Composite Runway Slope
A question for others doing Performance Engineering in the area of Airport Analysis, production of RTOWs, and the writing of programmes for generating RTOWs.
The traditional application of a runway with composite slope has been to use the mean slope, as AFM data and computer programmes for generating RTOWs typically deal with one single value of slope. In the past, I too, have used mean slope, but with concern.
The runways that concern me most are the 'humping runways, i.e. an initial UP slope, traversing the hump, and followed by a DOWN slope. One runway that I deal with has a 0.5% UP slope for the first half, and a 0.7% DOWN slope for the second half. Using mean slope (0.2% DOWN), I consider to be unrealistic as Acceleration (over the UP slope) will be poorer than expected, and Deceleration over the DOWN slope during an Accelerate-Stop will also be poorer. Thus, the RTOW produced may exceed the actual maximum weight at which an Accelerate-Stop manoeuvre could be safely carried out. (I would consider a 'dipping' runway to be safer).
My solution was to rewrite the programme to do a triple computer run for the runway, one using the greatest UP slope, one using the MEAN slope, and a third using the greatest DOWN slope. The resultant published RTOW is the least of the 3 results. Yes, it is somewhat conservative, but I sleep better at night. The remaining problem is what to tell crews to do if an RTOW is invalidated, and they must resort to 'General Charts'. At present, my instruction is to use MEAN slope.
Very interested to hear other's approach to the problem.
Regards,
Old Smokey