J M,
A word of caution for all, beware of assuming that ‘close to the expected weight or landing conditions’ will be OK. There are some circumstances where the dispatch margins are very small, even though the planning data appear to provide large safety factors; this is particularly so for wet runways - how wet is wet, how close to a contaminated situation, what is the condition of the tyres, type of runway surface material (beware concrete), grooves or not, brake selection, …
The wet planning data (AFM) is only a factor applied to the dry figures; there were no wet flight tests to obtain the performance and only a conservative (mid-point) assumption is used. With increasingly wet conditions, the risks in operation increase rapidly, and with a combination of effects there may be no margin at all; factored data = ALD, and thus operations require all of the flight accuracies implied in the base data.
There have been many accidents where crews assumed that the conditions were ‘close enough’, having no idea of what the actual margins were. Regulations require a pre-landing check of landing performance for all approaches; this should help crew appreciate what margins there are. A given margin should be evaluated against flight variability to guard against unforeseen flight conditions (AC 91-79 / quick rules of thumb); 5 kts fast and an extended flare can easily eat up 1500ft (airspeed deviation or change in wind). Similarly to guard against inaccuracies in the reporting of runway condition or wind, check the next worst condition, and for system failures ‘what if’, particularly lift dump, autobrake, and reverse if relied on.
And from the TALPA work, do not rely on PIREPS; these are purely subjective, depending on aircraft type and operation, and subject to error in action and reporting.
This sounds like a lot of work, but it’s what we are paid for, to be safe; and you can tell the judge after the event. A full evaluation for every landing should help build knowledge of actual landing performance for the conditions, particularly for the more junior pilots. In every debriefing ask – ‘where would we have stopped, what was the achieved landing distance’?
Merry Christmas, and I hope that Santa will not miscalculate landing distance.
Managing the Threats ...”