Dispatch V inflight

[fidelio]

Hi

Can someone enlighten me as to what dispatch and inflight are when you are doing landing distance calculations, and why there is a difference between the two? I fly Airbus and use fly smart software for performance. Am I correct in thinking dispatch is more of a regulatory thing and is more conservative than inflight? Ie... Inflight likely to give you shorter LDRs?

Thanks

[Fly3]

Dispatch usually will calculate limiting weights while inflight or en-route in the case of the B787 will calculate distances I believe.

[FlyingStone]

To be able to dispatch an aircraft, it needs to be able to land within 60% of LDA at destination and alternate(s) at the estimated landing mass.

Once you are inflight, dispatch conditions are not applicable anymore and the only requirement is that LDA is greater or equal to ALD (actual landing distance for the given conditions). Most companies have a 15% safety margin for in-flight landing distance assessments, which is also implemented in Airbus performance software.

[Skyjob]

To be able to dispatch an aircraft, it needs to be able to land within 60% of LDA at destination and alternate(s) at the estimated landing mass.

Once you are inflight, dispatch conditions are not applicable anymore and the only requirement is that LDA is greater or equal to ALD (actual landing distance for the given conditions).

From a planning point of view if runway length is limited at destination, it may this be required to (fuel) plan to fly to an alternate with a longer runway and take that plus satisfy all legalities of diversion fuels from there onwards if higher then destination requirements, as landing cannot be assumed at planning stage at destination. Think of it as planning for two alternates.

[safetypee]

This has been debated many times before with a range of views, transatlantic and EASA operators.
I wonder if it is reinterpreted against EASA’s IR-OPS there would be any revised views.

CAT.OP.MPA.300 “should not prevent a safe approach, landing or missed approach, having regard to the performance information contained in the operations manual.”

CAT.POL.A.100 requires the use of “approved performance standards that ensure a level of safety equivalent to that of the appropriate chapter.”

CAT.POL.A.105, “performance data contained in the AFM shall be used to determine compliance” This appears to contradict OP.MPA.300.

CAT.POL.A.230 Landing — dry runways
“The landing mass of the aeroplane determined in accordance with CAT.POL.A.105(a)” i.e. AFM. See conflict with MPA 300.

“ for turbo-jet powered aeroplanes, within 60 % of the landing distance available (LDA)” 1.67 factor

e) For dispatching the aeroplane. … the 1.67 above applies (note wet adjustment, 1.92, below).

CAT.POL.A.235 Landing — wet and contaminated runways
“(a) … may be wet, the LDA shall be at least 115 % of the required landing distance, determined in accordance with CAT.POL.A.230.” 1.92 factor

“… may be contaminated, the LDA shall be at least the landing distance determined in accordance with (a), or at least 115 % of the landing distance determined in accordance with approved contaminated landing distance data or equivalent, whichever is greater.” Methods for providing contaminated data are given in AMC CS 25.1591, recommended reading for the operational limits and assumptions.

Conclusions? Use AFM data unless there is specifically approved landing data is in the Ops Manual, (FCOM, QRH)
For takeoff use 1.67 / 1.92 based on the AFM.
For landing use AFM or alternative approved data which provides equivalent safety. Noting that most Ops Manual data allows credit for reverse, but it’s not clear how this can be related to the non-reverse AFM data to show equivalent safety, or how the 1.67 / 1.92 factors (CAT POL A 230) should be applied or not. One view is that the new Airbus (OLD/FOLD) performance, with more realistic landing distances, plus 15%, provides equivalence with the AFM; but is this factored or un-factored AFM data?

What do operators actually do?

[Mansfield]

In the States, FAR 121.195(b) requires you to plan to arrive at a weight which allows allows a full stop landing within 60% of the effective runway length. FAR 121.195(d) says that if runway conditions at the destination are expected to be wet or slippery, you must ensure a runway effective length that is at least 115% of the length you needed in paragraph (b). Since, presumably, the runway hasn't changed in length, this leads to a weight reduction. The change in terminology between the rules has always led to confusion. It would be much easier if para (d) simply repeated the requirement of para (b) and replaced 60% with 52%.

