Cruise speed question

[unairspace]

Hi there,

I have a cruise speed question for A350-900. I recently fly short legs for testing purpose and found that cuirse speed is a mystery for me. Yestday I did a LFPO-LFBO flight, CI=30, cuirse altitude=FL280. During the climb phase it went all normal, once the aircraft reach FL280 the magaged speed is reduced to 234 KIAS. This happens on every 'low cuirse level' flights. Can someone please tell me what did I do wrong?

 

[marius1411]

Hi I have the same problem, the Cost Index in the CRZ Phase seems to be broken and not have an effect on th Managed Speed.

[richboy2307]

Hi,

On 3/5/2025 at 7:32 AM, unairspace said:

This happens on every 'low cuirse level' flights. Can someone please tell me what did I do wrong?

No there's nothing you're doing wrong as far as I can tell. Thanks passed on the your reports to the team.

4 hours ago, marius1411 said:

the Cost Index in the CRZ Phase seems to be broken and not have an effect on th Managed Speed.

It does have an effect, but its nowhere near to the same extent as some of the other aircraft, especially at the upper levels (~FL310+). The optimum CRZ MACH range is very narrow, 0.85-0.86 at its narrowest between CI 0 and 999. The 787 is quite similar in that regard, so a narrow margins in CRZ MACH is expected behaviour. 

Thanks!