Some questions/observations about the landing performance referred to in the report.
I assume that this version of the 737 does not have any credit for thrust reverse in the certificated data, but it might do for estimated slippery/contaminated data or in the manufacturer’s actual distances.
There are minor differences in the operator’s presentation of the certificated data. Bulletin -07 refers to the total landing distance based on FAR +67/92%, but the landing card using the same basis, infers that the air distance is 1000ft, although the actual certification value might be a lot less. Thus the 1000ft quoted could hide the fact that even a 1000ft touchdown point eats-into the total factored distance.
The landing card also presents both the certificated factorised FAR data (WET/GOOD) and the estimated wet/contaminated data on the same page. Although the basis of each data set may be explained, the proximity of information might not provide sufficient emphasis to identify the significant difference in the risk to be considered when using the estimated wet/contaminated data vice wet/good.
How do other operators publish this data?
Bulletin –07 ‘runway condition table’ (Page 203) does not refer to water in the Medium (Fair) category, implying that this is associated with either fully factored wet performance (1.92) or standing water (>1/8in, 3mm) for the estimated contaminated performance. This omission might create a gap in stopping performance between those runway conditions covered by the 1.92 factored data and those using estimated - contaminated data; would 1.92 be sufficient for <1/8 Wet/Good, but not enough for Medium (fair) wet.
This method of presentation and the lack of descriptors might hinder crews’ consideration of wet conditions below the wet/good definition, because there is a weak (no) correlation between the reported conditions – rainfall rate, and the braking performance.
How do other operators publish this data?
On this latter point the FAA’s TALPA proposals use the same format; however they do acknowledge differences between wet grooved, smooth, and PFC runways but do not differentiate between them except for ‘slippery when wet’.
Other significant influences on performance are the runway texture (and condition) and depth of the tyre treads, but there are few references alerting pilots to these aspects.