Snowonice,
If your particular AFM doesn't give you the data you seek, try the relevant Boeing performance programme or approach Boeing Customer Support for more data.
I might be looking at a different 737 QRH here but, subject to that caveat, my conservative view is that one ought to treat unfactored data with extreme caution. I suggest that unfactored means, in effect, routinely unachievable and needs to be factored by the pilot in any case for comparative assessment of emergency strategies.
For instance, a reasonable approach for landing distance assessment is to assess the conditions (ie select the table) conservatively (keeping in mind that one's assessment is at best a guess) and then factor the resulting unfactored distance by 43 percent and 67 percent (call it 50 and 70 for ease of calculations) which gives data bearing some relation to the (in some jurisdictions valid) alternate and the normal destination landing distances.
If the pilot has an available distance in excess of the highest figure, then the operation is akin to a normal landing, if between the highest and the middle figures, then the landing ought to be treated with considerable caution and care and, if between the middle and unfactored figures, then the landing becomes an emergency situation with a heightened risk of runway excursion. If the available distance is less than the unfactored, then one ought to anticipate a guaranteed overrun.
Perhaps with luck we might get Mutt's observations on this as he has lots of good gen on contaminated runways ....
Do keep in mind that the certification data in the AFM are determined for artificially structured circumstances which may not be reflected in the real world case at the time the pilot has to make his decision ...
I suggest that the 15 percent factor only is appropriate for using normal dry data in wet (not flooded) conditions.
[ 10 January 2002: Message edited by: john_tullamarine ]</p>