Operations Specification C054 used to say that the pilot could not begin an instrument approach if the reported visibility was less than RVR 4000 feet or 3/4 mile unless the runway length was equivalent to 115% of the length required by 121.195(b). This was more restrictive than the flight planning requirement, because it was effective at the time you began the approach.

C054 has been changed in recent years, at least at my airline (and since OpSpecs are essentially boilerplate, I suspect this is pretty standard). Now it says that if the forecast calls for a visibility of less than RVR 4000 feet or 3/4 mile at the time of takeoff, then a runway length of 115% over that required in 121.195(b) must be available. This is interesting because I have never seen a forecast containing a reference to RVR. They have simply cut and pasted the original reference to basic turbojet landing minimums into a new planning requirement. In any event, now you need to consider both the wet or slippery criteria from 121.195(d) and the visibility requirement from OpSpec C054 as planning requirements; both trigger the 115% criteria.

But...you no longer need the 115% criteria to begin the approach. Nowadays, OpSpec C054 has a new requirement which says that:

If un-forecast adverse weather or failures occur, the PIC shall not begin the final approach segment of an instrument approach unless the runway length needed for landing is determined prior to approach. The runway surface composition and length, reported runway and weather conditions, AFM limitations, operational procedures, and aircraft equipment status must be considered.

We have a landing distance assessment table that essentially provides six columns separated by braking actions: Under the column titled "Dry" they provide AFM data to satisfy the requirement of 121.195(b). Under "Good" they provide AFM data to satisfy 121.195(d). Neither of these columns have a penalty for inoperative reversers, because, of course, reverse is not credited in AFM certification data for dry runways. The remaining four columns, "Good to Medium" through "Poor" provide manufacturer's advisory data for the respective braking actions. These number only allow for a 15% margin, as opposed to the 67% margin for 121.195(b) and and the 92% margin for 121.195(d).

So, as the runway conditions worsen, we just get rid of a big chunk of margin. No problem.

The old Advisory Circular for this, AC 121-195(d)-1A from 1990, states the following:

In determining safe operational runway lengths that provide for operational variables not included in type certification tests, FAR § 121.195(b) requires a runway length adequate to allow a full-stop landing (based on the type certification tests) within 60 percent variables include deterioration, of the runway atmospheric effective length surface conditions, instability of the piloting such as gusts runway. The techniques, operational tire and brake or windshear, crosswinds, others.

FAR 5 121.195(d) operations into wet or approach to touchdown, flightpath deviations, and requires an additional 15 percent runway length for slippery runways.

What we have done in response to the serious problem of landing overruns is to a) remove the requirement for a 92% margin in runway length in order to initiate a low visibility approach, and replace it with a requirement to evaluate the runway surface conditions, equipment limitations, etc., and then, b) provide non-certification data with no margins to protect against the same operational variables specified in the Advisory Circular.

I sense a serious loss of old, established knowledge in the re-writing of these requirements, but there you have it, as best as I can see. I'd certainly be interested in anyone else's interpretations. I realize this is not applicable to other parts of the world, but since we are all trying to harmonize, some of this may be bleeding across borders...

[LeadSled]

http://www.pprune.org/tech-log/572178-take-off-alternate-landing-distance-req.html

Folks,

There is already a thread covering much the same.

The operational length you require will NEVER be 60% of AFM or 60% of AFM plus 15%.

Note in particular my last substantive post, making the point of what the law currently is, in both FAA and EASA Land, versus the confusion re. advisory information, and all sorts of "good stuff" coming down the pipe, but NOT AUTHORISED BY LAW, yet!!

Wherever, whenever, the minimum landing field length required is the AFM figure, where the actual ( test pilot) demonstrated landing field length is 60% of the AFM length ---- but it is the AFM that is the minimum, specific Ops. Spec. requirements or regulation may require more.

When the method of establishing AFM landing field length changes, the results will seldom be less than the current figure, and frequently more.

