Originally Posted by
bellcrank88
Also I recall from Perf A that the headwind is factored by 50% and the tailwind by 150%. So what does this really mean. (ie what if I have 10 knots vs 0 knots?)
It means that the headwind credit used for the calculation is 50% of the (beneficial) effect and the tailwind effect used is 150% of the (detrimental) effect.
So a reported 10kt headwind is calculated as if the real headwind were 5kts, and a reported 10kt tailwind calculated as if the real tailwind were 15kts.
If the reported headwind is 10kts, and the real value drops below 5kts (such as to 0), your calculations lose all margin of conservatism wrt wind and you eat into "other" margins, if any.
Also, because the margin used for wind is proportional to the wind, with a high reported wind you have a fair margin. At near-calm conditions the margin is negligible (50% of 0 being 0)