misd-agin the touch-down point is an important factor (#232), but so too is the speed at the threshold as this contributes to higher energy and an extended flare.
I assume that you refer to the difference in distance shown in the performance manual, which relate to landing at the correct speed but at different weights (at the correct point); thus this difference may not be representative of an over-speed landing.
If the aircraft lands fast with respect to the correct speed for the weight, then there is a distance increase due to the energy and the long touchdown point from the extended flare.
AC 91-79 gives an example of such an event where typically a 10 kt speed excess increases the landing distance by 500 ft, but the extended flare contributes a further 2500 ft (3000 ft total). The touch-down point part appears dominant, but it originates from excess speed.
Given these figures as representative of the Jamaica 737 landing, then with the additional hazard of the tailwind, a touch-down point at 4000ft down the runway may be easier to understand.
I do not agree with the view expressed by p51guy I think pilots are fully aware of the runway they need. (#221).
The landing data supplied by many operators only shows the maximum landing weight (MLW) for a runway in specific conditions (wet/dry, wind, alt, etc). Many crews only check that the actual landing wt is within limits (‘we’re legal’ syndrome), whereas a more circumspect crew might asses the actual wt as a % of MLW and judge the required level of braking, but in either case, not checking the actual or required distance.
Greater professionalism might result in checking the actual distance charts and applying a factor, considering previous operations – experience, or by adding a safety factor for items not considered by the data.
For those aircraft with auto brake / distance charts, the data is only as good as the assessment of the runway conditions, which is also a major weakness in the crew’s situation assessment and decision to land (see #217).
Regulated landing performance has a safety factor, but the often quoted 1.92 (wet/jet) value is most unlikely to be achieved. A significant proportion may used up in the difference between a ‘certification’ minimum distance landing and that routinely practiced in every-day operations. Furthermore the data assumes a level of friction appropriate to wet conditions, but how wet is ‘wet’ – what are the exact conditions on the runway.
Manufactures rarely fly certification wet landings; the wet performance is based on dry landings and an assumption about the runway condition. Overall the safety margin during a wet landing is probably less than that for a dry landing.
After considering other distance reducing factors such as runway texture, wind error, contaminant (rubber, paint, dust), none of which are in the performance data, the overall safety margin could be very small.
Thus pilots must strive for accuracy during the approach and landing, taking responsibility for both the judgement to land and the execution of the manoeuvre. There is no hiding behind ‘legal requirements’.
It is the pilot’s professional duty and responsibility to form and adjust a plan for a safe result – taking hindsight and turning it into foresight.
The Jamaica 737 landing might have been ‘legal’ – the plan apparently met the requirements, but due to any one or a combination of the many possible errors, misjudgements, or malfunctions, the execution of the plan and thus the result was incorrect.
Considering what can be done whilst we wait for the investigation report, the following questions may be worthy of debate:-
Why didn’t operators know that the runway was contaminated with rubber (slippery when wet), or what precautions to take with that knowledge.
How do pilots report these conditions to the authority? Similarly for poor runway draining characteristics.
Do operators take account of the non-existent RESA? Are operators landing distance charts adjusted to allow for this?
Do operators specify additional approach / landing accuracy for difficult or ‘limiting’ runways – and mandate a go-around?
Do crews adjust landing distance for increased Vref (gust factors)? If so, how; - not knowing the required landing distance (as discussed above)?
Finally, and perhaps a major concern in the industry, is that there appears to be too many open questions about marginal landing conditions.