As an example of the latter, the +15% on AFM for wet runways will no longer be at the discretion of the PIC, and it may be more than the present AFM + 15%.

Tootle pip!!

[safetypee]

LeadSled, I have difficulty following your points on required length and differences between AFM and Ops Manual/FOCM/QRH data.

Is required length being intermixed with achievable/actual length?
The requirements for required length are stated in IR OPS.

You imply that AFM actual is the same as Ops Manual actual; I don’t believe this is so.

For all practicable purposes the AFM actual landing values cannot be achieved in operation; factors are applied as per IR OPS for dispatch.
Depending on the interpretation of IR OPS, AFM data could be used for landing with some factoring, not 15%, more likely the full ‘take-off’ factors – equivalent safety. Most operators use Ops Manual data.

Existing, legacy data - the manufacturers’ and Ops Manual “actual” distances, are greater than those in the AFM, primarily because of the increased air distance. However, because reverse may be considered, some distances appear to be less than the AFM. This difference represents the increased risk associated with reverse (failure/selection) which operators should consider.
Although this data is more representative of what might be achieved in operation, for practical purposes the addition of a minimum of 15% is a better estimate of the minimum achievable distance based on operational practice. FAA use this as advisory, IR OPS a requirement.

Many of the problems above were identified by the industry, enhanced by the Midway accident for contaminated operations, which resulted in TALPA. TALPA amended the calculation and reporting of braking action, this was agreed and is probably acceptable for ICAO. Europe plans to implement this as ‘law’ across the various agencies involved; at best the FAA remains advisory - with changes.

Manufactures at TALPA agreed a new basis for preparing landing data which would provide even more representative distances for operations, covering a range of conditions; this uses the runway condition reporting format above.
Europe had already provided a basis for calculating contaminated data, CS 25.1591, which ‘legally’ meets the requirements of IR OPS, but noting that any increased risk in contamination operations has to be mitigated – exposure/frequency and training (IR OPS, but not FAA).
The new calculations provide Operational Landing Data (OLD) or when factored FOLD, this will be greater than previous ‘actual’ data. Europe plans to have, or has this in their requirements, but the FAA action at best will be advisory.
Airbus has published landing data, but it is uncertain which other operators have published.

[LeadSled]

Safetypee,
I am not confusing anything, perhaps I could have expressed it more clearly, so I will try again. Also read what I said on the original thread.

The LEGAL minimum landing field length, whether for planning or inflight purposes, is the AFM figure, until such time as the certification standard changes.

That AFM figure is the "demonstrated length" factored by 1.67, or as more commonly expressed ( to the evident confusion of many) the demonstrated length is 60% of the AFM length.

There has been much discussion about the new certification standards, but they are a long way from FAR 25 just yet, and EASA had stated it will follow FAA, see the Trans Atlantic Mutual Co-op. Agreement.

Airbus in particular has published lots of "good stuff" that approximates how the "new" system (actually not new at all, but a refinement /development of the 1960s BCARs) will work.

As far as I can determine, Australia is the only country that has revised some regulations to "apparently" authorise the "new" way of doing business.

However, looks like there is a serious shortcoming there in legal terms,( not surprising, we do great job of screwing up new regulations) the AFM landing filed lengths have not changed, because the AFM certification has not changed, and Australian C.of As ( and hence AFM) must conform to the state of origin C.of A. Indeed, our CAR 138 required compliance with manufacturer's AFM.

In a practical sense, if not a legal sense, what Australia is doing is not an operational problem, because the "new way" (in fact using Airbus ADVISORY information) never throws up a figure less than the present AFM number, and often it is (wisely) much greater, depending on the degree of and type of contamination expected.

So, if you have some kind of dispatch system, or Operations Manual, that comes up with figures less than the AFM, that system/manual is wrong.

It seems reasonably clear that there is also much confusion in EASA Land, it looks to me like the bureaucrats have confused themselves, because the various document you quote are NOT certification documents, and the AFM figures have not changed, and there is clearly (to me) a legal conflict. Again, in the real world, the numbers you come up with will not be less than the current AFM figures.

