Fokker 50 PEC fault
 

In the F50, when a Prop Electronic Control fails the Np will go to 104%

The QRH then states that a speed limit of 220 knots TAS (not IAS) applies.

Anyone know why this limit would be a TAS and not an IAS?

It's definately not a typo in the QRH as a table is provided for you to work out TAS limits at various levels based on IAS.

My ill informed guess Crash is that it is to do with issues of compressibility or mach no at the blade tips at high TAS and high RPM.

Spot on.

Thanks for that guys,

Now I have a direction to head in whilst looking for a definitive answer.

Cheers