Max airspeeds at high altitudes

[Buran]

Hello people,

When I'm flying my Boeing 737-800 at high altitudes, I noticed that my maximum airspeed decreeses. Is there a place where I can find
these speeds? I don't want to try it out, since FSPAssengers wil give me a penalty for flying to fast.

Thanks in advance,

Buran

[whiskey-zulu]

The KIAS decreases, but the Mach number and ground speed increase; at high altitudes you should fly according to Mach number opposed to KIAS.
According to FSX B738 kneeboard, the cruise speed at FL280 or higher is 0.78 Mach, though you can go up to Mach 0.83 before you hit overspeed.

[Buran]

I can't find that page on the kneeboard, should it be under "Aircraft reference"?

[whiskey-zulu]

I believe it should be under that page as one of the reference speeds I think.