However, I would not like to defend my use of the "new" system, in the event of a serious incident or accident (even if the cause for the inquiry is not related to the above issues), particularly any inquiry in Greece, Italy, Spain or France.

Tootle pip!!

[Denti]

Hard to check AFM distances here, our AFMs do not contain landing distance figures anymore, they just point to an engineering software which of course is not the software we use on the line.

[LeadSled]

Denti,
A full AFM for a large aircraft has never been made available for crews, as far as I know, so you are dependent on the extracts of data provided to you.

I once saw the complete performance data for a B747-200/300 from the AFM --- just the performance data -- which is the largest section of the whole.

I don't know exactly how many volumes there were, in the then Boeing standard US A4 sheets, in a binder about 3 inches thick, but it covered a whole wall that I would guess as about 3-4M wide, and about 1M high --- must have been 50 volumes.

I was glad to leave the detail to the company performance engineers.

The more I look into this, the more of a technolegal quagmire it becomes.

The idea is good, the execution is ????? pick your own description.

Tootle pip!!

[safetypee]

LeadSled (#9) I prefer to use 'requirement' opposed to ‘legal’; requirements can either have a legal or advisory basis.

I agree that the requirement for the minimum landing field length is 60%, applying to both dispatch and inflight. However, whilst dispatch requires the use of AFM data, it is less clear that the AFM data has to be used in flight -
See the conflict between CAT.OP.MPA.300 – Ops Manual, and CAT.POL.A.105(a) – AFM, but CAT.POL.A. 100 does allow ‘approved performance standards that ensure a level of safety equivalent to that of the appropriate chapter’.
Assuming a top–down precedence, then ‘other approved performance data’ could be used for landing (EASA) – I cannot find an equivalent for the FAA or Australia.

I cannot identify any relevant changes in certification standards (CS 25 aircraft), and whilst the operational requirements (EU IR OPS) continue to evolve, this is apparently without significant change in the actual requirements. However, the landing data and methods of calculation which can be used to meet the requirement (as approved by the regulator) has undergone significant change, e.g. introduction of contaminated data and thence to OLD/FOLD. These can be, or are considered as ‘other approved performance data’; hence the widesperad use of Airbus FOLD.

Whilst there is an agreement to harmonise FAR 25 and CS 25 (aircraft) this does not mean that EASA is following FAA; some differences exist, e.g. CS 25 already has requirements for contaminated data, FAA has not.
For operational requirements, FAA part 121 vs EU IR Ops, there are significant differences, generally where the FAA is lagging due to a backlog of ‘law making’, thus the use of ACs.

I agree that OLD/FOLD should give a longer required distance than the AFM due to the method of calculation.
In Europe it appears that FOLD is generally accepted as ‘approved performance data’; the FAA also appears to be following this; see AC 25-32 “11.3 Contaminated runway landing performance data approved by either the Joint Aviation Authorities or EASA in compliance with either their contaminated runway type certification or operating requirements are acceptable when using the optional process identified in this AC, …”

[john_tullamarine]

A full AFM for a large aircraft has never been made available for crews


LS, not quite correct for Oz. As I understand, you were a QF man.


Oz regs have always provided for a concession not to carry the AFM provided that the data is included appropriately in the Ops Manual. The majors have always used this with the (expensive and legally authoritative) AFM documents being maintained in the Ops Eng cell.


Refer CAR (1988) 54 and 139(3). Stretching the memory, back in the olden days ... ANR 113(3) preceded 139(3) .. can't recall the 54 equivalent but it was there as well.


That is, each aircraft still has its own approved AFM and, per regs, it is required to be carried in the aircraft unless the concession applies.

[Mansfield]

While I have been aware for several years of the difference between Boeing’s certification and advisory data, I have just in the last few days been reading all of your posts both in this thread and in the previous thread referenced by Leadsled. This has, I hope, brought me sufficiently up to date with the output of TALPA and so forth. Now the question is, how to implement the new FAA landing distance assessment requirements with the data provided by my company for my airplane, which is an MD80.

