Hi, on that STAR into EHAM there's a 280 kt constraint at FL240. I don't know exactly when the real 744 would change to 280, but PSX changes to 280 at the T/D already as the deceleration before FL240 will start very soon anyway. This makes the path prediction more robust. If the SEL SPD is set to 260 already under such conditions, PSX will set 260 instead of 280.
If you delete that 280 constraint before the DES starts, the FMC will switch to IAS when M.844 rises to 260 KIAS. However, this is already the case at CRZ ALT. When you descend with a fixed Mach, the IAS will rise. If you set a higher IAS, say, .844/290, the FMC will keep .844 until the IAS rises to 290 kt. In this scenario, the IAS at CRZ ALT is below 290 kt. So there's some headroom for the rising IAS during the descent.
The crossover is smooth. There's no speed bug jump. This is because the FMC sets the crossover altitude at the .844/290 crossover, not at the fixed crossover altitude which the MCP SPD uses. The FMC will not rise the IAS and then suddenly jump back to 260.
|-|ardy
