CPCS Back Up Mode

[jetset]

Hi TBM Community,

today the first time I get a yellow Message which shows "CPCS Back Up Mode" during the approach. I didnt find anything about it. Could someone explain whats going on in this case?

Thx in advance

Mark

[Goran_M]

CPCS backup is a mode of the GASC (Global Air Supply Controller) when it loses certain critical sensor inputs (such as cabin pressure differential, or aircraft barometric altitude). Basically the controller then can't provide reasonable cabin altitude control, so it defaults to a "safe-in-all-conditions" cabin altitude of 9800 ft.
Below 9800 ft your automatic outflow valve negative differential protection will make sure the cabin altitude doesn't exceed flight altitude by too much (meaning, the pressure in the cabin would be lower than the outside air). But above 9,800 ft flight altitude, the cabin will essentially become locked to 9,800 cabin altitude and stay there for the entire flight.

For reference, this is in the POH in the ECS section.

Edited September 16, 2019 by Goran_M

[jetset]

Thx Goran for your explanation! Just wondering as I didnt have this message not before and in the meantime I made around 60 flights

[Goran_M]

you'll get more of these little surprised.  Just be prepared.  All part of the wear and tear.