As I indicated in my previous post, it appears to me that a great deal of the old regulatory margin, intended to protect against average risk, has been disposed of in favor of more precise identification of several specific risks such as runway slope and additional speed additives, etc. I understand that the regulatory requirements for dispatch remain. What I am trying to do is make sure I understand what is going on with the implementation of the TALPA output.

To better understand this, I have attempted to dissect the numbers in my performance manual. I’d like to float an example here and see if anyone with a better understanding of this can provide a course correction to my thinking.

At 130,000 lbs, my MD80 has a Vref of 132 KIAS. The dry certification landing distance, at sea level, etc., is 5030 feet. I can remove the regulatory factor from this by dividing by 1.67, which yields 3011 feet as a raw, flight test landing distance.

Just taking an educated guess at what the air distance might have been during this certification, I cranked through the equation in AC 25-7A for a calculated air distance at 132 KIAS, and that yielded 1121 feet. I have no idea whether that is the actual air distance associated with the actual flight test data, but it should serve as a reasonable assumption.

If we go back to my dry distance of 5030 feet, I could, in theory, be dispatched to a 5100-foot runway. This runway would have a touchdown zone of one third the runway length, or 1700 feet. Policy says that I must touchdown within that touchdown zone or go around.

If I fly this approach exactly as a test pilot would, with the single exception being that instead of an 1121 foot air distance, I use the entire touchdown zone, I end up using an additional 579 feet. Consequently, my flight-test-quality experiment gives me an actual landing distance of 3590 feet. This is still well within the LDA; the 1.67 factor has accommodated my float across the touchdown zone pretty well.

Now I went back and tried this same process with the advisory data that I have in my performance manual. Same weight, same Vref, but I selected the first column of “FOLD” data…we don’t yet call it that, but that is what I assume it is. So, for good-to-medium braking action, I get a FOLD of 7620 feet.

Next, I remove the factor, in this case dividing by 1.15. This gives 6626 feet.

In order to arrive at an estimated air distance for this condition, I simply assumed that I would spend 7 seconds at 132 KIAS before touching down, which yields 1559 feet.

Next, I assumed a limiting runway for this condition, which would theoretically be 7700 feet. One third of this distance yields a touchdown zone of 2566 feet. The difference between the estimated air distance and the full length of the touchdown zone is 1007 feet. If I add this to the unfactored OLD of 6626 feet, I get a landing distance if 7633 feet…67 feet short of the end.

If I repeat the same experiment with the straight “medium” braking action data, I end up 14 feet past the end of the limiting length runway of 8100 feet.

So it seems to me that a policy-legal landing at the far end of the touchdown zone uses up the entire 15% margin without anything else going wrong. The operational variables cited in AC 121-195(d)-1a include “piloting technique” and “flight path deviations” as part of the reasoning for a 67% dry margin. Yet in all of the reading I’ve done lately, including SAFO 06012 and AC 91-79A, I see a lot of discussion regarding the use of deceleration devices, etc…but no discussion regarding piloting technique per se, outside of an enormous get-out-jail-free card for the authorities that mentioned operator training and experience.

Indeed, it seems to me that, assuming a runway-limited situation, that the test-pilot precision that we all agree is not representative of line operations is exactly what will be required to make these new numbers work.

What am I missing?

[donstim]

Well, let's see. Without even discussing any errors in your assumptions, you cite a FOLD of 7620 feet for a wet or slippery runway for which the "old" method would have allowed landing on a 1.15*5030 = 5785 feet and you question whether the FOLD provides increased safety?

[safetypee]

Mansfield, an interesting analysis; like donstim I suspect that the problems, if any, are in the assumptions – yours, the operator, the regulator.

