11.2 When determining the maximum weight for landing of a jet-engined aeroplane of maximum take-off weight greater than 5 700 kg for the purpose of subparagraph 5.1 (a), the landing distance required is 1.67 times the distance required to bring the aeroplane to a stop on a dry runway or, if actual landing distance data is supplied by the aircraft’s type certificate holder, 1.15 times the actual landing distance.
Civil Aviation Order 20.7.1B - Aeroplane weight & performance limitations - Aeroplanes above 5 700kg - All operations (turbine & piston-engined) (02/12/2004)
Originally Posted by buttscratcher
So one would assume 'Full Factor' to be Dispatch at 1.92%
You are assuming the the operator does not use actual landing distance data, and thus would require the 1.92 times
dry distance factoring for dispatch. I am basing my comments on assumption the operator would be using the actual
wet landing distance data and thus only requires a 1.15 factor.
The SAFO and my comments apply to the 1.15 actual landing distance case. My point is that on a smooth runway (not grooved and not PFC) the 1.15 factor for actual landing distance data has proved to be inadequate for even moderate rainfall intensity. Thus, for a smooth runway consider the possibility that the runway friction performance will be similar to a contaminated one, even in moderate rain according to the SAFO.
It is difficult to pin down the exact definition of moderate and heavy rain, moderate rainfall is in the range of 0.5mm (lower bound) to between 4.0 & 7.6mm (upper bound) per hour, dependant upon who is defining it. The Newman reported rainfall was 3.6mm of rain between 0700 and 0730, thus a rainfall intensity of around 7.2mm per hour, at the upper band of the least conservative moderate range. Combined with the previous 120mm in the previous 21+ hours there is a high probability that drainage from the runway would be poorer than a single intense shower, and thus braking action is likely to be significantly worse than the wet actual landing distance certification data assumes.
Of course if the operator is not using actual landing distance data, my arguments are invalidated.
There isn't any need to be rude, we are all here to learn and avoiding becoming the subject of an accident report ourselves. Crews are still being caught out on wet runways, caution is warranted and a good knowledge of the issues and limitations of the landing distance calculations is essential, particularly when the runway is short. There have been many previous near misses and accidents recently with wet runway excursions / near misses. Off the top of my head,
Jacksonville 738 accident (the crew ignored multiple heavy rainfall reports at the field), SWA at Burbank (twice) and the
Virgin Christchurch reduced braking effectiveness (excellent report covering reduced friction with just a small portion of the runway contaminated in light rain causing a very close call for the crew).
A close read of
SAFO 19003, pondering it's implications, and then considering the last 10 minute rainfall on the AWIS or TTF will help keep you out of the mud.