Re Boeing data usually doesn’t include the 1000ft+ from threshold to touchdown
Can you cite any objective evidence to support this claim ? (#17)
JT at that stage of the thread it was unclear if the unfactored distance quoted included the airborne distance. My statement was poorly worded and it would have been better to ask a direct question.
I have rechecked a 737 ‘Classic’ QRH and the unfactored landing distance tables do include 1000ft airborne distance.
However, I note that the total distance quoted includes 'detent' reverse and thus is not the same basis as for factored landing distances. The details are in the QRH ‘small-print’.
This suggests that the factored distance quoted (9500ft) could be considerably less than would have been calculated with ‘dispatch’ rules using certificated ‘unfactored’ data (no reverse).
A more practical view of the importance of ‘airborne distance’ in determining the actual landing distance, comes from a FDM / FOQA report (SESMA; 12000 landings, 737-400), which shows an average touchdown point around 1000ft beyond the GS location, i.e. about 1900ft beyond the threshold. The report also showed that the median speed at flare height (30ft) was Vref+7. Thus operators should consider adding at least 1000ft to their estimates of actual landing distance.
This addition is also reflected in the FAA advice in SAFO 06012 “The airborne portion of the actual landing distance (distance from runway threshold to touchdown point) should reflect the operator’s specific operations, operational practices, procedures, training, and experience.
Another point is that if the operator’s procedures require full reverse, yet reverse is not credited in the aircraft’s certificated landing data, then landing risk increases due to the probabilities of incorrect selection and operation of reverse. Here (again), operational rules appear to conflict with aircraft certification rules. The SAFO defines both Unfactored Certificated Landing Distance and Actual Landing Distance, the latter better representing flight operations and not theoretical minimums.
In addition, on a dry runway and when required for non-normal landings, crews should always use max manual braking with full reverse. With autobrake, when the deceleration target is reached the contribution from the brakes is reduced, the commanded deceleration is then maintained by a combination of reverse and reduced braking, which is not max deceleration, thus the landing distance is longer.