You refer to the performance manual for certificated data (Cert) and in the same manual, advisory data (Adv).
Is the Cert performance exactly the same as the AFM Certificated data? i.e. dispatch is based on Cert, and landing on Adv.
In my experience your assumed Cert air distance is too much; note that Boeing North use 1000ft in their ‘actual’ data, thus Cert is probably less than that. However your calculations may still be reasonable when adding in the time delays in selecting the retarding devices. Thus the no-reverse brakes on-to-stop distance is just less than 2000ft; is this distance reasonable? Or is this more compatible with using reverse – the implication being that the perf manual dispatch case is based on Adv.

IMHO the discussion of landing in touchdown zone and assumed use of factors is a misinterpretation of the safety process; more on this later. However, because this has been applied to both cases, then the math may not be affected.

A crucial assumption is that your Adv is based on OLD/FOLD; I have not seen any ‘TALPA’ data from Boeing, although it is reported that it is available for newer types.
If your Adv is still legacy information, then why should there be a difference as in your calculations?

The information in https://www.scribd.com/doc/298104136/Boeing-Slippery-Runways-Notes indicates that the basis of the ‘actual’ Adv data is with reverse (pages 5-8). The (misleading) graphical representation indicates that the ‘actual’ landing distance is similar to the factored Cert distance; i.e. the increased air distance being more than counterbalanced by reverse. Noting that this is a Boeing north presentation vs your Boeing South aircraft.
Operational evidence suggests that the approximate equivalence in the data sets (gross assumption) has enabled the use of Adv to meet the landing 60% landing requirement i.e. there are no other safety factors in the use of Adv. Thus SAFO 06012.
I sense that at this point there are weaknesses in my interpretation.

If the Adv (operational min with reverse) is not equivalent to the Cert (absolute min flt test x 1.67) – as depicted by the ref, this may affect the assumption that your FOLD includes a 1.67 factor. AFAIR all Airbus references to OLD do not include the 1.67 factor, and that FOLD only applies the minimum 15%.
Thus my suspicion is that your Adv may not be based on TAPLA.

What have I overlooked, assumed, missed?

Re the implication that landing in the touchdown zone - first 3000ft will be ‘safe’, is very misleading.
1. FAR/CS 25, and FAR121 Cert define a level of safety (without reverse).
2. FAR 121 and IR OPS require a safe operation - landing, where (unspecified) factoring is assumed to be sufficient for the everyday variability in operation. This could provide an equivalent level of safety as 1, but the baseline data and factors may not be the same as 1, thus who chooses which data to use and the factors; regulators or operators.

Where safety factors are considered as a margin for unseen (uncontrolled) variability in operation, then a limiting landing distance would not have any further margin beyond that assumed in the data, i.e. pilots will land with 1000ft air distance, speed, etc, - a normal landing plus a safety margin to accommodate unforeseen aspects. Unfortunately many normal landings appear to eat into this margin.

However, if the safety margin is considered as part of normal operation (land within the first third, etc), this will reduce the safety margin for the unforeseen, thus the overall operation would not provide an equivalent level of safety as might be assumed by the landing data.
Who provides the interpretation of landing zone – no universal definition? Some aspects of regulation are based on distance, others on a more practical landing zone; similarly with operators – confusion reigns.
I suspect that any interpretation will be applied after an event and that it will be the regulators who will get-out-of jail for free!


For an Airbus view http://www.ukfsc.co.uk/files/Safety%20Briefings%20_%20Presentations/Airbus%20Safety%20First%20Mag%20-%20August%202010.pdf (page 8)

and

http://www.scribd.com/doc/62707861/Safety-First-12 (page 5)

[Mansfield]

Safetypee, many thanks, particularly for the link. That presentation is very similar to the one I have entitled “Landing on Slippery Runways” by Paul Giesman and Jim Ratley of Boeing, but it always helps to see similar graphics in more than one presentation. Both presentations attempt to depict scaled comparisons, in which the medium braking action distance, unfactored, comes in just under the wet cert distance. This is not the case with the MD80 data that I have. However, I looked at our company data for both the 737 and 757, and it is indeed exactly that way. This might be a Boeing North/South thing, but it also occurred to me that the MD80 cannot crack the reversers until the nose is on the ground, whereas aircraft with sleeve type reversers can. Additionally, the MD80 is limited to about 1.3 EPR in reverse, lest one blank the rudder a' la LaGuardia last winter.

