Oftentimes it is a real free-for-all as aircraft try to get the optimum flight levels. Leaving Japanese airspace eastbound across the Pacific all the evening's traffic bound for the US from various Asian nations seems to converge at a point off the east coast of Japan. The first aircraft to the chosen flight levels wins. What this means is that some aircraft climb too high too early to ensure they will evenually be at their optimum flight level. If you get stuck behind and below one of these types it can take hours before you can climb to your planned flight level. It can murder your fuel planning.
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