Usually transport aircraft are certified only for plus or minus 2% runway slope with special approval required for more. I seem to remember an Alaska L382 carrier having FAA approval for a much steeper runway slope at certain unique airports.
A lot depends on airport versus aircraft type. While not specifically about runways with a slope, we used to land turboprops on a fairly short snow covered runway and ignored the PAPIs close-in as the would have you land far down the runway. In fact on most of the shortish runways, we would "dip" the PAPIs when close-in. It was never a problem being less than 50 feet over the threshold in those types with a nose low attitude on approach.
No doubt some people will disagree on doing this.
Last edited by JammedStab; 7th May 2014 at 23:29.