My operator provides us with a table containing six columns. (No AFM in the States…ever). The first two are titled “Dry” and “Wet” and contain no correction factors for inoperative reverse. According to the textual description in the performance manual, these two columns represent the cert data, and the text specifically refers to the respective factors, i.e., 1.67 and 1.92.

The next four columns are titled, “Good to medium”, “Medium”, “Medium to Poor”, and “Poor”. This is in alignment with the RCAM. The textual description for these columns claims that these data are based on the manufacturer’s estimated landing distance, plus a 15% factor, using normal reverse, Vref+5 knots and a 0.5% downslope. We also have the corrections for approach speed, winds, temperature and no reverse. The description further states that the air distance is predicated on 7 seconds at Vref. These descriptors lead me to believe that this approximates the TALPA template.

The raw data provided is very useful. The more-or-less linear progression of distance numbers across the page, from the dry column, to good, to good-to-medium, to medium, etc., suggests a linear increase that appears pretty logical. If you understand why the first two columns contain no factor for inoperative reverse, and the rest of the columns do, you’re one step ahead. However, it is only in the fine print that the rather substantial shift in safety margin is explained. Even then, the check airman who gave me my LOFT last week was under the impression that all of these numbers included the 1.67 safety factor.

The range of touchdown for narrow-body aircraft is typically stated as between 800 and 1500 feet beyond the threshold. The touchdown zone, of course, is defined (and illuminated) as the first one third of the length, up to 3000 feet. Policy is very clear that a go-around must be initiated if one has not touched down before floating across the touchdown zone. Safetypee’s two examples of how one uses the safety margin highlight how we seem to straddle these criteria. In other words, the 800-1500 foot target is designed to reserve the margin for other happenings, while the go-around policy tolerates some use of the margin in normal operations. On most 12000 foot runways, either one works seamlessly and invisibly.

Until we get to a runway limited case with less than optimum braking action. The certification margins are huge. The consensus seems to be, and is certainly recorded in much of the literature, that such margins are necessary because line pilots cannot duplicate the profile flown by the test pilot. I disagree to some extent with that notion, although not entirely. Most of the test pilots I have known are pretty good pilots, but I’m willing to bet that many of us who fly three or four legs a day every day can do some fairly precise flying as well. On my commutes to work through Washington National, for example, I see almost everyone, from the old salts to the fresh-faced kids, hit the thousand foot mark almost every time, even coming off the turn following the river visual.

Rather, the large margins in cert exist to protect against a wide range of possibilities, which is essentially an average risk approach. Looking at how the Boeing medium braking action raw data still appears to be less than the wet dispatch data, it occurs to me that this large margin, average risk approach has served a bit too well over the years, masking some nasty realities regarding actual braking coefficients and so forth.

So now we have much better data regarding the actual braking conditions. At the same time, it seems to me that we have shifted from a large margin, average risk approach to a narrow margin, specific risk approach. Through the use of approach speed additives, the RCAM, temperature adjustments, slope corrections, etc., we are tweaking each specific risk that we can identify, and therefore justifying a substantial reduction in the applied safety margin. There is likely a good argument for this change, both economically and from a purely safety point of view. However, it is a substantial change in philosophy that does not appear to be articulated at all.

As Safetypee points out, many normal landings eat into the old margin. No one notices because the margin is huge and most runways are long. But we can’t have a policy that allows you to continue trying to land as long as you are over the touchdown zone when half of that touchdown zone comprises your entire safety margin.

[safetypee]

Mansfield, thanks for the additional explanation.
I agree with your interpretations of the data, but it might be worth checking with Boeing for TALPA confirmation.

Re non effect of reverse; there may be an explanation on slide 31 of the Boeing presentation – ‘reverse may be additive’; or without rev, auto brake 2, and low braking action, then because the decal target cannot be achieved the distance will be longer, but with better braking action, this is not so.

