017, 09:04   #37 (permalink)
 
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The saga continues.
It really surprises me that seemingly experienced pilots have not noted a difference in aircraft behavior depending on:

-sharklets----float
-2 knots on top of Vapp---float
-tailwind---float

It surprises me more that people focus on the rate of descent in a tailwind. With a 2 knot tailwind there is hardly any difference. But you WILL float if you do not adapt your technique.
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Old 14th Aug 2017, 09:13   #38 (permalink)
 
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i think the point about flare heights in a tailwind is: it depends a lot on airport geography.

the FCOM is written with a relatively constant tailwind down to the ground in mind. this might not be the most occuring scenario but it is the most conservative approach as airbus would rather have a float than a hard landing as someone wrote. (how wise that is is another topic)

now it as has been commented at most airports there is a tendency for the wind to reduce substantially in the lowest 100ft. if this is the case you gain airspeed at a low level and therefore can land with a later flare.

now with all the examples we have had no one has cited an airport or actual tailwind numbers. no one has stated wind differences at low level their airports get. all this will surely influence flare height quite a bit.

to give two different examples:
- an airport somewhat surrounded by buildings or forest
- an airport on an island where the runway is nearly surrounded by ocean

that would make quite a difference regarding lower wind layers, wouldn't it?
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Old 14th Aug 2017, 09:49   #39 (permalink)
 
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A bit of raw data to feed the debate.

FCTM for long range aircraft states : "if the flare is initiated too low (below 25ft), then the pitch changes will not have sufficient time to allow the necessary change to aircraft trajectory. Late, weak or relased flare inputs increase the risk of a hard landing" (I just checked it for one airline)
FCTOM for single aisle aircraft has the same line only without the 25ft value (also checked it for just one airline)

I've seen cases in which a full back stick input from 20ft down to the ground was not enough to avoid a hard landing (for SA aircraft).
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Old 14th Aug 2017, 10:00   #40 (permalink)
 
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Kay,

Is it possible with your contacts to ask an experimental test pilot why this is so?
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