PPRuNe Forums - View Single Post - Why Boeing can not use assumed on contaminated Runway?
Old 19th Mar 2016, 17:32
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RAT 5
 
Join Date: Jun 2000
Location: last time I looked I was still here.
Posts: 4,509
Indeed Denti. It takes quite a bit of head scratching for cadets to begin to understand this idea: i.e. less mph = more weight. Back to reduced thrust and contaminated runways: this is another head scratcher. You can use derate 1 or 2 - full, but you can't use full power with assumed temp.
Previously, we had a discussion about the use of derate & assumed temp and I asked why we don't just use assumed temp from full power, as some XAA's insist. The answer was to do with climb thrust v 25% reduction etc. or some such. Thus derate & assumed could be better. BUT, somewhere (B737) 26k assumed temp = derate 1 or 2 full. So the XAA's that insist on 26k only, and then assumed temp, would insist on 26k on contaminated runways, where as another XAA would allow derate 1 or 2 full. They can't both be correct from a safety point of view. To me thrust v weight is a question of physics to satisfy the takeoff performance, both on the ground and in the takeoff segments. Thrust also effects VMCG & VMCA. Thrust is thrust no matter how it is calculated via 26K 24K or 22K.
I'm only a simple northerner where a spade is a bloody shovel.
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