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...-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%...ust%202010.pdf (page 8)
and
http://www.scribd.com/doc/62707861/Safety-First-12 (page 5)