Originally Posted by
Nicolaus
If I'm not mistaken, thrust reverse is not factored into landing distance for airline ops?
Kind of a weird/gray area. And what you said is usually the commonly held belief. I'd venture to guess it's based on airlines not using it and going with worst case. IOW, even under normal circumstances, you don't know they're actually going to work until all the airplane's logic is satisfied.
However, airlines can get "thrust reverser credit" for operative reverse when calculating certain distances under certain conditions;
Any credit for reverse is covered by the certification requirements - CS 25 or FAR 25.125
Means other than wheel brakes may be used if …
(i) Is safe and reliable;
(ii) Is used so that consistent results can be expected in service; and
(iii) Is such that exceptional skill is not required to control the aeroplane.
However, where reverse is included in contaminated data CS (AMC) 25.1591 7.4.3. (not in FAR) “
Performance information may include credit for reverse thrust where available and controllable”, the exposure to the higher risk is assumed to be balanced by operational caution, and by minimizing the number of landings, e.g. CS AMC 25.1591 8.1
“8.1.1 Operation on runways contaminated with water, slush, snow, ice or other contaminants implies uncertainties with regard to runway friction and contaminant drag and therefore to the achievable performance and control of the aeroplane during take-off, since the actual conditions may not completely match the assumptions on which the performance information is based. Where possible, every effort should be made to ensure that the runway surface is cleared of any significant contamination.”
And IIRC, the SW in MDW changed this up somewhat on either/both how much "credit" can be applied, or how little the "credit' can be, etc.