In order to determine whether data is acceptable for estimating model parameters, the items in Table 6.1 must be addressed.

• Is the signal to noise ratio large enough?                   
• Is the input signal nearly a perfect step?                    
• Are the assumptions of the model identification method which is to be used valid? (i.e. smooth, S-shaped output response)                                         
• Did process begin at steady state?                             
• Did the process achieve a new steady state?              

The data satisfy these criteria, but this is not enough!  We must be sure that the data represents the effect of the (one) manipulated variable on the measured variable, with no other important input variables changing significantly.  Is this true for our data?

We note that the fuel flow increased, but the measured temperature decreased!  This would lead us to question the data and perform another experiment, this time with a return step to check for disturbances.

As an exercise, list several possible causes for the decreasing temperature, even though the fuel increased.  You might want to refer back to the process sketch.