Yes, the TSIO-550 uses a slope controller. I’m not familiar with the VAPC. The slope controller is pretty simple in that it converts a MP signal to oil pressure.  The oil pressure regulates the wastesgate.  Do you think the MP pressure changes during climb and decent are coming from a fixed wastegate and changes in ram air pressure?  The groundspeed varied from 235 kts to 185 kts.  (I don’t record airspeed)  I thought of this but can’t get there from here.

 

I also agree, the pressure relief valve must not be working correctly and that needs to be fixed as well.

We have not pressurized the cabin.  The system is ready but the MP problem has consumed us.

 

On the fuel flow…..you are correct for a fixed MP, but as MP goes up, fuel rate goes up.  However, I’m not sure the curve I’m seeing is correct.  I get a 30% increase in fuel rate for a 10% increase in MP.

 

Too late on getting fixed quickly.  Pretty frustrating.  Every time I look at the flight data…..I grit my teeth.  

The new slope controller should be delivered today.  Craig Berland

 

If that were to have happened on my TSIO-520 engines I would immediately think the VAPC (variable absolute pressure controller) was operating with a fully closed wastegate and not regulating on takeoff.  I think you have the slope controller so I don't know if it is exactly the same situation but I think the WOT operation is identical.   In the pattern, it sounds like it is bootstrapping and simply fixed wastegate with changes in MP coming from airspeed changes.   The symptom that is interesting is the takeoff problem.  If the cabin is pressurized after takeoff and the bleed comes from turbocharger then that would suggest to me that the VAPC thinks it has less MP after takeoff then on the ground.  It sounds as if it is permitting a complete close of the wastegate and maximum MP.  That would translate into high fuel flows except (my recollection from the TSIO-520) that the maximum fuel flow should be limited to a maximum value in the fuel controller.  Also, if you have a maximum pressure relief valve that would pop at roughly 2 inches over maximum MP.   From your description, all the safety protection seems to have been bypassed.  Does that sound right?  Hope it gets resolved quickly.