Your earlier question “how to implement the new FAA landing distance assessment requirements” is the critical aspect in the discussion.
I am ‘old school’ UK, where landing data was interpreted as requiring factors as per dispatch (equivalent safety), and that ‘safety margin’ was considered as in #16. The background docs are below.

In more recent times, the focus has changed towards ‘actual’ landing performance (FAA always has?) and the risks on contaminated runways. It appears that the requirement for landing within 60% of the runway has been reinterpreted (see #16 regulatory precedence EASA?) or alternative applications (FAA?).
Europe, specifically the UK, promotes a ‘clear runway’ policy and additional risk management for unavoidable contamination. Although the risks may be higher, less safety margin, they could be ‘acceptable’ providing the frequency of operation is minimal and the landing accuracy is improved - there is no acceptable ‘landing zone’. Both of these require operator/pilot judgement which may be eroded with time; wet/contamination landings (data) become the norm because of commercial, airspace, runway usage pressures. The EASA certification requirements are in AMC CS 25.1591, which provides ‘chilling’ operational advice – apparently without any need for operators to heed the CS 25 warnings – or even read them (~page 864).

For thought:- If FAA had required fully factored landings, then why issue SFO 06012?
Similarly for EASA; or if the full factors are a landing requirement then why does the industry need FOLD?

“… we have shifted from a large margin, average risk approach to a narrow margin, specific risk approach’.
Yes; previously some authorities implied a large landing margin, the FAA less so. Now regulators place greater responsibility for assessing and managing the risk on operators, and particular the crew.
For this they require greater knowledge and better regulatory guidance, including regulatory interpretation, which is sadly lacking or at best confusing/conflicting. E.g. certification landing performance is based on air distance with little margin, on which actual distance is based; but operational regulation only recommends a small factor yet discusses a much greater landing zone.

Thus “how to implement the new FAA landing distance assessment requirements”; we should always add more than the minimum 15% margin, and for any wet or contaminated runway use the next lower reported braking action SAFO 15009 (www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/safo/all_safos/media/2015/SAFO15009.pdf) and review the Boeing tech bulletin; landing on slippery runways (http://vipa.asn.au/sites/default/files/pdf/member/130923%20tech%20bulletin%20slippery%20runways.pdf), MD 80 similar.
Review the policy and wording of advice and requirements on ‘landing zone’.

Refs
Old School, but may be current.
AIC 14/2006 LANDING PERFORMANCE OF LARGE TRANSPORT AEROPLANES (www.ead.eurocontrol.int/eadbasic/pamslight-538CEB5575AACE67347F585293A99A73/7FE5QZZF3FXUS/EN/AIC/P/014-2006/EG_Circ_2006_P_014_en_2006-02-02.pdf)
AIC 86/2007 RISKS AND FACTORS ASSOCIATED WITH OPERATIONS ON RUNWAYS AFFECTED BY SNOW, SLUSH OR WATER (www.ead.eurocontrol.int/eadbasic/pamslight-538CEB5575AACE67347F585293A99A73/7FE5QZZF3FXUS/EN/AIC/P/086-2007/EG_Circ_2007_P_086_en_2007-09-13.pdf)
Operations on Contaminated Runways Safety Notice 2011 016 (www.theairlinepilots.com/forumarchive/quickref/caacontaminatedrunways.pdf)

Current EASA
Review of aeroplane performance requirements for CAT operations (https://easa.europa.eu/system/files/dfu/ToR%20RMT.0296%20%28OPS.008%28a%29%29%20-%20Issue%201.pdf)
CS 25 Certification Specifications and Acceptable Means of Compliance for Large Aeroplanes (http://easa.europa.eu/system/files/dfu/CS-25%20%E2%80%94%20Amendment%2017_0.pdf) (~page 864)
Airbus view of TALPA 2010 (www.scribd.com/doc/298396379/AIRBUS-Perspective-OLD)
and Workshop Runway Friction and Aircraft Braking | EASA (http://easa.europa.eu/newsroom-and-events/events/workshop-runway-friction-and-aircraft-braking)