AA Crash Jamaica

[PEI_3721]

The certificated landing distance, which is the basis of operational factored landing distances, may have credit for reverse thrust if the system is sufficiently reliable (FAR/CS 25.125 –“means other than wheel brakes – if it is safe and reliable … consistent results … without exceptional skill”).
Information in the Boeing presentation Landing on Slippery Runways (slide 15) indicates that for the 737, reverse is not credited in certificated data.
Note that for EU operations on contaminated runways, reverse thrust may be considered when calculating contaminated data (CS 25.1591); AFAIK, there is no FAA equivalent regulation. Also, note that contaminated data have significant reductions in safety margins when compared with normal landing data.

I believe that the ‘737 landing tables’ (BOAC - #520) are the QRH actual landing distances, which Boeing refer to as ‘advisory’. If crews use this data with factors, the resultant distance may not be the same as the certificated data because they have differing assumptions and criteria. As stated, the advisory data uses reverse detent, and also assumes a fixed flare distance from the threshold to touchdown.

One possible area of ambiguity is in any difference between what is required for dispatch (fully factored certification data) and that required by a prelanding check.
If for the prelanding check crews use the advisory data and factor this by the ‘in flight’ minimum (1.15) as indicated in FAA SAFO 06012, then as above, the result can be a different and much shorter distance than that required for dispatch.
In many instances, this shorter distance may only represent the absolute minimum that an average crew can achieve with accurate approach speed, ideal touchdown position, and max brake in the conditions specified.

Conversely, EU-OPS 1 is reasonable clear that for the prelanding check the certification factored distances should be used. The logic is that most of the certification factor is to accommodate the day to variability in landing, i.e. the pilot’s contribution. Thus, it would difficult for the pilot to justify (without an emergency) that his prelanding assessment was safe (EU-OPS 1.400), as any shorter distance would appear to be ‘less safe’ than the standard required for dispatch, and that the pilot was still a significant (unchanged) contributor to landing variability.

Re tailwinds: The Flight Test Guide for Certification for Transport Category Airplanes AC 25-7A states “The AFM should contain a statement that the limitation for tailwinds greater than 10 knots reflects the capability of the airplane as evaluated in terms of airworthiness but does not constitute approval for operation in tailwinds exceeding 10 knots.”
AFAIK, the 737 AFM has no such statement, thus this suggests that ‘operational approval’ has been given (local FAA?). In this processes there is opportunity for an ill-considered approval (e.g. use the same one as previous 737 variants), and perhaps without full consideration of the potential risks which perhaps the certification regulations suggest.